Dr Rajiv Desai

An Educational Blog

HUMAN EVOLUTION

HUMAN EVOLUTION:

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Figure below shows conservator Effie Verveniotou and human origins researcher Dr Louise Humphrey examine the oldest nearly complete modern human skeleton ever found in Britain before it goes on display in the gallery. Cheddar Man is a human male fossil found in Gough’s Cave in Cheddar Gorge, Somerset, England. Excavated in 1903, Cheddar Man is Britain’s oldest complete human skeleton. Cheddar Man lived around 10,000 years ago. Analysis of his nuclear DNA indicates that he was a typical member of the western European population at the time, with lactose intolerance, dark skin, blue eyes, and dark curly or wavy hair.

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Prologue:

Recently, minister of state for human resource development of India said that the Darwinian theory of evolution was scientifically wrong and should not be taught in Indian institutions. Many scientists and students signed a petition calling upon him to withdraw his remarks. Three science academies of India issued a joint statement, pointing out that those remarks had no scientific basis, and that it would be retrogressive to stop the teaching of evolution. Evolution has become bone of contention between science and religion. Creationism is a religious belief that the universe and life originated “from specific acts of divine creation”, as opposed to the scientific conclusion that they came about through natural processes. Every extinct and extant species on earth have resulted from the same evolutionary processes determining the way they are through shaping their morphology, physiology, and behavior. The traits specific for the human species are the result of the same evolutionary processes responsible for any other living creature. From a general evolutionary perspective, humans are consequently no different than any other species on the planet. Previously, the date, nature, and identity of the last common ancestor between modern humans and their closest living relatives were determined on the basis of comparative anatomy of living species and fragmentary fossil remains. Today, molecular genetic data play an increasing role in establishing phylogenetic relatedness between hominoids, the superfamily including all living and extinct ape and human species. Yet even in scientific disciplines, there is a widespread feeling that evolution is a minor issue in biology, irrelevant to modern advances in molecular biology and devoid of application potential. This could not be farther from the reality. Evolutionary biology is not a branch of biology the way immunology or biochemistry are. Rather, it is a unifying conceptual framework within which facts from all of biology get coherently arranged. Biology without evolution would be like chemistry without the knowledge of the periodic table and reaction mechanisms: an arbitrary collection of facts.

‘For a biologist, the alternative to thinking in evolutionary terms is not to think at all’.

— Peter B. Medawar, Nobel Laureate

An evolutionary perspective sheds light on issues of great societal relevance like why and how we age, how epidemics spread and new pathogenic strains arise, how to improve crops and domesticated animals, how to tackle the evolution of multi-drug resistance in bacteria, why nepotism and despotism are so common in human societies, how notions of justice have developed, why the sudden explosion of the so-called “lifestyle diseases”, to cite just a few examples. Understanding evolution helps us solve biological problems.

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Abbreviations and synonyms:

Mya = million year ago = Ma = my

Kya = thousand year ago = Ka = ky

LCA = last common ancestor

LUCA = last universal common ancestor

BP = Before Present = before 1 January 1950

TMRCA = time to the most recent common ancestor

CNS = conserved noncoding sequence

SNP = single nucleotide polymorphism

INDEL = insertion/deletion polymorphism

mtDNA = Mitochondrial DNA

EQ = encephalisation quotient

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Introduction to evolution:

In the simplest sense, evolution means the slow process of change from a simple to a more complex structure. Evolution assumes that all living things are inter-related. Humans are supposed to have developed from some simpler forms. Most of the scientists today accept the basic principle of evolution but they have varying views regarding how evolution has taken place or how far it has gone. The evolution of life began in the oceans. About four hundred million years ago the first land based creatures emerged. Some of these gradually evolved into the large reptiles who were later displaced by mammals. Mammals are warm-blooded creatures having greater capacity to learn from experience than other animals and this capacity has reached its highest development in the human species.

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Contrary to popular opinion, neither the term nor the idea of biological evolution began with Charles Darwin and his foremost work, On the Origin of Species by Means of Natural Selection (1859). Many scholars from the ancient Greek philosophers on had inferred that similar species were descended from a common ancestor. The word “evolution” first appeared in the English language in 1647 in a nonbiological connection, and it became widely used in English for all sorts of progressions from simpler beginnings. The term Darwin most often used to refer to biological evolution was “descent with modification,” which remains a good brief definition of the process today. Evolution, theory in biology postulating that the various types of plants, animals, and other living things on Earth have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations. The theory of evolution is one of the fundamental keystones of modern biological theory.

The diversity of the living world is staggering. More than 2 million existing species of organisms have been named and described; many more remain to be discovered—from 10 million to 30 million, according to some estimates. What is impressive is not just the numbers but also the incredible heterogeneity in size, shape, and way of life—from lowly bacteria, measuring less than a thousandth of a millimetre in diameter, to stately sequoias, rising 100 metres (300 feet) above the ground and weighing several thousand tons; from bacteria living in hot springs at temperatures near the boiling point of water to fungi and algae thriving on the ice masses of Antarctica and in saline pools at −23 °C (−9 °F); and from giant tube worms discovered living near hydrothermal vents on the dark ocean floor to spiders and larkspur plants existing on the slopes of Mount Everest more than 6,000 metres (19,700 feet) above sea level.

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The virtually infinite variations on life are the fruit of the evolutionary process. All living creatures are related by descent from common ancestors. Humans and other mammals descend from shrewlike creatures that lived more than 150 million years ago; mammals, birds, reptiles, amphibians, and fishes share as ancestors aquatic worms that lived 600 million years ago; and all plants and animals derive from bacteria-like microorganisms that originated more than 3 billion years ago. Biological evolution is a process of descent with modification. Lineages of organisms change through generations; diversity arises because the lineages that descend from common ancestors diverge through time.

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Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules. Repeated formation of new species (speciation), change within species (anagenesis), and loss of species (extinction) throughout the evolutionary history of life on Earth are demonstrated by shared sets of morphological and biochemical traits, including shared DNA sequences. These shared traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct a biological “tree of life” based on evolutionary relationships (phylogenetics), using both existing species and fossils. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilised multicellular organisms. Existing patterns of biodiversity have been shaped both by speciation and by extinction.

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The 19th-century English naturalist Charles Darwin argued that organisms come about by evolution, and he provided a scientific explanation, essentially correct but incomplete, of how evolution occurs and why it is that organisms have features—such as wings, eyes, and kidneys—clearly structured to serve specific functions. Natural selection was the fundamental concept in his explanation. Darwin proposed that evolution could be explained by the differential survival of organisms following their naturally occurring variation—a process he termed “natural selection.” According to this view, the offspring of organisms differ from one another and from their parents in ways that are heritable—that is, they can pass on the differences genetically to their own offspring. Furthermore, organisms in nature typically produce more offspring than can survive and reproduce given the constraints of food, space, and other environmental resources. If a particular off-spring has traits that give it an advantage in a particular environment, that organism will be more likely to survive and pass on those traits. As differences accumulate over generations, populations of organisms diverge from their ancestors. Natural selection occurs because individuals having more-useful traits, such as more-acute vision or swifter legs, survive better and produce more progeny than individuals with less-favourable traits. Thus, in successive generations members of a population are replaced by progeny of parents better adapted to survive and reproduce in the biophysical environment in which natural selection takes place. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are seemingly fitted for the functional roles they perform. The processes by which the changes occur, from one generation to another, are called evolutionary processes or mechanisms. The four most widely recognised evolutionary processes are natural selection (including sexual selection), genetic drift, mutation and gene migration due to genetic admixture. In the early 20th century the modern evolutionary synthesis integrated classical genetics with Darwin’s theory of evolution by natural selection through the discipline of population genetics. Genetics, a science born in the 20th century, reveals in detail how natural selection works and led to the development of the modern theory of evolution. The importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis, evolutionism, and other beliefs about innate “progress” within the largest-scale trends in evolution, became obsolete.  Beginning in the 1960s, a related scientific discipline, molecular biology, enormously advanced knowledge of biological evolution and made it possible to investigate detailed problems that had seemed completely out of reach only a short time previously—for example, how similar the genes of humans and chimpanzees might be (they differ in about 4 percent of the units that make up the genes).

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Darwin’s original hypothesis has undergone extensive modification and expansion, but the central concepts stand firm. Studies in genetics and molecular biology—fields unknown in Darwin’s time—have explained the occurrence of the hereditary variations that are essential to natural selection. Genetic variations result from changes, or mutations, in the nucleotide sequence of DNA, the molecule that genes are made from. Such changes in DNA now can be detected and described with great precision. Genetic mutations arise by chance. They may or may not equip the organism with better means for surviving in its environment. But if a gene variant improves adaptation to the environment (for example, by allowing an organism to make better use of an available nutrient, or to escape predators more effectively—such as through stronger legs or disguising coloration), the organisms carrying that gene are more likely to survive and reproduce than those without it. Over time, their descendants will tend to increase, changing the average characteristics of the population. Although the genetic variation on which natural selection works is based on random or chance elements, natural selection itself produces “adaptive” change—the very opposite of chance.

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Chance and randomness do factor into evolution and the history of life in many different ways; however, some important mechanisms of evolution are non-random. For example, consider the process of natural selection, which results in adaptations — features of organisms that appear to suit the environment in which the organisms live (e.g., the fit between a flower and its pollinator, the coordinated response of the immune system to pathogens, and the ability of bats to echolocate). Such amazing adaptations clearly did not come about “by chance.” They evolved via a combination of random and non-random processes. The process of mutation, which generates genetic variation, is random, but selection is non-random. Selection favored variants that were better able to survive and reproduce (e.g., to be pollinated, to fend off pathogens, or to navigate in the dark). Over many generations of random mutation and non-random selection, complex adaptations evolved.  However, natural selection has no foresight and no intentions. Natural selection cannot select a trait that is unavailable in genetic variation.  If a population or species doesn’t happen to have the right kinds of genetic variation, it will not evolve in response to the environmental changes and may become extinct. So although selection is not random, genetic variation is random, therefore chance or randomness is very significant factor in evolution of life.

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Scientists also have gained an understanding of the processes by which new species originate. A new species is one in which the individuals cannot mate and produce viable descendants with individuals of a preexisting species. The split of one species into two often starts because a group of individuals becomes geographically separated from the rest. This is particularly apparent in distant remote islands, such as the Galápagos and the Hawaiian archipelago, whose great distance from the Americas and Asia means that arriving colonizers will have little or no opportunity to mate with individuals remaining on those continents. Mountains, rivers, lakes, and other natural barriers also account for geographic separation between populations that once belonged to the same species. Once isolated, geographically separated groups of individuals become genetically differentiated as a consequence of mutation and other processes, including natural selection. The origin of a species is often a gradual process, so that at first the reproductive isolation between separated groups of organisms is only partial, but it eventually becomes complete. Scientists pay special attention to these intermediate situations, because they help to reconstruct the details of the process and to identify particular genes or sets of genes that account for the reproductive isolation between species. A particularly compelling example of speciation involves the 13 species of finches studied by Darwin on the Galápagos Islands, now known as Darwin’s finches. The ancestors of these finches appear to have immigrated from the South American mainland to the Galápagos. Today the different species of finches on the island have distinct habitats, diets, and behaviors, but the mechanisms involved in speciation continue to operate. A research group led by Peter and Rosemary Grant of Princeton University has shown that a single year of drought on the islands can drive evolutionary changes in the finches. Drought diminishes supplies of easily cracked nuts but permits the survival of plants that produce larger, tougher nuts. Droughts thus favor birds with strong, wide beaks that can break these tougher seeds, producing populations of birds with these traits. The Grants have estimated that if droughts occur about once every 10 years on the islands, a new species of finch might arise in only about 200 years.

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Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates – in particular genus Homo – and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes. This process involved the gradual development of traits such as human bipedalism and language. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, neurobiology, ethology, linguistics, evolutionary psychology, embryology and genetics. Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, and the earliest fossils appear in the Paleocene, around 55 million years ago. Within the Hominoidea (apes) superfamily, the Hominidae family diverged from the Hylobatidae (gibbon) family some 15–20 million years ago; African great apes (subfamily Homininae) diverged from orangutans (Ponginae) about 14 million years ago; the Hominini tribe (humans, Australopithecines and other extinct biped genera, and chimpanzee) parted from the Gorillini tribe (gorillas) between 9 million years ago and 8 million years ago; and, in turn, the subtribes Hominina (humans and biped ancestors) and Panina (chimps) separated about 7.5 million years ago to 5.6 million years ago.

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A common misconception is that evolution has goals, long-term plans, or an innate tendency for “progress”, as expressed in beliefs such as orthogenesis and evolutionism; realistically however, evolution has no long-term goal and does not necessarily produce greater complexity. Although complex species have evolved, they occur as a side effect of the overall number of organisms increasing and simple forms of life still remain more common in the biosphere. For example, the overwhelming majority of species are microscopic prokaryotes, which form about half the world’s biomass despite their small size, and constitute the vast majority of Earth’s biodiversity. Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it is more noticeable. Indeed, the evolution of microorganisms is particularly important to modern evolutionary research, since their rapid reproduction allows the study of experimental evolution and the observation of evolution and adaptation in real time.

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In terms of practical application, an understanding of evolution has been instrumental to developments in numerous scientific and industrial fields, including agriculture, human and veterinary medicine, and the life sciences in general. Discoveries in evolutionary biology have made a significant impact not just in the traditional branches of biology but also in other academic disciplines, including biological anthropology, and evolutionary psychology. Evolutionary computation, a sub-field of artificial intelligence, involves the application of Darwinian principles to problems in computer science.

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Evolutionary history of life:

The evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved since life appeared on the planet, until the present.

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Origin of life:

The Earth is about 4.54 billion years old. Highly energetic chemistry is thought to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed. The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions. The beginning of life may have included self-replicating molecules such as RNA and the assembly of simple cells.  All life on Earth shares a common ancestor known as the last universal common ancestor (LUCA), which lived approximately 3.5–3.8 billion years ago. A December 2017 report stated that 3.45 billion year old Australian rocks once contained microorganisms, the earliest direct evidence of life on Earth. Nonetheless, this should not be assumed to be the first living organism on Earth; a study in 2015 found “remains of biotic life” from 4.1 billion years ago in ancient rocks in Western Australia. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all organisms living on Earth. More than 99 percent of all species, amounting to over five billion species that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth’s current species range from 10 million to 14 million, of which about 1.9 million are estimated to have been named and 1.6 million documented in a central database to date, leaving at least 80 percent not yet described. In May 2016, one study reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. Another 2011 study predicts ∼8.7 million species globally, of which ∼2.2 million are marine. So even today we do not know total number of species on earth accurately.

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Evolution of life:

Prokaryotes inhabited the Earth from approximately 3–4 billion years ago. No obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years. The eukaryotic cells emerged between 1.6–2.7 billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiosis. The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or hydrogenosomes. Another engulfment of cyanobacterial-like organisms led to the formation of chloroplasts in algae and plants. The history of life was that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacaran period. The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime moulds and myxobacteria. In January 2016, scientists reported that, about 800 million years ago, a minor genetic change in a single molecule called GK-PID may have allowed organisms to go from a single cell organism to one of many cells. Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the Cambrian explosion. Here, the majority of types of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis. About 500 million years ago, plants and fungi colonised the land and were soon followed by arthropods and other animals. Insects were particularly successful and even today make up the majority of animal species. Amphibians first appeared around 364 million years ago, followed by early amniotes and birds around 155 million years ago (both from “reptile”-like lineages), mammals around 129 million years ago, homininae around 10 million years ago and modern humans around 250,000 years ago. However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.

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Evolution of plants:

The evolution of plants has resulted in widely varying levels of complexity, from the earliest algal mats, through bryophytes, lycopods, and ferns, to the complex gymnosperms and angiosperms of today. While many of the groups which appeared earlier continue to thrive, as exemplified by algal dominance in marine environments, more recently derived groups have also displaced previously ecologically dominant ones, e.g. the ascendance of flowering plants over gymnosperms in terrestrial environments. Evidence for the appearance of the first land plants occurs in the Ordovician, around 450 million years ago, in the form of fossil spores.  Land plants began to diversify in the Late Silurian, from around 430 million years ago, and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert, formed in volcanic hot springs, preserved several species of early plants in cellular detail by petrification. By the middle of the Devonian, many of the features recognised in plants today were present, including roots and leaves. Late Devonian free-sporing plants such as Archaeopteris had secondary vascular tissue that produced wood and had formed forests of tall trees. Also by late Devonian, Elkinsia, an early seed fern, had evolved seeds. Evolutionary innovation continued into the Carboniferous and is still ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the appearance of the flowering plants in the Triassic (~200 million years ago), and their later diversification in the Cretaceous and Paleogene. The latest major group of plants to evolve were the grasses, which became important in the mid-Paleogene, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO2 and warm, dry conditions of the tropics over the last 10 million years.

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Life timeline:

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Common descent:

All organisms on Earth are descended from a common ancestor or ancestral gene pool. Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events. The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits and finally, that organisms can be classified using these similarities into a hierarchy of nested groups—similar to a family tree. However, modern research has suggested that, due to horizontal gene transfer, this “tree of life” may be more complicated than a simple branching tree since some genes have spread independently between distantly related species. Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry. More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids. The development of molecular genetics has revealed the record of evolution left in organisms’ genomes: dating when species diverged through the molecular clock produced by mutations. For example, these DNA sequence comparisons have revealed that humans and chimpanzees share 96% of their genomes and analysing the few areas where they differ helps shed light on when the common ancestor of these species existed.

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Humans are a young species, in geological terms. The average “lifespan” of a mammal species, measured by its duration in the fossil record, is around 10 million years. While hominids have followed a separate evolutionary path since their divergence from the ape lineage, around 7 million years ago, our own species (Homo sapiens) is much younger. Fossils classified as archaic H. sapiens appear about 400,000 years ago, and the earliest known modern humans date back only 170,000 years. Human evolution is about the origin of human beings. All humans belong to the same species, which has spread from its birthplace in Africa to almost all parts of the world. Its origin in Africa is proved by the fossils which have been found there. The term ‘human’ in this context means the genus Homo. However, studies of human evolution usually include other hominids, such as the Australopithecines, from which the genus Homo had diverged (split) by about 2.3 to 2.4 million years ago in Africa. The first Homo sapiens, the ancestors of today’s humans, evolved around 200,000 years ago. The biological name for “human” or “man” is Homo. The modern human species is called Homo sapiens. “Sapiens” means “thought”. Homo sapiens means “the thinking man”.  Our knowledge of human evolution is changing rapidly, as new fossils are discovered and described every year. Thirty years ago, it was generally accepted that humans and the great apes last shared a common ancestor perhaps 16-20 million years ago, and that the separate human branch was occupied by only a few species, each evolving from the one before. Now we know, through a combination of new fossil finds and molecular biology, that humans and chimpanzees diverged as little as 7 million years ago, and that our own lineage is “bushy”, with many different species in existence at the same time. Our view of our evolutionary past has changed as social attitudes have changed. Darwin was remarkably prescient when he wrote, in 1871 “The Descent of Man”, that humans had evolved in Africa and were closely related to the great apes (gorilla, chimpanzee, and orang-utan). But at that time this view was anathema to many, since the majority of people still accepted the concept of special creation. This is why the first fossil hominid material to be discovered, that of Neanderthal Man, attracted even more controversy than the later discoveries of Australopithecus africanus and Homo erectus. Rather than accept the fossil as the remains of a human ancestor, the distinguished German scientist R. Virchow described it as the skeleton of a diseased Cossack cavalryman. And even once the antiquity of the remains was established, many scientists refused to accept that Neanderthals could be closely related to modern humans, depicting them instead as brutish and apelike. This interpretation reflected the prevailing prejudices about human ancestry, and was supported by misinterpretation of the remains of the “Old Man of La Chapelle”, whose skeleton was warped by arthritis.

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Macroevolution and microevolution:

The outcomes of evolution are distinguished based on time scale as macroevolution versus microevolution. Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction; whereas microevolution refers to smaller evolutionary changes within a species or population, in particular shifts in gene frequency and adaptation. In general, macroevolution is regarded as the outcome of long periods of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one—the difference is simply the time involved. Microevolutionary processes occurring over thousands or millions of years can add up to large-scale changes that define new species or groups. However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows a species to rapidly adapt to new habitats, lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution might involve selection at different levels—with microevolution acting on genes and organisms, versus macroevolutionary processes such as species selection acting on entire species and affecting their rates of speciation and extinction.

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Convergent and divergent evolution:

Convergent evolution occurs in different species that have evolved similar traits independently of each other due to natural selection. Convergent evolution describes the independent evolution of similar features in species of different lineages. Examples of convergent evolution include the relationship between bat and insect wings, shark and dolphin bodies, and vertebrate and cephalopod eyes. One of the most well-known examples of convergent evolution is the camera eye of cephalopods (e.g., octopus), vertebrates (e.g., mammals), and cnidaria (e.g., box jellies). Their last common ancestor had at most a very simple photoreceptive spot, but a range of processes led to the progressive refinement of this structure to the advanced camera eye. There is, however, one subtle difference: the cephalopod eye is “wired” in the opposite direction, with blood and nerve vessels entering from the back of the retina, rather than the front as in vertebrates. Convergent evolution is similar to, but distinguishable from, the phenomenon of parallel evolution. Parallel evolution occurs when two independent but similar species evolve in the same direction and thus independently acquire similar characteristics; for example, gliding frogs have evolved in parallel from multiple types of tree frog. Traits arising through convergent evolution are analogous structures, in contrast to homologous structures, which have a common origin, but not necessarily similar function. The British anatomist Richard Owen was the first scientist to recognize the fundamental difference between analogies and homologies. Bat and pterosaur wings are an example of analogous structures, while the bat wing is homologous to human and other mammal forearms, sharing an ancestral state despite serving different functions. The opposite of convergent evolution is divergent evolution, whereby related species evolve different traits. On a molecular level, this can happen due to random mutation unrelated to adaptive changes. Divergent evolution is the process by which a species with similar traits become groups that are tremendously different from each other over many generations.

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Vestigial Structures:

Vestigial structures have no function but may still be inherited to maintain fitness. Vestigial structure is a genetically determined structures or attributes that have lost most or all of their ancestral function in a given species. Examples of vestigial structures include the human appendix, the pelvic bone of a snake, and the wings of flightless birds. Vestigial structures can become detrimental, but in most cases these structures are harmless; however, these structures, like any other structure, require extra energy and are at risk for disease.  Vestigial structures are often homologous to structures that function normally in other species. The vestigial versions of a structure can be compared to the original version of the structure in other species in order to determine the homology of the structure. Homologous structures indicate common ancestry with those organisms that have a functional version of the structure. Therefore, vestigial structures can be considered evidence for evolution, the process by which beneficial heritable traits arise in populations over an extended period of time. Vestigial traits can still be considered adaptations because an adaptation is often defined as a trait that has been favored by natural selection. Adaptation is modification of something or its parts that make it more fit for existence under the conditions of its current environment.  Adaptations, therefore, need not be adaptive, as long as they were at some point. The existence of vestigial traits can be attributed to changes in the environment and behavior patterns of the organism in question. As the function of the trait is no longer beneficial for survival, the likelihood that future offspring will inherit the “normal” form of it decreases. In some cases the structure becomes detrimental to the organism. Vestigial structures, especially non-harmful ones, take a long time to be phased out since eliminating them would require major alterations that could result in negative side effects.

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Now I will discuss various processes related to evolution:

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  1. Heredity:

Evolution in organisms occurs through changes in heritable traits—the inherited characteristics of an organism. In humans, for example, eye colour is an inherited characteristic and an individual might inherit the “brown-eye trait” from one of their parents. Inherited traits are controlled by genes and the complete set of genes within an organism’s genome (genetic material) is called its genotype. The complete set of observable traits that make up the structure and behaviour of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment. As a result, many aspects of an organism’s phenotype are not inherited. For example, suntanned skin comes from the interaction between a person’s genotype and sunlight; thus, suntans are not passed on to people’s children. However, some people tan more easily than others, due to differences in genotypic variation; a striking example are people with the inherited trait of albinism, who do not tan at all and are very sensitive to sunburn. Heritable traits are passed from one generation to the next via DNA, a molecule that encodes genetic information. DNA is a long biopolymer composed of four types of bases. The sequences of bases along a particular DNA molecule specify the genetic information, in a manner similar to a sequence of letters spelling out a sentence. Before a cell divides, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. Portions of a DNA molecule that specify a single functional unit are called genes; different genes have different sequences of bases. Within cells, the long strands of DNA form condensed structures called chromosomes. The specific location of a DNA sequence within a chromosome is known as a locus. If the DNA sequence at a locus varies between individuals, the different forms of this sequence are called alleles. DNA sequences can change through mutations, producing new alleles. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism. However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by quantitative trait loci (multiple interacting genes). Recent findings have confirmed important examples of heritable changes that cannot be explained by changes to the sequence of nucleotides in the DNA. These phenomena are classed as epigenetic inheritance systems. DNA methylation marking chromatin, self-sustaining metabolic loops, gene silencing by RNA interference and the three-dimensional conformation of proteins (such as prions) are areas where epigenetic inheritance systems have been discovered at the organismic level. Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlay some of the mechanics in developmental plasticity and canalisation. Heritability may also occur at even larger scales. For example, ecological inheritance through the process of niche construction is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effects that modify and feed back into the selection regime of subsequent generations. Descendants inherit genes plus environmental characteristics generated by the ecological actions of ancestors.  Other examples of heritability in evolution that are not under the direct control of genes include the inheritance of cultural traits and symbiogenesis.

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  1. Variation:

Individuals of a species have similar characteristics but they are rarely identical, the difference between them is called variation. Genetic variation is a result of subtle differences in our DNA. An individual organism’s phenotype results from both its genotype and the influence from the environment it has lived in. A substantial part of the phenotypic variation in a population is caused by genotypic variation. The modern evolutionary synthesis defines evolution as the change over time in this genetic variation. The frequency of one particular allele will become more or less prevalent relative to other forms of that gene. Variation disappears when a new allele reaches the point of fixation—when it either disappears from the population or replaces the ancestral allele entirely.  Natural selection will only cause evolution if there is enough genetic variation in a population. The Hardy–Weinberg principle provides the solution to how variation is maintained in a population with Mendelian inheritance. The frequencies of alleles (variations in a gene) will remain constant in the absence of selection, mutation, migration and genetic drift. Variation comes from mutations in the genome, reshuffling of genes through sexual reproduction and migration between populations (gene flow). Despite the constant introduction of new variation through mutation and gene flow, most of the genome of a species is identical in all individuals of that species. However, even relatively small differences in genotype can lead to dramatic differences in phenotype: for example, chimpanzees and humans differ in only about 5% of their genomes.

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Genome variations in humans:

Genome variations are differences in the sequence of DNA from one person to the next. The more closely related two people are, the more similar their genomes. Scientists estimate that the genomes of non-related people—any two people plucked at random off the street—differ at about 1 in every 1,200 to 1,500 DNA bases, or “letters.”  The haploid human genome contains approximately 3 billion base pairs of DNA packaged into 23 chromosomes. Of course, most cells in the body (except for female ova and male sperm) are diploid, with 23 pairs of chromosomes. That makes a total of 6 billion base pairs of DNA per cell.  Each chromosome contains hundreds to thousands of genes, which carry the instructions for making proteins. Each of the estimated 30,000 genes in the human genome makes an average of three proteins. But we are all 99.9 percent the same, DNA-wise. (By contrast, we are only about 96 percent the same as our closest relatives, chimpanzees.). Variations are found all throughout the genome, on every one of the 46 human chromosomes. The majority of variations are found outside of genes, in the “extra” or “junk” DNA that does not affect a person’s characteristics. Mutations in these parts of the genome are never harmful, so variations can accumulate without causing any problems. Genes, by contrast, tend to be stable because mutations that occur in genes are often harmful to an individual, and thus less likely to be passed on. Genome variations include mutations and polymorphisms. Technically, a polymorphism is a DNA variation in which each possible sequence is present in at least 1 percent of people. For example, a place in the genome where 93 percent of people have a T and the remaining 7 percent have an A is a polymorphism. If one of the possible sequences is present in less than 1 percent of people (99.9 percent of people have a G and 0.1 percent have a C), then the variation is called a mutation. Informally, the term mutation is often used to refer to a harmful genome variation that is associated with a specific human disease, while the word polymorphism implies a variation that is neither harmful nor beneficial. However, scientists are now learning that many polymorphisms actually do affect a person’s characteristics, though in more complex and sometimes unexpected ways. About 90 percent of human genome variation comes in the form of single nucleotide polymorphisms, or SNPs (pronounced “snips”). As their name implies, these are variations that involve just one nucleotide, or base. Any one of the four DNA bases may be substituted for any other—an A instead of a T, a T instead of a C, a G instead of an A, and so on. Theoretically, a SNP could have four possible forms, or alleles, since there are four types of bases in DNA. But in reality, most SNPs have only two alleles. For example, if some people have a T at a certain place in their genome while everyone else has a G, that place in the genome is a SNP with a T allele and a G allele. The human genome contains more than 2 million SNPs.

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Genetic diversity vs. genetic variation:

Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary. Genetic variation is simply the variation in alleles of genes in the gene pool of a species or a population. Genetic variation lays the foundation for organisms to have genetic diversity, which contributes eventually for biodiversity through species diversity. Variety and variability collectively contribute for the diversity; hence, the existence of variations and diversity in genetic materials definitely helps the species to thrive through increased adaptability for the changing environmental conditions.

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Gene (allele) frequency:

Allele frequency, or gene frequency, is the relative frequency of an allele (variant of a gene) at a particular locus in a population, expressed as a fraction or percentage.  Specifically, it is the fraction of all chromosomes in the population that carry that allele. Microevolution is the change in allele frequencies that occurs over time within a population. Allele frequency is an accurate measurement of the amount of genetic variation in a population. In population genetics, allele frequencies are used to describe the amount of variation at a particular locus or across multiple loci. The gene pool is the sum total of all the genes and combinations of genes that occur in a population of organisms of the same species. It can be described by citing the frequencies of the alternative genetic constitutions. Consider, for example, a particular gene (which geneticists call a locus), such as the one determining the MN blood groups in humans. One form of the gene codes for the M blood group, while the other form codes for the N blood group; different forms of the same gene are called alleles. The MN gene pool of a particular population is specified by giving the frequencies of the alleles M and N. Thus, in the United States the M allele occurs in people of European descent with a frequency of 0.539 and the N allele with a frequency of 0.461—that is, 53.9 percent of the alleles in the population are M and 46.1 percent are N. In other populations these frequencies are different; for instance, the frequency of the M allele is 0.917 in Navajo Indians and 0.178 in Australian Aboriginals.

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  1. Mutation:

Every human genome is different because of mutations—”mistakes” that occur occasionally in a DNA sequence. When a cell divides in two, it makes a copy of its genome, then parcels out one copy to each of the two new cells. Theoretically, the entire genome sequence is copied exactly, but in practice a wrong base is incorporated into the DNA sequence every once in a while, or a base or two might be left out or added. These mistakes—”changes” might be a more accurate word, because they are not always bad news—are called mutations. When a mutation occurs in a sex cell—a sperm or an egg—it can be passed along to the next generation of people. Your genome contains about 60 “new” mutations—changes that occurred as your parents’ bodies made the egg and sperm cells that became you. These genome variations are uniquely yours. Other variations in your genome arose many generations ago and have been passed down from parent to child over the years, until they ended up in you.  Mutations are changes in the DNA sequence of a cell’s genome. When mutations occur, they may alter the product of a gene, or prevent the gene from functioning, or have no effect. Based on studies in the fly Drosophila melanogaster, it has been suggested that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70% of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial. Mutations can involve large sections of a chromosome becoming duplicated (usually by genetic recombination), which can introduce extra copies of a gene into a genome. Extra copies of genes are a major source of the raw material needed for new genes to evolve. This is important because most new genes evolve within gene families from pre-existing genes that share common ancestors. For example, the human eye uses four genes to make structures that sense light: three for colour vision and one for night vision; all four are descended from a single ancestral gene. New genes can be generated from an ancestral gene when a duplicate copy mutates and acquires a new function. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function. Other types of mutations can even generate entirely new genes from previously noncoding DNA. The generation of new genes can also involve small parts of several genes being duplicated, with these fragments then recombining to form new combinations with new functions.

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  1. Sex and recombination:

In asexual organisms, genes are inherited together, or linked, as they cannot mix with genes of other organisms during reproduction. In contrast, the offspring of sexual organisms contain random mixtures of their parents’ chromosomes that are produced through independent assortment. In a related process called homologous recombination, sexual organisms exchange DNA between two matching chromosomes. Recombination and reassortment do not alter allele frequencies, but instead change which alleles are associated with each other, producing offspring with new combinations of alleles. Sex usually increases genetic variation and may increase the rate of evolution.

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  1. Gene flow (genetic migration):

Gene flow is the exchange of genes between populations and between species. It can therefore be a source of variation that is new to a population or to a species. Migration, or gene flow, is defined in an evolutionary sense as “the transfer of alleles from the gene pool of one population to the gene pool of another population” (Freeman, Herron 225). Gene flow can be caused by the movement of individuals between separate populations of organisms, as might be caused by the movement of mice between inland and coastal populations, or the movement of pollen between heavy metal tolerant and heavy metal sensitive populations of grasses. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria. In medicine, this contributes to the spread of antibiotic resistance, as when one bacteria acquires resistance genes it can rapidly transfer them to other species.  Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean weevil Callosobruchus chinensis has occurred. An example of larger-scale transfers is the eukaryotic bdelloid rotifers, which have received a range of genes from bacteria, fungi and plants. Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains.  Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and bacteria, during the acquisition of chloroplasts and mitochondria. It is possible that eukaryotes themselves originated from horizontal gene transfers between bacteria and archaea.

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The presence or absence of gene flow fundamentally changes the course of evolution. Due to the complexity of organisms, any two completely isolated populations will eventually evolve genetic incompatibilities through neutral processes, as in the Bateson-Dobzhansky-Muller model, even if both populations remain essentially identical in terms of their adaptation to the environment. If genetic differentiation between populations develops, gene flow between populations can introduce traits or alleles which are disadvantageous in the local population and this may lead to organisms within these populations evolving mechanisms that prevent mating with genetically distant populations, eventually resulting in the appearance of new species. Thus, exchange of genetic information between individuals is fundamentally important for the development of the biological species concept.

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  1. Natural selection:

Natural selection is the process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent in the population over time. In natural selection, those variations in the genotype that increase an organism’s chances of survival and procreation are preserved and multiplied from generation to generation at the expense of less advantageous ones. Evolution often occurs as a consequence of this process. Natural selection may arise from differences in survival, in fertility, in rate of development, in mating success, or in any other aspect of the life cycle. All such differences result in natural selection to the extent that they affect the number of progeny an organism leaves.

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Figure above is representation of how natural selection occurs, from the appearance of a mutation to the change in a population.

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Natural selection has often been called a “self-evident” mechanism because it necessarily follows from three simple facts:

  • Variation exists within populations of organisms with respect to morphology, physiology, and behaviour (phenotypic variation).
  • Different traits confer different rates of survival and reproduction (differential fitness).
  • These traits can be passed from generation to generation (heritability of fitness).

More offspring are produced than can possibly survive, and these conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors are more likely to pass on their traits to the next generation than those with traits that do not confer an advantage. Evolution and natural selection are not the same thing. Evolution is change in the heritable characteristics of biological populations over successive generations. Natural selection is the phenomenon that rewards certain advantageous traits and punishes others through better or worse survival or reproduction. Natural selection thus is one of several forces that push evolution forward.

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The central concept of natural selection is the evolutionary fitness of an organism. Fitness is measured by an organism’s ability to survive and reproduce, which determines the size of its genetic contribution to the next generation. However, fitness is not the same as the total number of offspring: instead fitness is indicated by the proportion of subsequent generations that carry an organism’s genes. For example, if an organism could survive well and reproduce rapidly, but its offspring were all too small and weak to survive, this organism would make little genetic contribution to future generations and would thus have low fitness. If an allele increases fitness more than the other alleles of that gene, then with each generation this allele will become more common within the population. These traits are said to be “selected for.” Examples of traits that can increase fitness are enhanced survival and increased fecundity. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer—they are “selected against.”  Importantly, the fitness of an allele is not a fixed characteristic; if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful. However, even if the direction of selection does reverse in this way, traits that were lost in the past may not re-evolve in an identical form. However, a re-activation of dormant genes, as long as they have not been eliminated from the genome and were only suppressed perhaps for hundreds of generations, can lead to the re-occurrence of traits thought to be lost like hindlegs in dolphins, teeth in chickens, wings in wingless stick insects, tails and additional nipples in humans etc. “Throwbacks” such as these are known as atavisms.

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Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorised into three different types. The first is directional selection, which is a shift in the average value of a trait over time—for example, organisms slowly getting taller.  Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilising selection there is selection against extreme trait values on both ends, which causes a decrease in variance around the average value and less diversity. This would, for example, cause organisms to eventually have a similar height.

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A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates. Traits that evolved through sexual selection are particularly prominent among males of several animal species. Although sexually favoured, traits such as cumbersome antlers, mating calls, large body size and bright colours often attract predation, which compromises the survival of individual males. This survival disadvantage is balanced by higher reproductive success in males that show these hard-to-fake, sexually selected traits.

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Natural selection most generally makes ‘nature’ the measure against which individuals and individual traits, are more or less likely to survive. “Nature” in this sense refers to an ecosystem, that is, a system in which organisms interact with every other element, physical as well as biological, in their local environment. Eugene Odum, a founder of ecology, defined an ecosystem as: “Any unit that includes all of the organisms…in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity and material cycles (i.e.: exchange of materials between living and nonliving parts) within the system.”  Each population within an ecosystem occupies a distinct niche, or position, with distinct relationships to other parts of the system. These relationships involve the life history of the organism, its position in the food chain and its geographic range. This broad understanding of nature enables scientists to delineate specific forces which, together, comprise natural selection. Natural selection can act at different levels of organisation, such as genes, cells, individual organisms, groups of organisms and species.  Selection can act at multiple levels simultaneously. An example of selection occurring below the level of the individual organism is genes called transposons, which can replicate and spread throughout a genome. Selection at a level above the individual, such as group selection, may allow the evolution of cooperation.

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  1. Biased mutation:

In addition to being a major source of variation, mutation may also function as a mechanism of evolution when there are different probabilities at the molecular level for different mutations to occur, a process known as mutation bias. If two genotypes, for example one with the nucleotide G and another with the nucleotide A in the same position, have the same fitness, but mutation from G to A happens more often than mutation from A to G, then genotypes with A will tend to evolve.  Different insertion vs. deletion mutation biases in different taxa can lead to the evolution of different genome sizes.  Developmental or mutational biases have also been observed in morphological evolution. Mutation bias effects are superimposed on other processes. If selection would favor either one out of two mutations, but there is no extra advantage to having both, then the mutation that occurs the most frequently is the one that is most likely to become fixed in a population. Mutations leading to the loss of function of a gene are much more common than mutations that produce a new, fully functional gene. Most loss of function mutations are selected against. But when selection is weak, mutation bias towards loss of function can affect evolution.  For example, pigments are no longer useful when animals live in the darkness of caves, and tend to be lost.  This kind of loss of function can occur because of mutation bias, and/or because the function had a cost, and once the benefit of the function disappeared, natural selection leads to the loss. Loss of sporulation ability in Bacillus subtilis during laboratory evolution appears to have been caused by mutation bias, rather than natural selection against the cost of maintaining sporulation ability. When there is no selection for loss of function, the speed at which loss evolves depends more on the mutation rate than it does on the effective population size, indicating that it is driven more by mutation bias than by genetic drift. In parasitic organisms, mutation bias leads to selection pressures as seen in Ehrlichia. Mutations are biased towards antigenic variants in outer-membrane proteins.

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  1. Genetic drift:

Genetic drift is a change in the frequency of a population’s genes and alleles over time, often by founder effects (when a small group of individuals relocate) or bottlenecking (when a large population is decimated, leaving a smaller group to repopulate). That change occurs because alleles are subject to sampling error (i.e. random change).  As a result, when selective forces are absent or relatively weak, allele frequencies tend to “drift” upward or downward randomly (in a random walk). This drift halts when an allele eventually becomes fixed, either by disappearing from the population, or replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone. Even in the absence of selective forces, genetic drift can cause two separate populations that began with the same genetic structure to drift apart into two divergent populations with different sets of alleles. The time for a neutral allele to become fixed by genetic drift depends on population size, with fixation occurring more rapidly in smaller populations. It is usually difficult to measure the relative importance of selection and neutral processes, including genetic drift. The comparative importance of adaptive and non-adaptive forces in driving evolutionary change is an area of current research.

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  1. Genetic hitchhiking:

Recombination allows alleles on the same strand of DNA to become separated. However, the rate of recombination is low (approximately two events per chromosome per generation). As a result, genes close together on a chromosome may not always be shuffled away from each other and genes that are close together tend to be inherited together, a phenomenon known as linkage. This tendency is measured by finding how often two alleles occur together on a single chromosome compared to expectations, which is called their linkage disequilibrium. A set of alleles that is usually inherited in a group is called a haplotype. This can be important when one allele in a particular haplotype is strongly beneficial: natural selection can drive a selective sweep that will also cause the other alleles in the haplotype to become more common in the population; this effect is called genetic hitchhiking or genetic draft. Genetic draft caused by the fact that some neutral genes are genetically linked to others that are under selection can be partially captured by an appropriate effective population size. Genetic hitchhiking, also called genetic draft or the hitchhiking effect, is when an allele changes frequency not because it itself is under natural selection, but because it is near another gene that is undergoing a selective sweep and that is on the same DNA chain.

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  1. Adaptation:

Adaptation is the process that makes organisms better suited to their habitat.  Also, the term adaptation may refer to a trait that is important for an organism’s survival. For example, the adaptation of horses’ teeth to the grinding of grass. By using the term adaptation for the evolutionary process and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection. Adaptation may cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with genetic changes causing antibiotic resistance by both modifying the target of the drug, or increasing the activity of transporters that pump the drug out of the cell.

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Adaptation occurs through the gradual modification of existing structures. Consequently, structures with similar internal organisation may have different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are very similar to those in mice feet and primate hands, due to the descent of all these structures from a common mammalian ancestor.  However, since all living organisms are related to some extent, even organs that appear to have little or no structural similarity, such as arthropod, squid and vertebrate eyes, or the limbs and wings of arthropods and vertebrates, can depend on a common set of homologous genes that control their assembly and function; this is called deep homology. During evolution, some structures may lose their original function and become vestigial structures. Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely related species. Examples include pseudogenes, the non-functional remains of eyes in blind cave-dwelling fish, wings in flightless birds, the presence of hip bones in whales and snakes, and sexual traits in organisms that reproduce via asexual reproduction. Examples of vestigial structures in humans include wisdom teeth, the coccyx, the vermiform appendix, and other behavioural vestiges such as goose bumps and primitive reflexes. However, many traits that appear to be simple adaptations are in fact exaptations: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process. One example is the African lizard Holaspis guentheri, which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree—an exaptation. Within cells, molecular machines such as the bacterial flagella and protein sorting machinery evolved by the recruitment of several pre-existing proteins that previously had different functions. Another example is the recruitment of enzymes from glycolysis and xenobiotic metabolism to serve as structural proteins called crystallins within the lenses of organisms’ eyes.

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Adaptations can only occur if they are evolvable. Some adaptations which would prevent ill health are therefore not possible.

  • DNA cannot be totally prevented from undergoing somatic replication corruption; this has meant that cancer, which is caused by somatic mutations, has not (so far) been completely eliminated by natural selection.
  • Humans cannot biosynthesize vitamin C, and so risk scurvy, vitamin C deficiency disease, if dietary intake of the vitamin is insufficient.
  • Retinal neurons and their axon output have evolved to be inside the layer of retinal pigment cells. This creates a constraint on the evolution of the visual system such that the optic nerve is forced to exit the retina through a point called the optic disc. This, in turn, creates a blind spot. More importantly, it makes vision vulnerable to increased pressure within the eye (glaucoma) since this cups and damages the optic nerve at this point, resulting in impaired vision.

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  1. Co-evolution:

Interactions between organisms can produce both conflict and cooperation. When the interaction is between pairs of species, such as a pathogen and a host, or a predator and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called coevolution. An example is the production of tetrodotoxin in the rough-skinned newt and the evolution of tetrodotoxin resistance in its predator, the common garter snake. In this predator-prey pair, an evolutionary arms race has produced high levels of toxin in the newt and correspondingly high levels of toxin resistance in the snake. Other examples of co-evolution that you need to know are: Hummingbirds and the flowers that they feed on have co-evolved. The flower is pollinated when the hummingbird drinks its nectar. The flower attracts the hummingbird whilst the bird’s beak is curved to allow it to reach the nectar; the caterpillar of the Old World Swallowtail butterfly has evolved to be resistant to the chemical defences of the fringed rue plant. This means that the caterpillar can feed on the plant without being poisoned.

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  1. Cooperation:

Not all co-evolved interactions between species involve conflict.  Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the mycorrhizal fungi that grow on their roots and aid the plant in absorbing nutrients from the soil. This is a reciprocal relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending signals that suppress the plant immune system. Coalitions between organisms of the same species have also evolved. An extreme case is the eusociality found in social insects, such as bees, termites and ants, where sterile insects feed and guard the small number of organisms in a colony that are able to reproduce. On an even smaller scale, the somatic cells that make up the body of an animal limit their reproduction so they can maintain a stable organism, which then supports a small number of the animal’s germ cells to produce offspring. Here, somatic cells respond to specific signals that instruct them whether to grow, remain as they are, or die. If cells ignore these signals and multiply inappropriately, their uncontrolled growth causes cancer. Such cooperation within species may have evolved through the process of kin selection, which is where one organism acts to help raise a relative’s offspring. This activity is selected for because if the helping individual contains alleles which promote the helping activity, it is likely that its kin will also contain these alleles and thus those alleles will be passed on. Other processes that may promote cooperation include group selection, where cooperation provides benefits to a group of organisms.

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  1. Speciation:

There are multiple ways to define the concept of “species.” The choice of definition is dependent on the particularities of the species concerned. For example, some species concepts apply more readily toward sexually reproducing organisms while others lend themselves better toward asexual organisms. Despite the diversity of various species concepts, these various concepts can be placed into one of three broad philosophical approaches: interbreeding, ecological and phylogenetic. The Biological Species Concept (BSC) is a classic example of the interbreeding approach. Defined by Ernst Mayr in 1942, the BSC states that “species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups.” Despite its wide and long-term use, the BSC like others is not without controversy, for example because these concepts cannot be applied to prokaryotes, and this is called the species problem. Some researchers have attempted a unifying monistic definition of species, while others adopt a pluralistic approach and suggest that there may be different ways to logically interpret the definition of a species. Barriers to reproduction between two diverging sexual populations are required for the populations to become new species. Gene flow may slow this process by spreading the new genetic variants also to the other populations. Depending on how far two species have diverged since their most recent common ancestor, it may still be possible for them to produce offspring, as with horses and donkeys mating to produce mules. Such hybrids are generally infertile. In this case, closely related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. This is because during meiosis the homologous chromosomes from each parent are from different species and cannot successfully pair. However, it is more common in plants because plants often double their number of chromosomes, to form polyploids. This allows the chromosomes from each parental species to form matching pairs during meiosis, since each parent’s chromosomes are represented by a pair already. The importance of hybridisation in producing new species of animals is unclear, although cases have been seen in many types of animals, with the gray tree frog being a particularly well-studied example. Speciation has been observed multiple times under both controlled laboratory conditions and in nature. In sexually reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry, agriculture, or laboratory experiments. Whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion.

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  1. Extinction:

Extinction is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation and disappear through extinction.  Nearly all animal and plant species that have lived on Earth are now extinct, and extinction appears to be the ultimate fate of all species. These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass extinction events. The Cretaceous–Paleogene extinction event, during which the non-avian dinosaurs became extinct, is the most well-known, but the earlier Permian–Triassic extinction event was even more severe, with approximately 96% of all marine species driven to extinction. The Holocene extinction event is an ongoing mass extinction associated with humanity’s expansion across the globe over the past few thousand years. Present-day extinction rates are 100–1000 times greater than the background rate and up to 30% of current species may be extinct by the mid-21st century. Human activities are now the primary cause of the ongoing extinction event; global warming may further accelerate it in the future.

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The role of extinction in evolution is not very well understood and may depend on which type of extinction is considered. The causes of the continuous “low-level” extinction events, which form the majority of extinctions, may be the result of competition between species for limited resources (the competitive exclusion principle). If one species can out-compete another, this could produce species selection, with the fitter species surviving and the other species are driven to extinction. The intermittent mass extinctions are also important, but instead of acting as a selective force, they drastically reduce diversity in a nonspecific manner and promote bursts of rapid evolution and speciation in survivors.

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Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its environment will not survive and will become extinct. Here are some of the factors that can cause a species to become extinct:

  • changes to the environment, such as a change in climate
  • new diseases
  • new predators
  • new competitors

The fossil record shows that many species have become extinct since life on Earth began. Extinction is still happening and a lot of it occurs because of human activities. We compete with other living things for space, food and water, and we are very successful predators.

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When humans faced extinction:

Humans may have come close to extinction about 70,000 years ago, according to the latest genetic research. The study suggests that at one point there may have been only 2,000 individuals alive as our species teetered on the brink. This means that, for a while, humanity was in a perilous state, vulnerable to disease, environmental disasters and conflict. If any of these factors had turned against us, we would not be here. The small genetic diversity of modern humans indicates that at some stage during the last 100,000 years, the human population dwindled to a very low level.  It was out of this small population, with its consequent limited genetic diversity, that today’s humans descended.

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Neanderthals went Extinct:

Neanderthals emerged in Europe around 400,000 years ago. They began crossing paths 300,000 years later, as humans made their way into Neanderthal territory. Eventually, these encounters became more and more common and, for between 10,000 and 15,000 years, the two species co-existed and interbred—2 percent of our DNA comes from Neanderthals. Around 38,000 years ago, Neanderthals went extinct. Over recent decades two main theories of what caused their demise have emerged. The first is climate change—their decline coincides with a period of extreme cold in Western Europe that would have placed a huge amount of stress on the species. The other is competition with modern humans—our bigger brains and better adaptations to the environment at the time meant Neanderthals didn’t have a chance. The predominant theory is that early humans killed off the Neanderthal through competition for food and habitat. Homo sapiens’ superior brain power and hunting techniques meant the Neanderthals couldn’t compete. These two factors are not mutually exclusive and it is often suggested a combination of the two led to their downfall. Kolodny and Feldman’s new model says that irrespective of climate change and humans being at an evolutionary advantage, Neanderthals were always going to go extinct. Neanderthals did not go extinct because of climate change and competition with modern humans—they were doomed to be wiped out as a result of the evolutionary phenomenon of “random species drift.” As a result of “species drift,” humans slowly replaced Neanderthals until they dominated the landscape. This replacement, the researchers say, “was certain to occur, even in a selectively neutral setting, given the estimated migration pattern near the onset of the interaction between the two populations,” the researchers wrote.

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The geologic time scale (GTS):

The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth’s history. The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic. The first three of these can be referred to collectively as the Precambrian supereon. Eons are divided into eras, which are in turn divided into periods, epochs and ages.

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The above four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. Therefore, the second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, and the most recent period is expanded in the fourth timeline.

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Epoch:

In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age but shorter than a period. The current epoch is the Holocene Epoch of the Quaternary Period as seen in the table below. Epochs are most commonly used for the younger Cenozoic Era, where a greater collection of fossils has been found and paleontologists have more detailed knowledge of the events that occurred during those times. They are less commonly referred to for the other eras and eons, since less fossil evidence exists that allows us to form a clearer view of those time periods.

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Eon Era Period Epoch Major events Start, million years ago
Phanerozoic Cenozoic Quaternary Holocene Quaternary Ice Age recedes, and the current interglacial begins. Sahara forms from savannah. Rise of human civilization, beginning of agriculture. Stone Age cultures give way to Bronze Age (3300 BC) and Iron Age (1200 BC), giving rise to many pre-historic cultures throughout the world. Little Ice Age (stadial) causes brief cooling in Northern Hemisphere from 1400 to 1850. Following the Industrial Revolution, atmospheric CO2 levels rise from around 280 parts per million (ppm) to the current level of 410 ppm. 0.0117
Pleistocene Flourishing and then extinction of Pleistocene megafauna. Evolution of anatomically modern humans. Quaternary Ice Age continues with glaciations and interstadials (and the accompanying fluctuations from 100 to 300 ppm in atmospheric CO2 levels), further intensification of Icehouse Earth conditions, roughly 1.6 Ma. Last glacial maximum (30000 years ago), last glacial period (18000–15000 years ago). Dawn of human stone-age cultures, with increasing technical complexity relative to previous ice age cultures, such as engravings and clay statues (e.g. Venus of Lespugue), particularly in the Mediterranean and Europe. Lake Toba supervolcano erupts 75000 years before present, causing a volcanic winter that possibly pushes humanity to the brink of extinction. Pleistocene ends with Oldest Dryas, Older Dryas/Allerød and Younger Dryas climate events, with Younger Dryas forming the boundary with the Holocene. 0.126
0.781
1.8
2.58
Neogene Pliocene Intensification of present Icehouse conditions, present (Quaternary) ice age begins roughly 2.58 Ma; cool and dry climate. Australopithecines, many of the existing genera of mammals, and recent mollusks appear. Homo habilis appears. 3.6
5.333

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The current epoch Holocene is not seen in the figure below. Epoch preceding Holocene epoch are on the left side and number of years BP are on the right side.

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BP:

Before Present (BP) years is a time scale used mainly in geology and other scientific disciplines to specify when events occurred in the past. Because the “present” time changes, standard practice is to use 1 January 1950 as the commencement date of the age scale, reflecting the origin of practical radiocarbon dating in the 1950s.

Traditionally, geologists have used different abbreviations for ages (time before present) and duration (amount of time elapsing between two different events). Ages are abbreviated from Latin: Ga (giga-annum) is a billion years, Ma (mega-annum) is a million years, Ka (kilo-annum) is a thousand years. Duration, on the other hand, has been abbreviated from “years.”

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Various disciplines associated with evolution:

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Anthropology:

Anthropology is the study of various aspects of humans within past and present societies. Social anthropology and cultural anthropology study the norms and values of societies. Linguistic anthropology studies how language affects social life. Biological or physical anthropology studies the biological development of humans.

Archaeology, which studies past human cultures through investigation of physical evidence, is thought of as a branch of anthropology in the United States, while in Europe, it is viewed as a discipline in its own right or grouped under other related disciplines, such as history.

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Evolutionary anthropology:

Evolutionary anthropology is the interdisciplinary study of the evolution of human physiology and human behaviour and the relation between hominids and non-hominid primates. Evolutionary anthropology is based in natural science and social science. Evolutionary anthropology is concerned with both biological and cultural evolution of humans, past and present. It is based on a scientific approach, and brings together fields such as archaeology, behavioral ecology, psychology, primatology, and genetics. It is a dynamic and interdisciplinary field, drawing on many lines of evidence to understand the human experience, past and present. Note that cultural evolution is not the same as biological evolution, and that human culture involves the transmission of cultural information, which behaves in ways quite distinct from human biology and genetics. The study of cultural change is increasingly performed through cladistics and genetic models.

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Paleontology:

Paleontology is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch (roughly 11,700 years before present). It includes the study of fossils to determine organisms’ evolution and interactions with each other and their environments (their paleoecology). Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier’s work on comparative anatomy, and developed rapidly in the 19th century. Paleontology lies on the border between biology and geology, but differs from archaeology in that it excludes the study of anatomically modern humans. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics, and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3.8 billion years ago. As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates.

Paleontology is key to the study of evolution for two reasons.

  1. The discovery of fossils showing forms of animals that had never previously been seen began to cast serious doubt upon creationist theories.
  2. Fossils provide the only direct evidence of the history of evolution.

Today, whereas molecular biology might be used to study microevolution, or the development of individual species, paleontology is used to study Macroevolution, or large evolutionary trends.

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Paleoanthropology:

The modern scientific study of human evolution is called paleoanthropology. A subfield of anthropology, this discipline searches for the roots of human physical traits, culture, and behavior. It attempts to answer questions: What makes us human? When and why did we begin to walk upright? How did our brains, language, art, music, and religion develop? By approaching these questions from a variety of directions, using information learned from other disciplines such as molecular biology, paleontology, archaeology, sociology, and biology, we continue to increase knowledge of our evolutionary origins. Paleoanthropology seeks to understand the early development of anatomically modern humans, a process known as hominization, through the reconstruction of evolutionary kinship lines within the family Hominidae, working from biological evidence (such as petrified skeletal remains, bone fragments, footprints) and cultural evidence (such as stone tools, artifacts, and settlement localities). The field draws from and combines paleontology, biological anthropology, and cultural anthropology. As technologies and methods advance, genetics plays an ever-increasing role, in particular to examine and compare DNA structure as a vital tool of research of the evolutionary kinship lines of related species and genera.

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Early human fossils and archeological remains offer the most important clues about this ancient past. These remains include bones, tools and any other evidence (such as footprints, evidence of hearths, or butchery marks on animal bones) left by earlier people. Usually, the remains were buried and preserved naturally. They are then found either on the surface (exposed by rain, rivers, and wind erosion) or by digging in the ground. By studying fossilized bones, scientists learn about the physical appearance of earlier humans and how it changed. Bone size, shape, and markings left by muscles tell us how those predecessors moved around, held tools, and how the size of their brains changed over a long time. Archeological evidence refers to the things earlier people made and the places where scientists find them. By studying this type of evidence, archeologists can understand how early humans made and used tools and lived in their environments. Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the “jigsaw puzzles” of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary “family trees”. The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. Despite advances in molecular biology, more traditional sciences of palaeontology and archaeology are very much alive, invigorated by better dating and new tools such as isotopic analysis. Major fossil finds, such as Ardipithecus ramidus, Australopithecus sediba, and Homo naledi, all from Africa, plus Homo erectus bones from Africa and Asia, have broadened our view of the ancient branches of the human lineage.

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A timeline of scientific study of evolution:

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The 1800s to 1890s

1809 – Jean Baptiste de Lamarck (1744-1829) publishes Philosophie Zoologique

Lamarck was one of the first to propose a theory about evolution. He believed that as animals tried to fit into their environment, their efforts produced a bodily change that was then passed on to their offspring. While a popular theory at the time, it was later disproved by Darwin’s ideas about natural selection. One of the classic images used to describe Lamark’s theory of evolution is of the giraffe’s neck. Giraffes needed to stretch their necks in order to reach food in taller trees. This effort resulted in longer necks, a feature passed on to the offspring.

1833 – Charles Lyell (1797-1875) and Principles of Geology

The work of Charles Lyell provided the foundation for the study of modern geology and an essential context to Darwin’s ideas about evolutionary change. The realisation that the world was older than previously thought did much to establish one of the significant beliefs formed in the 19th century – the antiquity of humans.

1859 – Charles Darwin (1809-1882) publishes On the Origin of Species

Darwin was not the first to think of evolution, but he was the first to propose a sound scientific theory supported by a huge amount of evidence. Although he formulated his theory while acting as a naturalist on the HMS Beagle from 1831-1836, his concerns about the implications of releasing such a theory led him to delay its announcement for over 20 years. He may have delayed further if not alerted to the work of Alfred Wallace, another British naturalist who had independently come up with a theory on evolution by natural selection. Darwin and Wallace co-announced their theory to the Linnaean Society of London in 1858 and Darwin then published his work On the Origin of Species the following year. This theory was widely misunderstood and mocked by a society which had been taught by the predominant religions of the day that species were created individually by God and unchangeable. Many decades would pass before the theory gained general acceptance. Darwin’s theory is still accepted today, although somewhat modified, and forms the basis of modern evolutionary theory.

1863 – Thomas Huxley (1825-1895) publishes Evidence as to Man’s Place in Nature’ in defence of Darwin

1871 – Darwin publishes The Descent of Man

This publication, released in 1871, contained the detailed ideas regarding human evolution that Darwin had not discussed in On the Origin of Species. Although written without a single pre-human fossil as evidence, he predicted that humans originated in Africa. It would take over half a century before he would be proven correct. “In each great region of the world the living mammals are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man’s nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.”

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The 1900s to 1940s

1900 – Rediscovery of Gregor Mendel’s breeding experiments (published in 1866) and the formation of the Principles of Inheritance

The Austrian monk Gregor Mendel (1822-1884) discovered that hereditary particles (given the name ‘genes’ in 1909) pass traits from a parent to the offspring. The appearance of the offspring is determined by these genes, not by a ‘blending’ of characteristics as was believed. The work revealed to biologists how evolution worked at the molecular level and provided the scientific basis for variation that Darwin had been unable to explain. Darwin’s original theory could now be modified and adapted to fit in with this new evidence.

1942 – Julian Huxley publishes The Modern Synthesis

Huxley’s work outlined the role of genetics and ecology in natural selection. He believed that these operated at the core of evolutionary change, an idea that became widely accepted.

1947 – American chemist Willard Libby introduced his work on carbon-14 dating

This discovery revolutionised science, particularly in the fields of human studies. It was first used to provide accurate dates of up to 40,000 years old on European sites. New techniques would soon be developed that worked on the same principles of radioactive decay in other elements and would prove to be more useful in dating older sites.

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The 1950s to now

1953 – James Watson and Francis Crick reveal how genes are inherited with their discovery of the double helix shape of DNA.

1960s – Introduction of biochemistry to the field of human evolution

Prior to the 1960s, anthropologists believed that the common ancestor of humans and apes lived about 15 million years ago. This placed humans at a comfortable distance from their closest living relatives, and hence from the entire animal kingdom. The scientific advances in the 1960s would change all of this. Biochemists discovered that they were able to compare the molecules of apes and humans, providing a more accurate measurement of relatedness. The results showed that there were only very small differences between these molecules and that this reflected only a short amount of time since apes and humans diverged from a common ancestor. The differences between the molecules are caused by mutations in DNA. Knowing the approximate rate at which mutations occur, scientists were able to calculate that the human-line split from the ape-line only five to seven million years ago. This created huge controversy at the time between biologists and anthropologists, a controversy which raged for over a decade before further studies supported the claims of the biochemists. Today no one doubts our close genetic relationship to the other living apes.

1980s – Improved technology, such as CT scans, MRIs (magnetic resonance imaging) and DNA analysis, allows scientists to develop new methods of interpreting fossils.

The study of human evolution has become a multi-disciplinary field.

2003 – Completion of The Human Genome Project (with final papers published in 2006)

This landmark project identified all the approximately 20,000-25,000 genes in human DNA and determined the sequences of the 3 billion chemical base pairs that make up the DNA. From an evolutionary perspective, this project helps identify what makes us human, how we are related to other organisms and what part of our DNA has changed or mutated over time.

2009 – First draft of the Neanderthal genome announced

Comparing the human and Neanderthal genomes with that of our closest living relative, the chimpanzee, may reveal which genes changed very recently giving modern humans an edge over Neanderthals.

2010 – Publication of the first detailed analysis of the Neanderthal genome

Of key importance was the discovery that Europeans and Asians share 1-4% of their DNA with Neanderthals but Africans do not (previous studies on the mtDNA showed no signs of interbreeding between the species). This suggests modern humans and Neanderthals interbred after moderns left Africa and before they spread to Europe and Asia – the most likely location was the Levant, an area both species occupied about 80,000 years ago.

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Charles Darwin:

The founder of the modern theory of evolution was Charles Darwin. The son and grandson of physicians, he enrolled as a medical student at the University of Edinburgh. After two years, however, he left to study at the University of Cambridge and prepare to become a clergyman. He was not an exceptional student, but he was deeply interested in natural history. On December 27, 1831, a few months after his graduation from Cambridge, he sailed as a naturalist aboard the HMS Beagle on a round-the-world trip that lasted until October 1836. Darwin was often able to disembark for extended trips ashore to collect natural specimens. The discovery of fossil bones from large extinct mammals in Argentina and the observation of numerous species of finches in the Galapagos Islands were among the events credited with stimulating Darwin’s interest in how species originate. In 1859 he published On the Origin of Species by Means of Natural Selection, a treatise establishing the theory of evolution and, most important, the role of natural selection in determining its course. He published many other books as well, notably The Descent of Man and Selection in Relation to Sex, which extends the theory of natural selection to human evolution.

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The possibility of linking humans with earlier apes by descent became clear only after 1859 with the publication of Charles Darwin’s On the Origin of Species, in which he argued for the idea of the evolution of new species from earlier ones. Darwin’s book did not address the question of human evolution, saying only that “Light will be thrown on the origin of man and his history.” The first debates about the nature of human evolution arose between Thomas Henry Huxley and Richard Owen. Huxley argued for human evolution from apes by illustrating many of the similarities and differences between humans and apes, and did so particularly in his 1863 book Evidence as to Man’s Place in Nature. However, many of Darwin’s early supporters (such as Alfred Russel Wallace and Charles Lyell) did not initially agree that the origin of the mental capacities and the moral sensibilities of humans could be explained by natural selection, though this later changed. Darwin applied the theory of evolution and sexual selection to humans when he published The Descent of Man in 1871. Darwin’s books, On the Origins of the Species by Natural Selection (1859) and The Descent of Man (1871), expressed his theory of evolution and revolutionized the study of life and human origins. Darwin presented evidence showing that natural species including humans have changed, or evolved, over long spans of time. He also argued that radically new forms of life develop from existing species. He noted that all organisms compete with one another for food, space, mates, and other things needed for survival and reproduction. The most successful individuals in this competition have the greatest chance of reproducing and passing these characteristics on to offspring. Over hundreds of thousands of generations, one form of life can evolve into one or more other forms. Darwin called this process natural selection. The theory of evolution by natural selection, first formulated in Darwin’s book “On the Origin of Species” in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.  Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology. The theory has two main points, said Brian Richmond, curator of human origins at the American Museum of Natural History in New York City. “All life on Earth is connected and related to each other,” and this diversity of life is a product of “modifications of populations by natural selection, where some traits were favored in and environment over others,” he said. More simply put, the theory can be described as “descent with modification,” said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution National Museum of Natural History in Washington, D.C., who specializes in the study of human origins. The theory is sometimes described as “survival of the fittest,” but that can be misleading, Pobiner said. Here, “fitness” refers not to an organism’s strength or athletic ability, but rather the ability to survive and reproduce. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called “microevolution.” But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as “macroevolution.” It can turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into humans.

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Darwin’s theory of evolution is based on key facts and the inferences drawn from them, which biologist Ernst Mayr summarised as follows:

  • Every species is fertile enough that if all offspring survived to reproduce, the population would grow (fact).
  • Despite periodic fluctuations, populations remain roughly the same size (fact).
  • Resources such as food are limited and are relatively stable over time (fact).
  • A struggle for survival ensues (inference).
  • Individuals in a population vary significantly from one another (fact).
  • Much of this variation is heritable (fact).
  • Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection (fact).
  • This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).

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The most serious difficulty facing Darwin’s evolutionary theory was the lack of an adequate theory of inheritance that would account for the preservation through the generations of the variations on which natural selection was supposed to act. Darwin didn’t know anything about genetics. He observed the pattern of evolution, but he didn’t really know about the mechanism. The missing link in Darwin’s argument was provided by Mendelian genetics. About the time the Origin of Species was published, the Augustinian monk Gregor Mendel was starting a long series of experiments with peas in the garden of his monastery in Brünn, Austria-Hungary (now Brno, Czech Republic). These experiments and the analysis of their results are by any standard an example of masterly scientific method. Mendel’s paper, published in 1866 in the Proceedings of the Natural Science Society of Brünn, formulated the fundamental principles of the theory of heredity that is still current. His theory accounts for biological inheritance through particulate factors (now known as genes) inherited one from each parent, which do not mix or blend but segregate in the formation of the sex cells, or gametes. Mendel’s discoveries remained unknown to Darwin, however, and, indeed, they did not become generally known until 1900, when they were simultaneously rediscovered by a number of scientists on the Continent. The rediscovery in 1900 of Mendel’s theory of heredity, by the Dutch botanist and geneticist Hugo de Vries and others, led to an emphasis on the role of heredity in evolution.  A major breakthrough came in 1937 with the publication of Genetics and the Origin of Species by Theodosius Dobzhansky, a Russian-born American naturalist and experimental geneticist. Dobzhansky’s book advanced a reasonably comprehensive account of the evolutionary process in genetic terms, laced with experimental evidence supporting the theoretical argument. Genetics and the Origin of Species may be considered the most important landmark in the formulation of what came to be known as the synthetic theory of evolution, effectively combining Darwinian natural selection and Mendelian genetics. It had an enormous impact on naturalists and experimental biologists, who rapidly embraced the new understanding of the evolutionary process as one of genetic change in populations. Interest in evolutionary studies was greatly stimulated, and contributions to the theory soon began to follow, extending the synthesis of genetics and natural selection to a variety of biological fields. The main writers who, together with Dobzhansky, may be considered the architects of the synthetic theory were the German-born American zoologist Ernst Mayr, the English zoologist Julian Huxley, the American paleontologist George Gaylord Simpson, and the American botanist George Ledyard Stebbins. These researchers contributed to a burst of evolutionary studies in the traditional biological disciplines and in some emerging ones—notably population genetics and, later, evolutionary ecology. By 1950 acceptance of Darwin’s theory of evolution by natural selection was universal among biologists, and the synthetic theory had become widely adopted.

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Modern understanding:

The most important line of investigation after 1950 was the application of molecular biology to evolutionary studies. In 1953 the American geneticist James Watson and the British biophysicist Francis Crick deduced the molecular structure of DNA (deoxyribonucleic acid), the hereditary material contained in the chromosomes of every cell’s nucleus. The genetic information is encoded within the sequence of nucleotides that make up the chainlike DNA molecules. This information determines the sequence of amino acid building blocks of protein molecules, which include, among others, structural proteins such as collagen, respiratory proteins such as hemoglobin, and numerous enzymes responsible for the organism’s fundamental life processes. Genetic information contained in the DNA can thus be investigated by examining the sequences of amino acids in the proteins. The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes. Such changes are called mutations. Mutations are basically the raw material on which evolution acts.  Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage. Most times, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism.  If so, it will become more prevalent in the next generation and spread throughout the population.  In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. Mutations are random, but selection for them is not random. But natural selection isn’t the only mechanism by which organisms evolve. For example, genes can be transferred from one population to another when organisms migrate or immigrate, a process known as gene flow. And the frequency of certain genes can also change at random, which is called genetic drift. Modern science now understands that the mechanism for evolutionary change resides in genes, the basic building block of heredity. Genes determine how the body, and often the behavior, of an organism will develop over the course of its life. Certain information in genes can change, and over time this genetic change can actually alter a species’ overall way of life. Scientists estimate that our human ancestors began to diverge from the African primates between eight million and five million years ago. This figure is the result of studying the genetic makeup of humans and apes, and then calculating approximately how long it took for those differences to develop. Using similar methods of comparing genetic variation among human populations around the world, it is thought that all people living today share a common genetic ancestor.

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The Ancestor’s Tale:

The Ancestor’s Tale: A Pilgrimage to the Dawn of Life is a 2004 popular science book by Richard Dawkins, with contributions from Dawkins’ research assistant Yan Wong. It follows the path of humans backwards through evolutionary history, meeting humanity’s cousins as they converge on common ancestors. He talks about our universe that has its own remarkable set of laws and constants which are capable of generating us and other organisms living on this planet. Not only it is capable of generating organisms, it is capable of evolving them too. He claims that biological evolution has no privilege line of descent and no designated end. Evolution has arrived at many millions of interim ends and organisms are still evolving. He believes that evolution is directional, progressive and even predictable. He also talks about how Homo sapiens tend to think that they are more evolved than other, but that’s not true, all the other species have gone through evolution too. They just have inherited different traits that helped them survive through natural selection. Dawkins claims that all species are equal. He uses backward chronology, instead of forward chronology because in backward chronology, no matter where you start, you end up celebrating the unity of life. While going forward just extols diversity. This book is a pilgrimage to discover human ancestors and as it progresses, it meets other pilgrims (organisms) who join humans in order as the book reaches the common ancestor that human share with them. Every newly recruited species, genus or family has its own peculiar features, often ones that are relevant to human anatomy or otherwise interesting for humans. For instance, Dawkins discusses why the axolotl never needs to grow up, how new species come about, how hard it is to classify animals, and why our fish-like ancestors moved to the land. These peculiar features are studied and analysed using a newly introduced tool or method from evolutionary biology, carefully woven into a tale to illustrate how the Darwinian theory of evolution explains all diversity in nature. Even though the book is best read sequentially, every chapter can also be read independently as a self-contained tale with an emphasis on a particular aspect of modern biology. As a whole, the book elaborates on all major topics in evolution.

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Classifying current and ancient organisms:

Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names. Linnaean taxonomy is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. For example: it is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order; this is important since the Linnaean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed.

Figure above shows levels in the Linnaean taxonomy.

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Our place in the animal kingdom:

Humans possess many unique characteristics but we also share a number of similarities with other animals. These similarities and differences are revealed through our genetic make-up, the ways our bodies are constructed and our behaviour. They help us to understand our place in the animal kingdom by allowing us to work out the evolutionary relationships between ourselves and other animals. Studies of our closest living relatives, the apes, also provide valuable clues about our early ancestors’ bodies and lifestyles.

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Humans are mammals:

Humans are members of a large group of animals known as mammals (Class Mammalia). The first mammals evolved about 190 million years ago. These early mammals were small, insect-eating creatures that lived at the same time as the dinosaurs. When the dinosaurs disappeared about 65 million years ago, mammals began to diversify into many forms. There are now about 4500 different species of mammals living in almost every environment on earth including the oceans, fresh water, on and below the ground, in the treetops and even in the sky.

Mammal features:

All mammals (including humans) have the same distinctive features. These include:

  • fur or hair growing from the skin
  • mammary glands that, in females, produce milk for feeding the young
  • three bones (the malleus, incus and stapes) in the middle ear for transmitting sound to the inner ear
  • a single bone (the dentary) on each side of the lower jaw

Humans are classified as mammals because humans have the same distinctive features (listed above) found in all members of this large group.

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Phylogeny, the study of the ancestry (pattern and history) of organisms, yields a phylogenetic tree to show relatedness between species (or a cladogram in other taxonomic disciplines).

Cladogram above shows relationship between mammalian species. A cladogram is a diagram used in cladistics to show relations among organisms. Cladistics is an approach to biological classification in which organisms are categorized in groups (“clades”) based on the most recent common ancestor.

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Mammals developed from primitive mammal-like reptiles during the Triassic Period, some 200-245 million years ago. After the terminal Cretaceous extinction (65 million years ago) eliminated the dinosaurs, mammals as one of the surviving groups, underwent an adaptive radiation during the Tertiary Period. The major orders of mammals developed at this time, including the Primates to which humans belong. The first primates appeared more than 60 million years ago.

Many different types of primates have evolved over this vast period of time and many of these no longer exist. Others have survived and there are now more than 350 different species of living primates. Almost all of today’s primates live in tropical and subtropical areas of Africa, Madagascar, Asia, Central America and South America. They include lemurs, lorises, tarsiers, monkeys and apes are all primates.

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Primate features:

Primates (including humans) are different to all other animals because they are the only mammals that have the following combination of features:

  • relatively large, complex brain
  • forward-facing eyes with overlapping fields of view that allow depth perception
  • eye sockets with a ring or cup of bone surrounding and supporting the eyes
  • grasping hands with long fingers to curl around objects
  • opposable thumbs and/or big toes (able to touch the other digits on the same hand or foot)
  • flat nails (rather than claws) on some fingers and toes
  • sensitive pads under the tips of the fingers and toes containing special touch receptors called Meissner’s Corpuscles
  • a well-developed collarbone (clavicle)
  • two nipples (but sometimes more) on the chest (in females, these supply milk to the young)
  • penis and testes that permanently hang down from the body (in males)
  • long childhood that extends well beyond weaning

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Humans are primates:

Humans are members of a particular sub-group of mammals known as the primates (Order Primates).

Humans are classified within the subgroup of primates called apes and in particular the ‘Great Apes’.

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Hominoids are a primate superfamily, the hominid family is considered to comprise both the great ape lineages and human lineages within the hominoid superfamily. The Hominidae, whose members are known as great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera:

Figure above is family tree showing the extant hominoids: humans (genus Homo), chimpanzees and bonobos (genus Pan), gorillas (genus Gorilla), orangutans (genus Pongo), and gibbons (four genera of the family Hylobatidae: Hylobates, Hoolock, Nomascus, and Symphalangus). All except gibbons are hominids.

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Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Thus human evolution is the study of the lineage, or clade, comprising species more closely related to modern humans than to chimpanzees. Its stem species is the so-called ‘common hominin ancestor’, and its only extant member is Homo sapiens. This clade contains all the species more closely-related to modern humans than to any other living primate. Until recently, these species were all subsumed into a family, Hominidae, but this group is now more usually recognised as a tribe, the Hominini. Paleontologists generally use approaches based on cladistics, a technique for working out the evolutionary “family tree” of a set of organisms. It works by the logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters that are compared may be anatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or proteins. The result of a successful analysis is a hierarchy of clades – groups that share a common ancestor. Ideally the “family tree” has only two branches leading from each node (“junction”), but sometimes there is too little information to achieve this and paleontologists have to make do with junctions that have several branches. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes, evolved more than once, so this must be taken into account in analyses.

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The terminology of the immediate biological family is currently in flux. Over time, biological classifications change due to improved techniques and better knowledge about the biology and the evolutionary relationships of different living things. Now, with their better knowledge, scientists have revised their classifications to develop more up-to-date evolutionary trees. In this scheme, only two families are recognised with all the Great Apes (including humans) placed into the same family, the Hominidae or hominids. The next branching of this evolutionary tree divides the orang-utans into one subfamily and all the remaining Great Apes into another subfamily. Then at the tribe level, gorillas, chimpanzees and humans separate onto different branches of the evolutionary tree with humans in the Hominini or hominin branch. As a result of this classification change, modern humans and all our extinct ancestors on our own branch of the evolutionary tree are now known as hominins rather than as hominids as they were formerly known in old classifications. The term “hominin” refers to any genus in the human tribe (Hominini), of which Homo sapiens (modern man) is the only living specimen. The term “African apes” refers only to chimpanzees and gorillas. The word homo, the name of the biological genus to which humans belong, is Latin for “human”. It was chosen originally by Carl Linnaeus in his classification system. The word “human” is from the Latin humanus, the adjectival form of homo. .”Sapiens” means “thought”. Homo sapiens means “the thinking man”.  Linnaeus and other scientists of his time also considered the great apes to be the closest relatives of humans based on morphological and anatomical similarities.

The most commonly used recent definitions are:

Hominid – the group consisting of all modern and extinct Great Apes (that is, modern humans, chimpanzees, gorillas and orang-utans plus all their immediate ancestors).

Hominin – the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).

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The timeline of human evolution spans approximately 7 million years, from the separation of the Pan genus until the emergence of behavioral modernity by 50,000 years ago. The first 3 million years of this timeline concern Sahelanthropus, the following 2 million concern Australopithecus and the final 2 million span the history of the Homo genus in the Paleolithic era.

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Evidence from the fossil record and from a comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately 6 million years ago. Several species evolved from the evolutionary branch that includes humans, although our species is the only surviving member. The term hominin is used to refer to those species that evolved after this split of the primate line, thereby designating species that are more closely related to humans than to chimpanzees. Hominins were predominantly bipedal and include those groups that likely gave rise to our species—including Australopithecus, Homo habilis, and Homo erectus—and those non-ancestral groups that can be considered “cousins” of modern humans, such as Neanderthals. Determining the true lines of descent in hominins is difficult. In years past, when relatively few hominin fossils had been recovered, some scientists believed that considering them in order, from oldest to youngest, would demonstrate the course of evolution from early hominins to modern humans. In the past several years, however, many new fossils have been found, and it is clear that there was often more than one species alive at any one time and that many of the fossils found (and species named) represent hominin species that died out and are not ancestral to modern humans. The evolutionary tree below shows the relationship between humans and the great apes. All great apes, including baboons, gibbons, orangutans, gorillas, chimpanzees, humans, and human ancestors, belong in the superfamily Hominoidea. Of these great apes, all but baboons and gibbons belong in the family Hominidae. Gorillas, chimpanzees, humans, and human ancestors belong in the subfamily Homininae. Humans and their direct ancestors belong in the tribe Hominini.

 

Figure above shows the evolution of modern humans. A human is a member of the genus Homo, of which Homo sapiens is the only extant species, and within that Homo sapiens sapiens is the only surviving subspecies. Homo sapiens sapiens are humans living on earth for last 10,000 years. All of us are homo sapiens sapiens.

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Vanity of humans:

Humans share 96 % of their genetic material with the common chimpanzee, which means that chimps should probably be grouped with humans in the family Hominidae and genus Homo rather than in genus Pan where they are now placed along with the genus Pongo (orangutans) and genus Gorrilla. Because chimpanzees are genetically closer to humans than the other two great apes, only the vanity of humans keeps them out of Homo.

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Taxonomy of Homo sapiens:

One of several possible lines of descent, or taxonomic ranking, of Homo sapiens is shown below.

Rank Name Common name Millions of years ago
Domain Eukaryota Cells with a nucleus 2,100
Kingdom Animalia Animals 590
Phylum Chordata Chordates (Vertebrates and closely related invertebrates) 530
Subphylum Vertebrata Vertebrates 505
Superclass Tetrapoda Tetrapods (animals with four limbs) 395
(unranked clade) Amniota Amniotes (fully terrestrial tetrapods whose eggs are “equipped with an amnios”) 340
Clade Synapsida Proto-Mammals 308
Class Mammalia Mammals 220
Subclass Theria Mammals that give birth to live young (i.e., non-egg-laying) 160
Infraclass Eutheria Placental mammals (i.e., non-marsupials) 125
Magnorder Boreoeutheria Supraprimates, (most) hoofed mammals, (most) carnivorous mammals, whales, and bats 124–101
Superorder Euarchontoglires Supraprimates: primates, colugos, tree shrews, rodents, and rabbits 100
Grandorder Euarchonta Primates, colugos, and tree shrews 99–80
Mirorder Primatomorpha Primates and colugos 79.6
Order Primates Primates 75
Suborder Haplorrhini “Dry-nosed” (literally, “simple-nosed”) primates: apes, monkeys, and tarsiers 63
Infraorder Simiiformes “Higher” primates (Simians): apes and monkeys 40
Parvorder Catarrhini “Downward-nosed” primates: apes and old-world monkeys 30
Superfamily Hominoidea Apes: great apes and lesser apes (gibbons) 28
Family Hominidae Great apes: humans, chimpanzees, gorillas, and orangutans—the hominids 15
Subfamily Homininae Humans, chimpanzees, and gorillas (the African apes) 8
Tribe Hominini Genera Homo, Pan (chimpanzees), and the extinct Australopithecines 5.8
Subtribe Hominina Genus Homo and close human relatives and ancestors after splitting from Pan—the hominins ≥4
Genus Homo Humans 2.5
Subgenus Homo Archaic humans 0.6
Species Homo sapiens Anatomically modern humans 0.3
Subspecies Homo sapiens sapiens Extant modern humans 0.07?

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Timeline of complex evolution of humans:

55 million years ago – First primitive primates evolve

15 million years ago – Hominidae (great apes) evolve from the ancestors of the gibbon

8 million years ago – First gorillas evolve. Later, chimp and human lineages diverge

5.5 million years ago – Ardipithecus, early ‘proto-human’ shares traits with chimps and gorillas

4 million years ago – Ape like early humans, the Australopithecines appeared. They had brains no larger than a chimpanzee’s but other more human like features

3.9-2.9 million years ago – Australoipithecus afarensis lived in Africa.

2.7 million years ago – Paranthropus, lived in woods and had massive jaws for chewing

2.3 million years ago – Homo habalis first thought to have appeared in Africa

1.85 million years ago – First ‘modern’ hand emerges

1.8 million years ago – Homo ergaster begins to appear in fossil record

1.6 million years ago – Hand axes become the first major technological innovation

800,000 years ago – Early humans control fire and create hearths. Brain size increases rapidly

400,000 years ago – Neanderthals first begin to appear and spread across Europe and Asia

200,000 years ago – Homo sapiens – modern humans – appear in Africa

40,000 years ago – Modern humans reach Europe

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Dating methods:

Dating Rocks and Fossils using Geologic Methods:

A fossil can be studied to determine what kind of organism it represents, how the organism lived, and how it was preserved. However, by itself a fossil has little meaning unless it is placed within some context. The age of the fossil must be determined so it can be compared to other fossil species from the same time period. Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.  For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years. By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time. However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared.

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There are three general approaches that allow scientists to date geological materials and answer the question: “How old is this fossil?” First, the relative age of a fossil can be determined. Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event. Second, it is possible to determine the numerical age for fossils or earth materials. Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Third, magnetism in rocks can be used to estimate the age of a fossil site. This method uses the orientation of the Earth’s magnetic field, which has changed through time, to determine ages for fossils and rocks.

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Relative dating to determine the age of rocks and fossils:

Stratigraphy:

The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff. The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata.

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Geologists have established a set of principles that can be applied to sedimentary and volcanic rocks that are exposed at the Earth’s surface to determine the relative ages of geological events preserved in the rock record. For example, in the rocks exposed in the walls of the Grand Canyon, there are many horizontal layers, which are called strata. The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks. Stratigraphy is the science of deciphering the “layer-cake” that is the sedimentary record, and has been compared to a jigsaw puzzle. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil’s age must lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is very difficult to match up rock beds that are not directly next to one another. However, fossils of species that survived for a relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy. Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents.  In the Grand Canyon, the layers of strata are nearly horizontal. Most sediment is either laid down horizontally in bodies of water like the oceans, or on land on the margins of streams and rivers. Each time a new layer of sediment is deposited it is laid down horizontally on top of an older layer. This is the principle of original horizontality: layers of strata are deposited horizontally or nearly horizontally. Thus, any deformations of strata must have occurred after the rock was deposited. The principle of superposition builds on the principle of original horizontality. The principle of superposition states that in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it. Accordingly, the oldest rocks in a sequence are at the bottom and the youngest rocks are at the top. Sometimes sedimentary rocks are disturbed by events, such as fault movements, that cut across layers after the rocks were deposited. This is the principle of cross-cutting relationships. The principle states that any geologic features that cut across strata must have formed after the rocks they cut through. The principles of original horizontality, superposition, and cross-cutting relationships allow events to be ordered at a single location. However, they do not reveal the relative ages of rocks preserved in two different areas. In this case, fossils can be useful tools for understanding the relative ages of rocks. Each fossil species reflects a unique period of time in Earth’s history. The principle of faunal succession states that different fossil species always appear and disappear in the same order, and that once a fossil species goes extinct, it disappears and cannot reappear in younger rocks. [Faunal is the animals of a given region or period considered as a whole]. Fossil species that are used to distinguish one layer from another are called index fossils. Index fossils occur for a limited interval of time. Usually index fossils are fossil organisms that are common, easily identified, and found across a large area. Because they are often rare, primate fossils are not usually good index fossils. Organisms like pigs and rodents are more typically used because they are more common, widely distributed, and evolve relatively rapidly.  Using the principle of faunal succession, if an unidentified fossil is found in the same rock layer as an index fossil, the two species must have existed during the same period of time. If the same index fossil is found in different areas, the strata in each area were likely deposited at the same time. Thus, the principle of faunal succession makes it possible to determine the relative age of unknown fossils and correlate fossil sites across large discontinuous areas.

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Determining the numerical age of rocks and fossils:

Unlike relative dating methods, absolute dating methods provide chronological estimates of the age of certain geological materials associated with fossils, and even direct age measurements of the fossil material itself. To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events. Potassium-argon dating, Argon-argon dating, Carbon-14 (or Radiocarbon), and Uranium series. All of these methods measure the amount of radioactive decay of chemical elements; the decay occurs in a consistent manner, like a clock, over long periods of time. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better.  Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers.  Geologists also use other methods – such as electron spin resonance and thermoluminescence, which assess the effects of radioactivity on the accumulation of electrons in imperfections, or “traps,” in the crystal structure of a mineral – to determine the age of the rocks or fossils.

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Radiometric dating:

All elements contain protons and neutrons, located in the atomic nucleus, and electrons that orbit around the nucleus. In each element, the number of protons is constant while the number of neutrons and electrons can vary. Atoms of the same element but with different number of neutrons are called isotopes of that element. Each isotope is identified by its atomic mass, which is the number of protons plus neutrons. For example, the element carbon has six protons, but can have six, seven, or eight neutrons. Thus, carbon has three isotopes: carbon 12 (12C), carbon 13 (13C), and carbon 14 (14C) (see figure below).

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Figure shows Radioactive isotopes and how they decay through time.

(a) Carbon has three isotopes with different numbers of neutrons: carbon 12 (C12, 6 protons + 6 neutrons), carbon 13 (C13, 6 protons + 7 neutrons), and carbon 14 (C14, 6 protons + 8 neutrons). C12 and C13 are stable. The atomic nucleus in C14 is unstable making the isotope radioactive. Because it is unstable, occasionally C14 undergoes radioactive decay to become stable nitrogen (N14). (b) The radioactive atoms (parent isotopes) in any mineral decay over time into stable daughter isotopes. The amount of time it takes for half of the parent isotopes to decay into daughter isotopes is known as the half-life of the radioactive isotope. When the quantities of the parent and daughter isotopes are equal, one half-life has occurred. If the half-life of an isotope is known, the abundance of the parent and daughter isotopes can be measured and the amount of time that has elapsed since the “radiometric clock” started can be calculated.  For example, if the measured abundance of 14C and 14N in a bone are equal, one half-life has passed and the bone is 5,730 years old (an amount equal to the half-life of 14C). If there is three times less 14C than 14N in the bone, two half-lives have passed and the sample is 11,460 years old. However, if the bone is 70,000 years or older the amount of 14C left in the bone will be too small to measure accurately. Thus, radiocarbon dating is only useful for measuring things that were formed in the relatively recent geologic past. Luckily, there are methods, such as the commonly used potassium-argon (K-Ar) method, that allows dating of materials that are beyond the limit of radiocarbon dating (Table below).

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Most isotopes found on Earth are generally stable and do not change. However some isotopes, like 14C, have an unstable nucleus and are radioactive. This means that occasionally the unstable isotope will change its number of protons, neutrons, or both. This change is called radioactive decay. For example, unstable 14C transforms to stable nitrogen (14N). The atomic nucleus that decays is called the parent isotope. The product of the decay is called the daughter isotope. In the above example, 14C is the parent and 14N is the daughter.  Some minerals in rocks and organic matter (e.g., wood, bones, and shells) can contain radioactive isotopes. The abundances of parent and daughter isotopes in a sample can be measured and used to determine their age. This method is known as radiometric dating. Some commonly used dating methods are summarized in Table below. The rate of decay for many radioactive isotopes has been measured and does not change over time. Thus, each radioactive isotope has been decaying at the same rate since it was formed, ticking along regularly like a clock. For example, when potassium is incorporated into a mineral that forms when lava cools, there is no argon from previous decay (argon, a gas, escapes into the atmosphere while the lava is still molten). When that mineral forms and the rock cools enough that argon can no longer escape, the “radiometric clock” starts. Over time, the radioactive isotope of potassium decays slowly into stable argon, which accumulates in the mineral.

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Comparison of commonly used dating methods:

Name of Method Age Range of Application Material Dated Methodology
Radiocarbon 1 – 70,000 years Organic material such as bones, wood, charcoal, shells Radioactive decay of 14C in organic matter after removal from bioshpere
K-Ar dating 1,000 – billion of years Potassium-bearing minerals and glasses Radioactive decay of 40K in rocks and minerals
Uranium-Lead 10,000 – billion of years Uranium-bearing minerals Radioactive decay of uranium to lead via two separate decay chains
Uranium series 1,000 – 500,000 years Uranium-bearing minerals, corals, shells, teeth, CaCO3 Radioactive decay of 234U to 230Th
Fission track 1,000 – billion of years Uranium-bearing minerals and glasses Measurement of damage tracks in glass and minerals from the radioactive decay of 238U
Luminescence (optically or thermally stimulated) 1,000 – 1,000,000 years Quartz, feldspar, stone tools, pottery Burial or heating age based on the accumulation of radiation-induced damage to electron sitting in mineral lattices
Electron Spin Resonance (ESR) 1,000 – 3,000,000 years Uranium-bearing materials in which uranium has been absorbed from outside sources Burial age based on abundance of radiation-induced paramagnetic centers in mineral lattices
Cosmogenic Nuclides 1,000 – 5,000,000 years Typically quartz or olivine from volcanic or sedimentary rocks Radioactive decay of cosmic-ray generated nuclides in surficial environments
Magnetostratigraphy 20,000 – billion of years Sedimentary and volcanic rocks Measurement of ancient polarity of the earth’s magnetic field recorded in a stratigraphic succession
Tephrochronology 100 – billions of years Volcanic ejecta Uses chemistry and age of volcanic deposits to establish links between distant stratigraphic successions

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Radiation, which is a byproduct of radioactive decay, causes electrons to dislodge from their normal position in atoms and become trapped in imperfections in the crystal structure of the material. Dating methods like thermoluminescence, optical stimulating luminescence and electron spin resonance, measure the accumulation of electrons in these imperfections, or “traps,” in the crystal structure of the material. If the amount of radiation to which an object is exposed remains constant, the amount of electrons trapped in the imperfections in the crystal structure of the material will be proportional to the age of the material. These methods are applicable to materials that are up to about 100,000 years old. However, once rocks or fossils become much older than that, all of the “traps” in the crystal structures become full and no more electrons can accumulate, even if they are dislodged.

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Using paleomagnetism to date rocks and fossils:

Paleomagnetism measures the ancient orientation of the Earth’s magnetic field to help determine the age of rocks. The Earth is like a gigantic magnet. It has a magnetic north and south pole and its magnetic field is everywhere. Just as the magnetic needle in a compass will point toward magnetic north, small magnetic minerals that occur naturally in rocks point toward magnetic north, approximately parallel to the Earth’s magnetic field. Because of this, magnetic minerals in rocks are excellent recorders of the orientation, or polarity, of the Earth’s magnetic field.

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The earth’s magnetic field can be measured to determine the polarity of a rock sample.

(a) The earth is surrounded by a magnetic field generated by the magnetism in the core of the earth. Small magnetic grains in rocks will orient themselves to be parallel to the direction of the magnetic field pointing towards the North Pole. (b) The geomagnetic polarity time scale shows how the polarity of the earth’s magnetic field has changed through time. Black bands indicate times of normal polarity and white bands indicate times of reversed polarity.

Through geologic time, the polarity of the Earth’s magnetic field has switched, causing reversals in polarity. The Earth’s magnetic field is generated by electrical currents that are produced by convection in the Earth’s core. During magnetic reversals, there are probably changes in convection in the Earth’s core leading to changes in the magnetic field. The Earth’s magnetic field has reversed many times during its history. When the magnetic north pole is close to the geographic north pole (as it is today), it is called normal polarity. Reversed polarity is when the magnetic “north” is near the geographic South Pole. Using radiometric dates and measurements of the ancient magnetic polarity in volcanic and sedimentary rocks (termed paleomagnetism), geologists have been able to determine precisely when magnetic reversals occurred in the past. Combined observations of this type have led to the development of the geomagnetic polarity time scale (GPTS) (see figure above). The GPTS is divided into periods of normal polarity and reversed polarity.  Geologists can measure the paleomagnetism of rocks at a site to reveal its record of ancient magnetic reversals. Every reversal looks the same in the rock record, so other lines of evidence are needed to correlate the site to the GPTS. Information such as index fossils or radiometric dates can be used to correlate a particular paleomagnetic reversal to a known reversal in the GPTS. Once one reversal has been related to the GPTS, the numerical age of the entire sequence can be determined.

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Here of some of the well-tested methods of dating used in the study of early humans:

  1. Biochronology. Since animal species change over time, the fauna can be arranged from younger to older. At some sites, animal fossils can be dated precisely by one of these other methods. For sites that cannot be readily dated, the animal species found there can be compared to well-dated species from other sites. In this way, sites that do not have radioactive or other materials for dating can be given a reliable age estimate.
  2. Family-tree relationships may also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated “family tree” says A was an ancestor of B and C, then A must have evolved more than X million years ago.
  3. Molecular genetic clock [vide infra]. This method compares the amount of genetic difference between living organisms and computes an age based on well-tested rates of genetic mutation over time. It is possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at a constant rate. These “molecular clocks”, however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Since genetic material (like DNA) decays rapidly, the molecular clock method can’t date very old fossils. It’s mainly useful for figuring out how long ago living species or populations shared a common ancestor, based on their DNA.

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Effective ranges of major dating methods relevant to human evolution studies:

 

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Fossils:

When organisms die, they often decompose rapidly or are consumed by scavengers, leaving no permanent evidences of their existence. However, occasionally, some organisms are preserved. The remains or traces of organisms from a past geologic age embedded in rocks by natural processes are called fossils. They are extremely important for understanding the evolutionary history of life on Earth, as they provide direct evidence of evolution and detailed information on the ancestry of organisms. Paleontology is the study of past life based on fossil records and their relations to different geologic time periods.

Fossil is:

(1) Any preserved evidence of life from a past geological age, such as the impressions and remains of organisms embedded in stratified rocks.

(2) The mineralized remains of an animal or plant.

They form by a process called fossilization. Fossils are usually found in rock, but they can also be found in mud or gravel. Most fossils are found when the rocks of the landscape are worn away by wind and water, exposing the fossils. In China, dinosaur fossils were once thought to be dragon bones.

Fossils include shells, imprints, burrows, coprolites and organically-produced chemicals. The oldest fossils were bacteria that existed 3.8 billion years old. Harder tissues, such as bones and teeth become preserved as fossils more often than softer tissues. This is because softer tissues such as skin and flesh, are more likely to be eaten by animals or decay before they can be preserved. Fossils are once thought of to be all from extinct species until some were found to belong to species that are still living.

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Hoplopteryx: Fish fossil:

The skeleton of this fish was well preserved by fossilization. The scales, fins, and the shape of the mouth can clearly be seen. The large eye sockets reveal that the fish had big eyes and good vision for finding and catching its prey. Hoplopteryx is an extinct relative of modern fish known as slimeheads. This fossil was discovered in a layer of chalk rock in southern England. Hoplopteryx lived in the late Cretaceous Period, probably in shallow seas.

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What is a fossil? Generally, we think of bones, shells, or teeth that are buried in rock, but fossils can also be outlines of leaves or footprints or trails. This second set of fossils, which are the outlines of items from the past rather than the items themselves, are called trace fossils. Fossils are formed when sediment covers some material, such as a piece of bone. Very gradually, the bone becomes impregnated with chemicals from the surrounding rock. Eventually all that remains is essentially a piece of rock in the shape of the original bone, or material. Taken together, fossils can be used to construct a fossil record, which is a timeline of fossils reaching back through history. Several factors must be taken into account when constructing such a record. The strata of rock in which fossils are found give us clues about their relative ages. Similarly, new technological techniques such as radioactive carbon dating help determine the absolute ages of fossils. In addition to supplying a fossil’s relative age, rock strata can also give clues about the environments in which an animal or plant lived. The chemical make-up of these strata can tell us the balance of gases in ancient atmospheres. Major cataclysmic events such as eruptions and meteor strikes also leave there mark on the fossil record.

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There are, however, limitations on the information fossils can supply. Fossilization is an improbable event. Most often, bones and other materials are crushed or consumed before they can be fossilized. In addition, fossils can only form in areas where sedimentary rock is formed, such as ocean floors. Organisms that live in these environments are therefore more likely to be fossilized. Erosion of exposed rock faces or through the crushing action of geological movements can destroy fossils even after they are formed. All of these condition lead to large and numerous gaps in the fossil record.

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Our ancestral fossil record:

More than 2000 ancient individuals are now found in our ancestral fossil record. Some of these individuals are represented by reasonably complete fossil skeletons. However, this is relatively rare, particularly for our older ancestors who lived millions of years ago. Generally, individuals who lived more recently tend to have more complete fossil skeletons than those who lived longer ago. Often only a handful of fossil bones or bone fragments are found and sometimes all that remains of a particular individual is a single tooth!

Jaws and teeth: Jaws and teeth are the most commonly found fossils. These are especially hard parts of the skeleton and therefore have a better chance of lasting long enough to become fossilised. The numbers, types and shapes of the teeth tell us much about the diets, lifestyles and relationships of their owners. They can even help indicate an individual’s age at the time of death.

Skulls: Skulls can provide details about the size and shape of the brain, face and teeth. The base of the skull can also provide information on posture as it shows how the head was supported on the body.

Figure above shows anatomical comparison of the skulls of a modern human (left) and Homo neanderthalensis (right).

Limb bones: Bone fossils can provide information about some of the soft body tissues that did not become fossilised. Surface markings left on the bones show where muscles, tendons and ligaments used to attach and where blood vessels and nerves used to lie. They can also provide information about how tall and how heavy the individual would have been. The limbs can also tell us how their owners moved about.

Brains: Sand and mud can fill a fossil skull and then harden to produce natural fossil endocasts of the brain cavity. This preserves the size, shape and surface features showing different regions of the brain, blood vessels and brain folds.

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Finding ancestors’ fossils:

Most of our ancestors’ fossils are found in sites that were once on the margins of ancient lakes and rivers, inside caves or were subject to volcanic eruptions. In some sites, the conditions needed for fossilisation occurred over relatively short time spans. In others, a rich fossil record accumulated over millions of years. Fossils of our earliest ancestors have only been found in Africa, especially in the Rift Valleys of East Africa and in limestone caves in South Africa. On other continents, our ancestors’ fossils are mostly less than about one million years old. They are especially found in caves in the Middle East, southern Europe, and parts of Asia, including India, China and Indonesia. Remains (often unfossilised) younger than about 40,000 years old are found in Europe, Australia, Flores in Indonesia, and the Americas.

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What does the fossil record show?

Fossils provide a unique view into the history of life by showing the forms and features of life in the past.  Fossils tell us how species have changed across long periods of the Earth’s history.  For instance, in 1998, scientists found a fossil showing an animal at the transition from sea creature to land creature. This tetrapod had a hand-like fin, confirming a prediction of evolutionary biology. Though the fossil record does not include every plant and animal that ever lived, it provides substantial evidence for the common descent of life via evolution. The fossil record is a remarkable gift for the study of nature.

Evidence of Gradual Change:

Organisms have changed significantly over time. In rocks more than 1 billion years old, only fossils of single-celled organisms are found. Moving to rocks that are about 550 million years old, fossils of simple, multicellular animals can be found. At 500 million years ago, ancient fish without jawbones surface; and at 400 million years ago, fish with jaws are found. Gradually, new animals appear: amphibians at 350 million years ago, reptiles at 300 million years ago, mammals at 230 million years ago, and birds at 150 million years ago. As the rocks become more and more recent, the fossils look increasingly like the animals we observe today.

Transitional Forms: Few and Far Between:

Transitional forms occur just when one might expect to see a change from one body type to another. However, a common objection is that few transitional fossils have been discovered; thus many lineages cannot be traced smoothly. There are several reason for these gaps in the fossil record. First, fossilization is a very rare event. Plus, transitional species tend to appear in small populations, where rapid changes in the environment can provide a stronger evolutionary drive. Finally, because fossilization itself is a rare event, smaller populations are sure to produce fewer fossils. The fact that transitional species have been found at all is remarkable, and it offers further support of gradual, evolutionary change.

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First fossils:

A major problem in the 19th century was the lack of fossil intermediaries. Neanderthal remains were discovered in a limestone quarry in 1856, three years before the publication of On the Origin of Species, and Neanderthal fossils had been discovered in Gibraltar even earlier, but it was originally claimed that these were human remains of a creature suffering some kind of illness.

Despite the 1891 discovery by Eugène Dubois of what is now called Homo erectus at Trinil, Java, it was only in the 1920s when such fossils were discovered in Africa, that intermediate species began to accumulate. In 1925, Raymond Dart described Australopithecus africanus. The type specimen was the Taung Child, an australopithecine infant which was discovered in a cave. The child’s remains were a remarkably well-preserved tiny skull and an endocast of the brain. Although the brain was small (410 cubic-cm), its shape was rounded, unlike that of chimpanzees and gorillas, and more like a modern human brain. Also, the specimen showed short canine teeth, and the position of the foramen magnum (the hole in the skull where the spine enters) was evidence of bipedal locomotion. All of these traits convinced Dart that the Taung Child was a bipedal human ancestor, a transitional form between apes and humans.

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The East African fossils—and Homo naledi in South Africa:

During the 1960s and 1970s, hundreds of fossils were found in East Africa in the regions of the Olduvai Gorge and Lake Turkana. The driving force of these searches was the Leakey family, with Louis Leakey and his wife Mary Leakey, and later their son Richard and daughter-in-law Meave—all successful and world-renowned fossil hunters and paleoanthropologists. From the fossil beds of Olduvai and Lake Turkana they amassed specimens of the early hominins: the australopithecines and Homo species, and even Homo erectus. These finds cemented Africa as the cradle of humankind. In the late 1970s and the 1980s, Ethiopia emerged as the new hot spot of paleoanthropology after “Lucy”, the most complete fossil member of the species Australopithecus afarensis, was found in 1974 by Donald Johanson near Hadar in the desertic Afar Triangle region of northern Ethiopia. Although the specimen had a small brain, the pelvis and leg bones were almost identical in function to those of modern humans, showing with certainty that these hominins had walked erect.  Lucy was classified as a new species, Australopithecus afarensis, which is thought to be more closely related to the genus Homo as a direct ancestor, or as a close relative of an unknown ancestor, than any other known hominid or hominin from this early time range; The specimen was nicknamed “Lucy” after the Beatles’ song “Lucy in the Sky with Diamonds”, which was played loudly and repeatedly in the camp during the excavations. The Afar Triangle area would later yield discovery of many more hominin fossils, particularly those uncovered or described by teams headed by Tim D. White in the 1990s, including Ardipithecus ramidus and Ardipithecus kadabba. In 2013, fossil skeletons of Homo naledi, an extinct species of hominin assigned (provisionally) to the genus Homo, were found in the Rising Star Cave system, a site in South Africa’s Cradle of Humankind region in Gauteng province near Johannesburg.  In September 2015, fossils of at least fifteen individuals, amounting to 1550 specimens, have been excavated from the cave. The species is characterized by a body mass and stature similar to small-bodied human populations, a smaller endocranial volume similar to Australopithecus, and a cranial morphology (skull shape) similar to early Homo species. The skeletal anatomy combines primitive features known from australopithecines with features known from early hominins. The individuals show signs of having been deliberately disposed of within the cave near the time of death.

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The quest for the earliest hominin:

In the 1990s, several teams of paleoanthropologists were working throughout Africa looking for evidence of the earliest divergence of the hominin lineage from the great apes. In 1994, Meave Leakey discovered Australopithecus anamensis. The find was overshadowed by Tim D. White’s 1995 discovery of Ardipithecus ramidus, which pushed back the fossil record to 4.2 million years ago. In 2000, Martin Pickford and Brigitte Senut discovered, in the Tugen Hills of Kenya, a 6-million-year-old bipedal hominin which they named Orrorin tugenensis. And in 2001, a team led by Michel Brunet discovered the skull of Sahelanthropus tchadensis which was dated as 7.2 million years ago, and which Brunet argued was a bipedal, and therefore a hominid—that is, a hominin.

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Early Homo sapiens:

Anatomically modern humans originated in Africa about 250,000 years ago. The trend in cranial expansion and the acheulean elaboration of stone tool technologies which occurred between 400,000 years ago and the second interglacial period in the Middle Pleistocene (around 250,000 years ago) provide evidence for a transition from H. erectus to H. sapiens. In the Recent African Origin (RAO) scenario, migration within and out of Africa eventually replaced the earlier dispersed H. erectus. Homo sapiens idaltu, found at site Middle Awash in Ethiopia, lived about 160,000 years ago. It is the oldest known anatomically modern human and classified as an extinct subspecies. Fossils of early Homo sapiens were found in Qafzeh cave in Israel and have been dated to 80,000 to 100,000 years ago. However these humans seem to have either become extinct or retreated back to Africa 70,000 to 80,000 years ago, possibly replaced by south bound Neanderthals escaping the colder regions of ice age Europe. Hua Liu & al. analyzing autosomal microsatellite markers dates to 56,000±5,700 years ago mtDNA evidence. He interprets the paleontological fossil of early modern human from Qafzeh cave as an isolated early offshoot that retracted back to Africa.  All other fossils of fully modern humans outside Africa have been dated to more recent times. The oldest well dated fossils found outside Africa are from Lake Mungo, Australia, and have been dated to about 42,000 years ago. The Tianyuan cave remains in Liujiang region China have a probable date range between 38,000 and 42,000 years ago. They are most similar in morphology to Minatogawa Man, modern humans dated between 17,000 and 19,000 years ago and found on Okinawa Island, Japan. However, others have dated Liujang Man to 111,000 to 139,000 years before the present. Beginning about 100,000 years ago evidence of more sophisticated technology and artwork begins to emerge and by 50,000 years ago fully modern behaviour becomes more prominent. Stone tools show regular patterns that are reproduced or duplicated with more precision while tools made of bone and antler appear for the first time.

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Bone paleohistology and human evolution:

Bone Paleohistology is the study of the microstructure of mineralized bone tissue of fossil skeleton. Life-history and biological evolution of hominins may be studied through the analysis of their mineralised tissues. Bones grow changing in size and shape, and perform structural and reservoir functions in respond to a variety of stimuli, which influence the bone cellular mechanism responsible of the growth of bone tissue. Structure and the osteological variables of the bone tissue provides a great source of information about aspects of hominin evolution such as growth processes, estimation of age at death, diet, pathologies, and biomechanics. In this sense, bone paleohistology, or the study of the structure of fossil bone tissue, is a powerful tool that may provide key information on the evolution and biological aspects of the fossil human populations.

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DNA study and sequencing:

There are many ways of tracking the progress of evolution in the past and observing the changes it causes in the present, but the study of genetics allows biologists to pinpoint specific mutations and modifications that have resulted in evolutionary change. When Charles Darwin first conceived of the theory of evolution by natural selection, he knew that some mechanism for heredity must exist, but he could not explain what it was or how it worked. The modern study of genetics has given us the last piece of the puzzle, allowing us to understand mutation and inheritance, and providing us with both the explanation of, and the evidence for, evolution as we now define it: the change in frequencies of gene variations over time.

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The Universal Genetic Code:

The DNA in living things is highly conserved. DNA has only four nitrogenous bases that code for all differences in living things on Earth. Adenine, Cytosine, Guanine, and Thymine line up in a specific order and a group of three, or a codon, code for one of 20 amino acids found on Earth. The order of those amino acids determines what protein is made. Remarkably enough, only four nitrogenous bases that make only 20 amino acids account for all diversity of life on Earth. There has not been any other code or system found in any living, or once living, organism on Earth. Organisms from bacteria to humans to dinosaurs all have the same DNA system as a genetic code. This may point to evidence that all life evolved from a single common ancestor.

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Changes in DNA:

All cells are pretty well-equipped with a way to check a DNA sequence for mistakes before and after cell division, or mitosis. Most mutations, or changes in DNA, are caught before copies are made and those cells are destroyed. However, there are times when small changes do not make that much of a difference and will pass through the checkpoints. These mutations may add up over time and change some of the functions of that organism. If these mutations happen in somatic cells, in other words, normal adult body cells, then these changes do not affect future offspring. If the mutations happen in gametes, or sex cells, those mutations do get passed down to the next generation and may affect the function of the offspring. These gamete mutations lead to microevolution.

Recently Chinese Scientist showed that the mutation of DNA would drive human evolution. To be more specific, transposons, a class of DNA elements, can jump from one position to another in a genome, and cause DNA mutations. Transponsons are active in early embryos, and the mutations caused by their mobility are more likely to be passed to the germ line, and then to the next generations, scientists added.

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Evidence for Evolution in DNA:

DNA has only come to be understood over the last century. The technology has been improving and has allowed scientists to not only map out entire genomes of many species, but they also use computers to compare those maps. By entering genetic information of different species, it is easy to see where they overlap and where there are differences. The more closely species are related on the phylogenetic tree of life, the more closely their DNA sequences will overlap. Even very distantly related species will have some degree of DNA sequence overlap. Certain proteins are needed for even the most basic processes of life, so those selected parts of the sequence that codes for those proteins will be conserved in all species on Earth. Now that DNA fingerprinting has become easier, cost effective, and efficient, the DNA sequences of a wide variety of species can be compared. In fact, it is possible to estimate when the two species diverged or branched off through speciation. The larger the percentage of differences in the DNA between two species, the greater the amount of time the two species have been separate. These “molecular clocks” can be used to help fill in the gaps of the fossil record. Even if there are missing links within the timeline of history on Earth, the DNA evidence can give clues as to what happened during those time periods. While random mutation events may throw off the molecular clock data at some points, it is still a pretty accurate measure of when species diverged and became new species.

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Comparison of DNA sequences allows organisms to be grouped by sequence similarity, and the resulting phylogenetic trees are typically congruent with traditional taxonomy, and are often used to strengthen or correct taxonomic classifications. Sequence comparison is considered a measure robust enough to correct erroneous assumptions in the phylogenetic tree in instances where other evidence is scarce. For example, neutral human DNA sequences are approximately 1.2% divergent (based on substitutions) from those of their nearest genetic relative, the chimpanzee, 1.6% from gorillas, and 6.6% from baboons. Genetic sequence evidence thus allows inference and quantification of genetic relatedness between humans and other apes. The sequence of the 16S ribosomal RNA gene, a vital gene encoding a part of the ribosome, was used to find the broad phylogenetic relationships between all extant life. The analysis, originally done by Carl Woese, resulted in the three-domain system, arguing for two major splits in the early evolution of life. The first split led to modern Bacteria and the subsequent split led to modern Archaea and Eukaryotes.

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Some DNA sequences are shared by very different organisms. It has been predicted by the theory of evolution that the differences in such DNA sequences between two organisms should roughly resemble both the biological difference between them according to their anatomy and the time that had passed since these two organisms have separated in the course of evolution, as seen in fossil evidence. The rate of accumulating such changes should be low for some sequences, namely those that code for critical RNA or proteins, and high for others that code for less critical RNA or proteins; but for every specific sequence, the rate of change should be roughly constant over time. These results have been experimentally confirmed. Two examples are DNA sequences coding for rRNA, which is highly conserved, and DNA sequences coding for fibrinopeptides (amino acid chains that are discarded during the formation of fibrin), which are highly non-conserved.

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Mutation rate:

The haploid human genome has about 3 billion nucleotide sites and, over time, genes at certain sites mutate. If a parent passes down that mutation to their children, who pass it to further generations, that mutation acts as a ‘family seal’ stamped onto the DNA. Scientists use these mutations to piece together evolutionary history hundreds of thousands of years in the past. By searching for shared gene mutations along the nucleotide sites of various human populations, scientists can estimate when groups diverged and the sizes of populations contributing to the gene pool. For the last 15 years or so, molecular anthropologists have been comparing the DNA of living humans of diverse origins to build evolutionary trees. Mutations occur in our DNA at a regular rate and will often be passed along to our children. It is these differences (polymorphisms) that, on a genotypic level, make us all unique and analysis of these differences will show how closely we are related. [Vide infra DNA dating].

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ERV:

When geneticists examine the genomes of species believed to share a recent common ancestry, this is exactly what they observe. Endogenous retroviruses (ERVs) are a particularly conclusive example of shared genetic ancestry. ERVs are the result of a virus infecting an organism and inserting portions of viral genetic material into the DNA of the organism’s reproductive cells; the modified DNA containing the viral mutation is then passed on to the offspring of the infected specimen. The retroviral DNA sequence does not code for anything, and so that particular sequence is highly unlikely to appear spontaneously.  If a given ERV gene sequence appears at the same place in the genomes of two different species, it strongly suggests a common ancestry for those two species, because that is the simplest way to explain that particular sequence of non-coding DNA appearing at that precise point in the genomes of multiple species. In practice, this phenomenon is observed thousands of times over in the human genome; there are approximately 200 thousand ERV sequences in the human genome, and less than one hundred of those are not shared by the species most closely related to humans, the chimpanzee.

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Chromosome 2:

Human evolution and common ancestry with other species is the facet of evolutionary biology held to be most controversial by the lay populace, but a closer look at human chromosomes reveals still further evidence for evolution from a shared ancestor with other primates. Humans have 23 pairs of chromosomes, while other great apes, such as chimpanzees, gorillas, and orangutans, possess 24 pairs. All members of Hominidae except humans, Neanderthals, and Denisovans have 24 pairs of chromosomes. Human chromosome 2 is a result of an end-to-end fusion of two ancestral chromosomes.

The evidence for this includes:

  1. The correspondence of chromosome 2 to two ape chromosomes. The closest human relative, the chimpanzee, has near-identical DNA sequences to human chromosome 2, but they are found in two separate chromosomes. The same is true of the more distant gorilla and orangutan.
  2. The presence of a vestigial centromere. Normally a chromosome has just one centromere, but in chromosome 2 there are remnants of a second centromere in the q21.3–q22.1 region.
  3. The presence of vestigial telomeres. These are normally found only at the ends of a chromosome, but in chromosome 2 there are additional telomere sequences in the q13 band, far from either end of the chromosome.

According to researcher J. W. IJdo, “We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2.”

However Dr. Tomkins’s research gets interesting: He finds that the place on chromosome 2 where the two chromosomes are supposed to have fused is right in the intron of a gene! The gene is charmingly named DDX11L2, and it is known to be used in several different cells, including those performing tasks related to the nervous system, muscle system, immune system, and reproductive system. It’s really hard to understand how two chromosomes could fuse at the intron of a functional gene, but that’s not the end of the story. The fusion site also contains an important sequence of DNA called a transcription factor binding site. This is a sequence to which a molecule can attach so as to regulate how often the gene is used. So not only is the fusion site right in the middle of a functional gene, it is actually found in a region that helps to regulate how that gene is expressed. That makes it even more difficult to understand how a fusion event could have taken place there. Is this conclusive evidence against the idea that our second chromosome is the result of two independent chromosomes being fused together?

Not really. After all, the spot that Dr. Tomkins studied does bear a remarkable resemblance to the kinds of sequences found when two chromosomes fuse together. Thus, if it is not the result of chromosome fusion, we need to understand why that region of the chromosome has a sequence characteristic of such things. Also, it is well known that the human chromosome 2 has two centromeres, and typical chromosomes have only one and a fusion event would explain why this chromosome has two centromeres.

Human Chromosome 2 is a fusion of two ancestral chromosomes.  All great apes apart from man have 24 pairs of chromosomes. There is therefore a hypothesis that the common ancestor of all great apes had 24 pairs of chromosomes and that the fusion of two of the ancestor’s chromosomes created chromosome 2 in humans. The evidence for this hypothesis is very strong. The study of the human genome allows biologists to trace the genetic development of the human species, and reveals strong similarities to the evolutionary cousins of humans while showing how those genes have changed since the two species diverged.

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Pseudogenes:

Further evidence for common descent comes from genetic detritus such as pseudogenes, regions of DNA that are orthologous to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration. Such genes are called “fossil” genes. Pseudogenes are remnants of genes that no longer function but continue to be carried along in DNA as excess baggage. Pseudogenes also change through time, as they are passed on from ancestors to descendants, and they offer an especially useful way of reconstructing evolutionary relationships. Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparing the biochemistry and genetics of existing organisms.  With functioning genes, one possible explanation for the relative similarity between genes from different organisms is that their ways of life are similar—for example, the genes from a horse and a zebra could be more similar because of their similar habitats and behaviors than the genes from a horse and a tiger. But this possible explanation does not work for pseudogenes, since they perform no function. Rather, the degree of similarity between pseudogenes must simply reflect their evolutionary relatedness. The more remote the last common ancestor of two organisms, the more dissimilar their pseudogenes will be.

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Microsatellites:

Because all humans have virtually identical DNA, geneticists look for subtle differences between populations.  One method involves looking at so-called microsatellites – short, repetitive segments of DNA that differ between populations.  These microsatellites have a high mutation, or error, rate as they are passed from generation to generation, making them a useful tool to study when two populations diverged.  Researchers from Stanford University, US, and the Russian Academy of Sciences compared 377 microsatellite markers in DNA collected from 52 regions around the world.  Analysis revealed a close genetic kinship between two hunter-gatherer populations in sub-Saharan Africa – the Mbuti pygmies of the Congo Basin and the Khosian bushmen of Botswana.

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Challenges in extracting Ancient DNA:

Working with ancient DNA can be challenging. It can be difficult to find sufficient material to work with after decomposition and fossilization have occurred and to eliminating contamination from modern human DNA. Distinguishing between modern human and ancient genetic material is particularly difficult when the ancient DNA comes from our close relatives. Organisms decompose after death. Water, oxygen and microbes break down DNA, which is a very fragile molecule. Therefore ancient DNA tends to be found in small quantities and is generally fragmentary and damaged. Still, it is sometimes possible to amplify the recovered DNA and obtain a viable sample for analysis. One key factor in harvesting ancient DNA is having technology that allows for the smallest of DNA samples to be detected and collected for study. Contamination by modern DNA is a particularly difficult problem to solve. Many fossils have been handled by researchers for years and could be contaminated with DNA from hundreds of sources, especially since fossil excavation and subsequent handling does not often require gloves and wearing gloves can actually impede many non-DNA related aspects of fossil study. Contamination is difficult to detect because Neanderthals and humans share much of their genetic material, making some DNA sequences indistinguishable between the two species. Researchers have developed ways to analyze the results of ancient DNA sequencing efforts to determine whether contamination is likely and how much has occurred. Analysis of the results and efforts to keep labs and specimens free of modern DNA is very important as some researchers believe that the early studies of Neanderthal DNA included modern contaminants.

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After death, DNA starts degrading immediately. It is thought that under the most favorable conditions, some DNA fragments can survive for as long as 50,000 to 100,000 years. The Feldhofer Neandertal fossil, thought to be between 30,000 and 100,000 years old, was therefore pushing the limits for this kind of work. The oldest DNA sample ever recovered to date is 700,000 years old and was recovered from an ancient horse (Millar and Lambert 2013). The oldest hominin whose DNA has been successfully sampled is a 400,000 year old Neanderthal (Meyer et al 2016). In both of these cases, and in many other cases of extraordinary DNA preservation, the DNA was recovered from fossils in extremely cold regions of the world. The ideal preservation condition for DNA is a cold and dry space with very little temperature fluctuation. Even in these circumstances, it takes a fair amount of luck in addition to extremely precise sampling technologies to retrieve DNA this old. In a study led by Viviane Slon of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and published in the journal Science on May 12, 2017, a team of evolutionary geneticists found lots of ancient DNA from mammals in sediments from caves in Europe and Asia. They found fragments of mitochondrial DNA from twelve different families of mammals in the sediments, including DNA from extinct animals like woolly mammoths, woolly rhinos, cave hyenas, and cave bears. Most exciting was the discovery of ancient human DNA in nine of those 85 samples from four of the sites: eight had Neanderthal DNA, and one had Denisovan DNA.

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Mitochondrial DNA (mtDNA):

Mitochondrial DNA is the small circular chromosome found inside mitochondria. DNA (deoxyribonucleic acid) is the gigantic molecule which is used to encode genetic information for all life on Earth. DNA molecules consist of a long strand of base molecules arranged in the form of a double helix. The bases are adenine, guanine, cytosine, and thymine, often abbreviated as A, G, C, and T. What we ordinarily think of as “our” DNA, because it controls most aspects of our physical appearance, is also known as “nuclear DNA”, because every cell in our bodies contains two copies of it in the cell nucleus. Mitochondria are small energy-producing organelles found in cells. Surprisingly, mitochondria have their own DNA molecules, entirely separate from our nuclear DNA. Most cells contain between 500 and 1000 copies of the mtDNA molecule, which makes it a lot easier to find and extract than nuclear DNA. In humans the mtDNA genome consists of about 16,000 base pairs (far shorter than our nuclear DNA), and has been completely sequenced. What makes mtDNA particularly interesting is that, unlike nuclear DNA which is equally inherited from both father and mother, mtDNA is inherited only from the mother, because all our mitochondria are descended from those in our mother’s egg cell (there may be rare exceptions to this rule, however).

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Initially, it was thought that for humans, most of the sperm remained outside of the egg. Only the head with the nuclear DNA and the centrosome, were thought to enter the egg. But that view has changed. Now it has been determined that the whole sperm enters the egg. However, virtually all of the sperm is broken down by enzymes. Only the chromosomes found in the head of the sperm in crystalline form are preserved and used in the recombination process to produce the final version of the new egg cell DNA. The typical mammalian sperm midpiece contains approximately 50–75 mitochondria with one copy of mtDNA in each. This represents an 8- to 10-fold decline in copy number during spermiogenesis. In contrast, the mammalian oocyte contains around 100,000 to 100,000,000 mitochondria, and the human oocyte in particular is estimated to contain 100,000 copies of mtDNA. Thus the oocyte’s mtDNA copy number exceeds that of the sperm by a factor of at least 1000. As the sperm takes several weeks to form and mature within the male tract before ejaculation and the mtDNA may well be degraded during this period, the simplest explanation for so called maternal inheritance is that the paternal contribution is diluted beyond the limits of detection using conventional restriction enzyme analysis. Also, the remaining sperm mitochondria and its DNA are broken down by enzymes made for that purpose. So mitochondria and its DNA from the sperm are not used. Only the mitochondria from the egg are used for the newly developing person. So, our mitochondrial DNA is essentially identical to that of our mother. Mitochondrial DNA is transferred from mother to daughter, generation after generation. The mitochondrial DNA in the son, which he got from his mother, is a dead end street, since his mitochondrial DNA will not be used in his children. Nuclear DNA changes a lot since it undergoes recombination in every generation. However, the mitochondrial DNA gets transferred from generation to generation without any recombination. Only the normal mutation rate that occurs when DNA is replicated allows the mitochondrial DNA to change. Several unique properties of human mitochondrial DNA (mtDNA), including its high copy number, maternal inheritance, lack of recombination, and high mutation rate, have made it the molecule of choice for studies of human population history and evolution.

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Human mtDNA is a circular genome of 16,569 base pairs and codes for thirty-seven genes. The human nuclear genome contains three billion base pairs and codes for possibly 30,000 genes.

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Organisms whose DNA sequence for a particular gene differs by only a few bases are likely to be closely related. This seems straightforward, but different parts of the genome mutate at different rates, and so scientists must select which region they wish to use. Ribosomal DNA (rDNA) mutates relatively slowly, and so can be used to examine the relationships between species that last shared a common ancestor hundreds of millions of years ago. However, mtDNA accumulates changes in the base sequence relatively rapidly, up to 10 times as fast as nuclear DNA. This means that it can be useful in studying the evolutionary history of species that diverged only recently, or to look at populations of the same species.

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The reasons for choosing mitochondrial DNA over nuclear DNA as the means to study human evolutionary principles are listed below.

  • It avoids recombination, although, research suggests that it can combine with the nuclear DNA. The mixing of already mixed sections from the mother and the father creates a garbled genetic history.
  • There are several thousand copies of mitochondrial DNA as compared to only two versions of the nuclear one.
  • Mitochondrial DNA is inherited maternally. Therefore, the tracking of the genetic line becomes easy. The traits are passed on from a great-grandmother to the grandmother, and to her daughter, and so on.
  • Its rate of mutation is much faster than nuclear DNA.
  • Mitochondrial DNA remains fossilized due to its sheer large numbers.
  • It is less likely to have degraded over time
  • It is more abundant (common)

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Once the fertilization process gets over, the coding region of mitochondrial DNA mutates at the rate of about 0.017×10-6/site/year. The hypervariable region is the one with no coding where the rate of mutation is 0.47×10-6. The rate of mutation of the whole genome is taken into consideration to determine the ancestry, while the descendants analysis reveals the changes in the mitochondrial genome.
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Focussing on the D-loop:

Evidence from DNA studies generally supports a recent African origin but these conclusions have been criticised for a lack of statistical support. One possible reason for this is because these studies have focussed mainly on the polymorphisms in a small section of the mitochondrial genome called the D-loop, which comprises around 7% of the mitochondrial genome. The reason for this section’s popularity lies in its particularly high mutation rate, meaning that scientists can analyse this relatively short sequence and still resolve differences between closely related sequences. Unfortunately, it is now becoming increasingly clear that this very high mutation rate is actually obscuring the informative information. Three main problems with data from the D-loop section have been identified:  •back mutation – sites that have already undergone substitution are returned to their original state

  • parallel substitution – mutations occur at the same site in independent lineages
  • rate heterogeneity – there is a large difference in the rate at which some sites undergo mutation when compared to other sites in the same region; data shows evidence of ‘hot spots’ for mutation.

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Tracing Ancestry with mtDNA:

In 1987 Rebecca Louise Cann, Mark Stoneking, and Allan Charles Wilson published “Mitochondrial DNA and Human Evolution” in the journal Nature. The authors compared mitochondrial DNA from different human populations worldwide, and from those comparisons they argued that all human populations had a common ancestor in Africa around 200,000 years ago.  She was given the name “Eve,” which was great for capturing attention, though somewhat misleading, as the name at once brought to mind the biblical Eve, and with it the mistaken notion that the ancestor was the first of our species—the woman from whom all humankind descended. The “Mitochondrial Eve” in question was actually the most recent common ancestor through matrilineal descent of all humans living today. That is, all people alive today can trace some of their genetic heritage through their mothers back to this one woman. In recent years, scientists have used mtDNA to trace the evolution and migration of human species, including when the common ancestor to modern humans and Neanderthals lived—though there has been considerable debate over the validity and value of the findings.

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Y chromosome:

The Y chromosome is responsible for determining male gender in mammals. The Y chromosome contains the SRY gene, which is necessary for the development of the testes in males. Without this gene, no testes would develop and a fetus would grow into a female. The Y chromosome which is found in the nucleus, is also uniparentally inherited, and is transmitted exclusively from father to son. The process of natural selection and genetic drift compels one to consider the male Y chromosome as a part of the detection, using the phylogenetic process. Despite the higher per-base-mutation rate of mtDNA, the much greater length of the Y chromosome offers the highest genealogical resolution of all non-recombining loci in the human genome. The Y chromosome contains the longest stretch of non-recombining DNA in the human genome and is therefore a powerful tool with which to study human evolution. Estimates of the time to the most recent common ancestor (TMRCA) of the Y chromosome have differed by approximately twofold from TMRCA estimates for the mitochondrial genome. Y chromosome coalescence time has been estimated in the range 50–115 ky, although larger values have been reported, whereas estimates for mitochondrial DNA (mtDNA) range from 150–240 ky. However, the quality and quantity of data available for these two uniparental loci have differed substantially. While the complete mitochondrial genome has been resequenced thousands of times, fully sequenced diverse Y chromosomes have only recently become available. Previous estimates of the Y chromosome TMRCA relied on short resequenced segments, rapidly mutating microsatellites, or single nucleotide polymorphisms (SNPs) ascertained in a small panel of individuals and then genotyped in a global panel. These approaches likely underestimate genetic diversity and, consequently, TMRCA.

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DNA dating (molecular genetic clock):

When scientists say that modern humans emerged in Africa about 200,000 years ago and began their global spread about 60,000 years ago, how do they come up with those dates? Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating. However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case. Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution. Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events. Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed. These changes accrue like the ticks on a stopwatch, providing a “molecular clock.” By comparing DNA sequences, geneticists cannot only reconstruct relationships between different populations or species but also infer evolutionary history over deep timescales. Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes. By applying these methods to the ever-growing database of DNA from diverse populations (both present-day and ancient), geneticists are helping to build a more refined timeline of human evolution.

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How DNA accumulates changes:

Molecular clocks are based on two key biological processes that are the source of all heritable variation: mutation and recombination.

Mutations are changes to the DNA code, such as when one nucleotide base (A, T, G or C) is incorrectly subbed for another. These changes will be inherited by future generations if they occur in eggs, sperm or their cellular precursors (the germline). Most result from mistakes when DNA copies itself during cell division, although other types of mutations occur spontaneously or from exposure to hazards like radiation and chemicals. In a single human genome, there are about 60 nucleotide changes per generation – minuscule in a genome made up of six billion letters. But in aggregate, over many generations, these changes lead to substantial evolutionary variation.  So as we go back on the family tree, there are more and more genetic differences between us and our ancestors. For example, there would be about 120 differences between your DNA and that of your four grandparents, and 180 differences between you and your eight great-grandparents, and so on. That enables us to make a prediction from the amount of genetic diversity between two species about the time since their common ancestor population lived. Scientists can use mutations to estimate the timing of branches in our evolutionary tree. First they compare the DNA sequences of two individuals or species, counting the neutral differences that don’t alter one’s chances of survival and reproduction. Then, knowing the rate of these changes, they can calculate the time needed to accumulate that many differences. This tells them how long it’s been since the individuals shared ancestors. Comparison of DNA between you and your sibling would show relatively few mutational differences because you share ancestors – mom and dad – just one generation ago. However, there are millions of differences between humans and chimpanzees; our last common ancestor lived over seven million years ago.

Recombination, also known as crossing-over, is the other main way DNA accumulates changes over time. It leads to shuffling of the two copies of the genome (one from each parent), which are bundled into chromosomes. During recombination, the corresponding (homologous) chromosomes line up and exchange segments, so the genome you pass on to your children is a mosaic of your parents’ DNA. Bits of the chromosomes from your mom and your dad recombine as your DNA prepares to be passed on. In humans, about 36 recombination events occur per generation, one or two per chromosome. As this happens every generation, segments inherited from a particular individual get broken into smaller and smaller chunks. Based on the size of these chunks and frequency of crossovers, geneticists can estimate how long ago that individual was your ancestor.

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Figure above shows gene flow between divergent populations leads to chromosomes with mosaic ancestry. As recombination occurs in each generation, the bits of Neanderthal ancestry in modern human genomes become smaller and smaller over time.  Neanderthal genes ‘survive in us’.  Between 1% and 4% of the Eurasian human genome seems to come from Neanderthals.

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Building timelines based on changes:

Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales. Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species. The recombination clock, on the other hand, ticks at a rate appropriate for dates within the last 100,000 years. These “recent” events (in evolutionary time) include gene flow between distinct human populations, the rise of beneficial adaptations or the emergence of genetic diseases. The case of Neanderthals illustrates how the mutation and recombination clocks can be used together to help us untangle complicated ancestral relationships. Geneticists estimate that there are 1.5-2 million mutational differences between Neanderthals and modern humans. Applying the mutation clock to this count suggests the groups initially split between 750,000 and 550,000 years ago. At that time, a population – the common ancestors of both human groups – separated geographically and genetically. Some individuals of the group migrated to Eurasia and over time evolved into Neanderthals. Those who stayed in Africa became anatomically modern humans.

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Figure above shows an evolutionary tree displaying the divergence and interbreeding dates that researchers estimated with molecular clock methods for these groups.  However, their interactions were not over: Modern humans eventually spread to Eurasia and mated with Neanderthals. Applying the recombination clock to Neanderthal DNA retained in present-day humans, researchers estimate that the groups interbred between 54,000 and 40,000 years ago. When scientists analyzed a Homo sapiens fossil, known as Oase 1, who lived around 40,000 years ago, they found large regions of Neanderthal ancestry embedded in the Oase genome, suggesting that Oase had a Neanderthal ancestor just four to six generations ago. In other words, Oase’s great-great-grandparent was a Neanderthal.

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Figure above compare chromosome 6 from the 40,000-year-old Oase fossil to a present-day human. The blue bands represent segments of Neanderthal DNA from past interbreeding. Oase’s segments are longer because he had a Neanderthal ancestor just 4–6 generations before he lived, based on estimates using the recombination clock.

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Anthropologists and geneticists had a problem. And the farther back in time they looked, the bigger the problem became.  For the past several years, there have been two main genetic methods to date evolutionary divergences – when our ancestors split from Neanderthals, chimpanzees, and other relatives. The problem was, the results of these methods differed by nearly two-fold. By one estimate, modern humans split from Neanderthals roughly 300,000 years ago. By the other, the split was closer to 600,000 years ago. Likewise, modern humans and chimps may have diverged around 6.5 or 13 million years ago. Puzzled by this wild disagreement, researchers with diverse expertise have been studying it from different angles. Their combined discoveries have shed light on how genetic differences accumulate over time and have advanced methods of genetic dating. Everyone alive today seems to share ancestors with each other just over 200,000 years ago and with Neanderthals between 765,000-550,000 years ago.

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In order to date these evolutionary splits, geneticists have relied on the molecular clock – the idea that genetic mutations accumulate at a steady rate over time. Specifically this concerns mutations that become neutral substitutions, or lasting changes to letters of the genetic code that do not affect an organism’s chances of surviving and reproducing. If such mutations arise clocklike, then calculating the time since two organisms shared common ancestors should be as easy as dividing the number of genetic differences between them by the mutation rate – the same way that dividing distance by speed gives you travel time.

For decades, anthropologists used fossil calibration to generate the so-called phylogenetic rate (a phylogeny is a tree showing evolutionary relationships). They took the geologic age of fossils from evolutionary branch points and calculated how fast mutations must have arisen along the resulting lineages. For example, the earliest fossils on the human branch after our split with chimps are identified by the fact that they seem to have walked on two legs; bipedalism is the first obvious difference that distinguishes our evolutionary lineage of hominins from that of chimps. These fossils are 7-6 million years old, and therefore the chimp-human split should be around that age. Dividing the number of genetic differences between living chimps and humans by 6.5 million years provides a mutation rate. Determined this way, the mutation rate is 0.000000001 (or 1×10-9) mutations per DNA base pair per year.  Applied to genomes with 6 billion base pairs, that means, over millions of years of chimp and human evolution, there have been on average six changes to letters of the genetic code per year. This rate can be used to date evolutionary events that are not evident from fossils, such as the spread of modern humans out of Africa.

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But genetic dating got messy in 2010, when improvements to DNA sequencing allowed researchers to determine the number of genetic differences between parents and their children. Known as pedigree analysis, this provides a more direct measurement of the current mutation rate within one generation, rather than an average over millions of years. When geneticists directly measure nucleotide differences between living parents and children (using human pedigrees), the mutation rate is half the other estimate: about 0.5×10⁻⁹ per site per year, or only about three mutations per year.  For the divergence between Neanderthals and modern humans, the slower rate provides an estimate between 765,000-550,000 years ago. The faster rate, however, would suggest half that age, or 380,000-275,000 years ago: a big difference. Resolving this disagreement propelled researchers to reassess and revise their starting assumptions:

How accurately were they counting the small number of differences between genomes of parents and children?

Were fossils assigned to the correct branches of the evolutionary tree?

And above all, how constant is the molecular clock?

It turns out that among primates, the molecular clock varies significantly by species, sex, and mutation type. A recent study found that New World monkeys (i.e. monkeys of the Americas like marmosets and squirrel monkeys) have substitution rates about 64% higher than apes (including humans). Within apes, rates are about 7% higher in gorillas and 2% higher in chimpanzees, compared to humans. But even among humans, mutation rates differ, particularly between the sexes with age. As fathers get older, they gain about one additional mutation per year in the DNA they can pass on to children. Mothers, on the other hand, accumulate considerably fewer mutations with each passing year.

These species and sex differences make sense when you consider how mutations form. Most heritable mutations occur from mistakes when DNA copies itself in the germline, or cells leading to eggs and sperm. The number of times germline DNA has to copy itself depends on developmental and reproductive variables including age at puberty, age at reproduction, and the process of sperm production. These traits vary across primates today, and certainly varied over primate evolution. For instance, average generation times are six years for New World monkeys, 19 years for gorillas, 25 years for chimps, and 29 years for humans. In human populations, the generation time typically ranges from 22 to 33 years.

And those extra mutations as fathers get older?

Sperm are produced continuously after puberty, so sperm made later in life are the result of more rounds of DNA replication and opportunities for replication errors. In contrast, a mother’s stock of eggs is formed by birth. The small increase with maternal age could be due to mutations from DNA damage, rather than replication errors.

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It’s now clear that one mutation rate cannot determine the dates for all divergences relevant to human evolution. However, researchers can secure the timeline for important evolutionary events by combining new methods of genetic dating with fossils and geologic ages.  Innovative computational methods have incorporated reproductive variables into calculations. By taking into account ages of reproduction in both sexes, age of male puberty, and sperm production rates, researchers have estimated split times that accord with the fossil record. Another new approach has analysed mutations that are mainly independent of DNA replication. It seems that certain classes of mutations, related to DNA damage, do behave more clocklike. And some researchers have focused on ancient DNA. Comparing human fossils from the past 50,000 years to humans today, suggests a mutation rate that agrees with pedigree analysis.

At least one evolutionary split was pinned down in 2016, after ancient DNA was extracted from 430,000 year-old hominin fossils from Sima de los Huesos, Spain. The Sima hominins looked like early members of the Neanderthal lineage based on morphological similarities. This hypothesis fit the timing of the split between Neanderthals and modern humans based on pedigree analysis (765,000-550,000 years ago), but did not work with the phylogenetic estimate (383,000-275,000 years ago).

Where do the Sima hominins belong on our family tree?

Were they ancestors of both Neanderthals and modern humans, just Neanderthals, or neither?

DNA answered this definitively. The Sima hominins belong to the Neanderthal branch after it split with modern humans. Moreover, the result provides a firm time point in our family tree, suggesting that the pedigree rate works for this period of human evolution. Neanderthals and modern humans likely diverged between 765,000-550,000 years ago. Other evolutionary splits may soon be clarified as well, thanks to advances brought about by the mutation rate debates.

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New approaches for better dating:

  1. One approach is to focus on mutations that arise at a steady rate regardless of sex, age and species. This may be the case for a special type of mutation that geneticists call CpG transitions by which the C nucleotides spontaneously become T’s. Because CpG transitions mostly do not result from DNA copying errors during cell division, their rates should be mainly independent of life history variables – and presumably more uniform over time. Focusing on CpG transitions, geneticists recently estimated the split between humans and chimps to have occurred between 9.3 and 6.5 million years ago, which agrees with the age expected from fossils. While in comparisons across species, these mutations seem to happen more like clockwork than other types, they are still not completely steady.
  2. Another approach is to develop models that adjust molecular clock rates based on sex and other life history traits. Using this method, researchers calculated a chimp-human divergence consistent with the CpG estimate and fossil dates. The drawback here is that, when it comes to ancestral species, we can’t be sure of life history traits, like age at puberty or generation length, leading to some uncertainty in the estimates.
  3. The most direct solution comes from analyses of ancient DNA recovered from fossils. Because the fossil specimens are independently dated by geologic methods, geneticists can use them to calibrate the molecular clocks for a given time period or population. This strategy recently resolved the debate over the timing of our divergence with Neanderthals. In 2016, geneticists extracted ancient DNA from 430,000-year-old fossils that were Neanderthal ancestors, after their lineage split from Homo sapiens. Knowing where these fossils belong in the evolutionary tree, geneticists could confirm that for this period of human evolution, the slower molecular clock rate of 0.5×10⁻⁹ provides accurate dates. That puts the Neanderthal-modern human split between 765,000 to 550,000 years ago. As geneticists sort out the intricacies of molecular clocks and sequence more genomes, we’re poised to learn more than ever about human evolution, directly from our DNA.

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SNP judgments:

Many current techniques for analyzing the genome rely on a form of genetic evidence called a SNP. SNP stands for single (S) nucleotide (N) polymorphism (P), and they’re everywhere — all over the human genome. SNPs are places where, in different people, the genetic sequence varies by a single nucleotide letter: A, T, G, or C, the alphabet of the genetic code. This genetic difference need not translate to a physical difference. For example, the fact that one person carries an A at a particular site while another person carries a G at that location may not affect them at all — or, depending on the SNP, it might cause a change that gives one of them a survival advantage. Whatever the effect on their carriers, SNPs can be used like archaeological artifacts to help reconstruct the history of the chromosomes in which they are embedded. The Harpending team used SNPs as markers to try to figure out which stretches of DNA had been traveling together as genetic hitchhikers.

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Stages of human evolution:

 

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Homo sapiens, the first modern humans, evolved from their early hominid predecessors about 250,000 years ago. Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa. The first modern humans began moving outside of Africa starting about 70,000-100,000 years ago. They developed a capacity for language about 50,000 years ago. Humans are the only known species to have successfully populated, adapted to, and significantly altered a wide variety of land regions across the world, resulting in profound historical and environmental impacts.

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Discoveries in Africa have yielded many remains of ancient human relatives. Such finds have cemented Africa’s status as the cradle of humanity — the place from which modern humans and their predecessors spread around the globe — and relegated Asia to a kind of evolutionary cul-de-sac.

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Homo sapiens is part of a group called hominids, which were the earliest humanlike creatures. Though there was a degree of diversity among the hominid family, they all shared the trait of bipedalism, or the ability to walk upright on two legs. Scientists have several theories about why early hominids evolved. One, the aridity hypothesis, suggests that early hominids were more suited to dry climates and evolved as the Africa’s dry savannah regions expanded. According to the savannah hypothesis, early tree-dwelling hominids may have been pushed out of their homes as environmental changes caused the forest regions to shrink and the size of the savannah expand. These changes, according to the savannah hypothesis, may have caused them to adapt to living on the ground and walking upright instead of climbing. One of the earliest defining human traits, bipedalism — the ability to walk on two legs — evolved over 4 million years ago. Other important human characteristics — such as a large and complex brain, the ability to make and use tools, and the capacity for language — developed more recently. Many advanced traits — including complex symbolic expression, art, and elaborate cultural diversity — emerged mainly during the past 100,000 years. Hominids continued to evolve and develop unique characteristics. Their brain capacities increased, and approximately 2.3 million years ago, a hominid known as Homo habilis began to make and use simple tools. By a million years ago, some hominid species, particularly Homo erectus, began to migrate out of Africa and into Eurasia, where they began to make other advances like controlling fire.  Between 70,000 and 100,000 years ago, Homo sapiens began migrating from the African continent and populating parts of Europe and Asia. For instance, they reached the Australian continent in canoes sometime between 35,000 and 65,000 years ago. When humans migrated from Africa to colder climates, they made clothing out of animal skins and constructed fires to keep themselves warm; often, they burned fires continuously through the winter. Sophisticated weapons, such as spears and bows and arrows, allowed them to kill large mammals efficiently. Along with changing climates, these hunting methods contributed to the extinction of giant land mammals such as mammoths, giant kangaroos, and mastodons. In addition to hunting animals and killing them out of self-defense, humans began to use the earth’s resources in new ways when they constructed semi-permanent settlements. Humans started shifting from nomadic lifestyles to fixed homes, using the natural resources there. Semi-permanent settlements would be the building-blocks of established communities and the development of agricultural practices.

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The incredible story of our evolution from ape ancestors spans 6 million years or more, and features the acquirement of traits from bipedal walking, large brains, hairlessness, tool-making, hunting and harnessing fire, to the more recent development of language, art, culture and civilisation. Darwin’s The Origin of Species, published in 1859, suggested that humans were descended from African apes. However, no fossils of our ancestors were discovered in Africa until 1924, when Raymond Dart dug up the “Taung child” – a 3-million to 4 million-year-old Australopithecine. Over the last century, many spectacular discoveries have shed light on the history of the human family. Somewhere between 12 and 19 different species of early humans are recognised, though paleoanthropologists bitterly dispute how they are related. Famous fossils include the remarkably complete “Lucy”, dug up in Ethiopia in 1974, and the astonishing “hobbit” species, Homo floresiensis, found on an Indonesian island in 2004. One famous member of the species Australopithecus afarensis is the remarkably complete fossil found by palaeaoanthropologist Donald Johanson in Hadar, Ethiopia in 1974. The 3.2-million-year-old fossil was named Lucy, after the Beatles’ song Lucy in the Sky with Diamonds. She stood around 1.1 metres (3.5 feet) tall and although she walked on two legs, she probably had a less graceful gait than us, since she walked with them bent. Hundreds of other fossils of Australopithecus afarensis have now also been discovered. Other related early human species include Australopithecus africanus – such as the Taung child – 3.5-million-year-old Kenyanthropus platyops, 5.8-million to 4.4-million-year-old Ardipithecus, 5.8-million-year-old Orrorin tugenensis and 6 million year old Sahelanthropus tchadensis.

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Australopithecines are thought to be the ancestors of Homo, the group to which our own species, Homo sapiens, belongs. However, Australopithecines may also have given rise to another branch of hominid evolution – the vegetarian Paranthropus species. Around 2.7 million years ago, species such as Paranthropus bosei in east Africa evolved to take advantage of the dry grasslands. This included the development of enormous jaws and chewing muscles for grinding up tough roots and tubers. By 2.4 million years ago, Homo habilis had appeared – the first recognisably human-like hominid to appear in the fossil record – which lived alongside P. bosei. Their bodies were around two-thirds the size of ours, but their brains were significantly larger than Australopithecines with a volume of about 600 cubic centimetres. H. habilis had much smaller teeth and jaws than Paranthropus and was probably the first human to eat large quantities of meat. This meaty diet, acquired through scavenging, may have provided energy required to kick-start an increasing brain size. A mutation that weakened jaw muscles and gave our brains more space to grow may also lie behind the big brains we have today. H. habilis – which means “handy man” – was also the first early human to habitually create tools and use them to break bones and extract marrow. This tool-making tradition, known as Oldowan, lasted virtually unchanged for a million years. Oldowan tools were made by breaking an angular rock with a “hammerstone” to give simple, sharp-edged stone flakes for chopping and slicing. Despite their own increases in brain size, the Paranthropus group of species had become extinct by 1.2 million years ago.

At around 1.65 million years ago, another early human, Homo ergaster, started to create tools in a slightly different fashion. This so-called Acheulean tradition was the tool-making technology used for nearly the entire Stone Age, and practiced until 100,000 years ago. Acheulean tools, such as hand axes and cleavers, were larger and more sophisticated than their predecessors’. They may have been status symbols as well as tools. Homo ergaster first appeared in Africa around 2 million years ago, and in many ways resembled us. Though they had brow ridges, they had lost the stoop and long arms of their ancestors. They may have been even more slender than us and were probably well-adapted to running long distances. Some experts believe that they were the first to sport largely hairless bodies, and to sweat, though another theory puts our hairlessness down to an aquatic phase. H.ergaster may have been the first early human to leave Africa. Bones dated to around 1.75 million years ago have been found in Dmanisi in Georgia. Shortly afterwards, Homo erectus appeared – the first early human whose fossils have been seen in large numbers outside of Africa. The first specimen discovered, a single cranium, was unearthed in Indonesia in 1891. H.erectus was highly successful, spreading to much of Asia between 1.8 and 1.5 million years ago, and surviving as recently as 27,000 years ago. This species, with a brain volume of around 1000 cubic-cm would have interacted with modern humans. They may have been the first people to take to the seas and habitually hunt prey such as mammoths and wild horses, although there is some debate about this. They may also have harnessed the use of fire and built the first shelters. In 2004, the remains of a tiny and mysterious human species, that may have lived as recently as 13,000 years ago, was discovered on an Indonesian island. More bones of the “hobbit”, or Homo floresiensis, were uncovered in 2005. Some studies suggest it had an advanced brain and was unequivocally a separate species – but others argue that these people were modern humans suffering from a genetic disorder.

Early human fossil evidence from Spain, dating to around 780,000 years ago, points to the first known Europeans. Stone tools have also been found in England from around 700,000 years ago, attributed to Homo antecessor or Homo heidelbergensis. More recently, 325,000-year-old H. heidelbergensis tracks were discovered preserved on an Italian volcano. Some of the biggest collections of hominid remains ever found are from Boxgrove in England and Atapuerca in Spain. Experts believe that these humans may have had ears equipped to detect nuances of human speech, whether or not they had simple language. Some palaeoanthropologists believe that H. heidelbergensis evolved into our own species in Africa, whilst in Europe, the Neanderthals emerged as a separate species. The Neanderthals were found across Europe, between 200,000 and 28,000 years ago. Though they still possessed pronounced brow ridges and were more thick-set, these people largely resembled us. They were as nimble-fingered, and matured at a similar age to us. Their brains were even slightly larger. It is not known if the Neanderthals had developed simple language. But they did possess some aspects of our culture, such as ritual burying of the dead; creating art; using tools to attack each other; and complex hunting methods – as evidenced by a remarkable butchery site in the UK.

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There are several competing theories about how all these early humans are related to us today.

Most widely accepted is the “Out of Africa” hypothesis. This holds that ancient humans evolved exclusively in Africa, then spread across the world in two migration waves. The migration of H. erectus across Eurasia made up the first wave. Later, our own species evolved in Africa and fanned out in a second wave 200,000 years ago. These new people totally replaced H. erectus in Asia and the Neanderthals in Europe. Advocates of the multiregional hypothesis instead believe that early humans started to leave Africa around 2 million years ago, and were never totally replaced by recent migrants. They believe these far-flung hominids exchanged genes and interbred, slowly evolving into modern humans – in many places, simultaneously. Through gene flow, modern characteristics such as large brains gradually spread, it is suggested. Some fossils seem to support the multiregional hypothesis. H. erectus skulls in Asia, for example, have similarly flat cheek and nasal regions as people there today do. Most – but not all – genetic evidence appears to back the Out of Africa hypothesis. There is surprisingly little variation in the mitochondrial DNA (mtDNA) of different people today, which suggest that humans evolved recently from a small ancestral population. In addition, the variation of mtDNA in Africans is greater than elsewhere, suggesting that people have been evolving there for longer. We may all be descended from a single African woman – dubbed Mitochondrial Eve – within the last 200,000 years. Male Y-chromosome DNA hints at a single male progenitor, too. Fewer than 50 people could have given rise to the entire population of Europe, experts believe.

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Human evolution is the process by which human beings developed on Earth from now-extinct primates. We are now the only living members of what many zoologists refer to as the human tribe, Hominini, but there is abundant fossil evidence to indicate that we were preceded for millions of years by other hominins, such as Australopithecus, and that our species also lived for a time contemporaneously with at least one other member of our genus, Homo neanderthalensis (the Neanderthals). In addition, we and our predecessors have always shared the Earth with other apelike primates, from the modern-day gorilla to the long-extinct Dryopithecus. That we and the extinct hominins are somehow related and that we and the apes, both living and extinct, are also somehow related is accepted by anthropologists and biologists everywhere. Yet the exact nature of our evolutionary relationships has been the subject of debate and investigation since the great British naturalist Charles Darwin published his monumental books On the Origin of Species (1859) and The Descent of Man (1871). Darwin never claimed, as some of his Victorian contemporaries insisted he had, that “man was descended from the apes,” and modern scientists would view such a statement as a useless simplification—just as they would dismiss any popular notions that a certain extinct species is the “missing link” between man and the apes. There is theoretically, however, a common ancestor that existed millions of years ago. This ancestral species does not constitute a “missing link” along a lineage but rather a node for divergence into separate lineages. This ancient primate has not been identified and may never be known with certainty, because fossil relationships are unclear even within the human lineage, which is more recent. In fact, the human “family tree” may be better described as a “family bush,” within which it is impossible to connect a full chronological series of species, leading to Homo sapiens, that experts can agree upon.

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Human timeline:

 

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The Miocene Epoch was characterized by major global climatic changes that led to more seasonal conditions with increasingly colder winters north of the Equator. By the Late Miocene, in many regions inhabited by apelike primates, evergreen broad-leaved forests were replaced by open woodlands, shrublands, grasslands, and mosaic habitats, sometimes with denser-canopied forests bordering lakes, rivers, and streams. Such diverse environments stimulated novel adaptations involving locomotion in many types of animals, including primates. In addition, there were a larger variety and greater numbers of antelope, pigs, monkeys, giraffes, elephants, and other animals for adventurous hominins to scavenge and perhaps kill. But large cats, dogs, and hyenas also flourished in the new environments; they not only would provide meat for scavenging hominins but also would compete with and probably prey upon them. In any case, our ancestors were not strictly or even heavily carnivorous. Instead, a diet that relied on tough, abrasive vegetation, including seeds, stems, nuts, fruits, leaves, and tubers, is suggested by primate remains bearing large premolar and molar teeth with thick enamel. Behaviour and morphology associated with locomotion also responded to the shift from arboreal to terrestrial life. The development of bipedalism enabled hominins to establish new niches in forests, closed woodlands, open woodlands, and even more open areas over a span of at least 4.5 million years. Indeed, obligate terrestrial bipedalism (that is, the ability and necessity of walking only on the lower limbs) is the defining trait required for classification in the human tribe, Hominini.

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It is generally agreed that the taproot of the human family shrub is to be found among apelike species of the Middle Miocene Epoch (16.4 to 11.2 million years ago) or Late Miocene Epoch (11.2 to 5.3 mya). Genetic data based on molecular clock estimates support a Late Miocene ancestry. Various Eurasian and African Miocene primates have been advocated as possible ancestors to the early hominins, which came on the scene during the Pliocene Epoch (5.3 to 2.6 mya). Though there is no consensus among experts, the primates suggested include Kenyapithecus, Griphopithecus, Dryopithecus, Graecopithecus (Ouranopithecus), Samburupithecus, Sahelanthropus, and Orrorin. Kenyapithecus inhabited Kenya and Griphopithecus lived in central Europe and Turkey from about 16 to 14 mya. Dryopithecus is best known from western and central Europe, where it lived from 13 to possibly 8 mya. Graecopithecus lived in northern and southern Greece about 9 mya, at roughly the same time as Samburupithecus in northern Kenya. Sahelanthropus inhabited Chad between 7 and 6 million years ago. Orrorin was from central Kenya 6 mya. Among these, the most likely ancestor of great apes and humans may be either Kenyapithecus or Griphopithecus. Among evolutionary models that stress the Eurasian species, some consider Graecopithecus to be ancestral only to the human lineage, containing Australopithecus, Paranthropus, and Homo, whereas others entertain the possibility that Graecopithecus is close to the great-ape ancestry of Pan (chimpanzees and bonobos) and Gorilla as well.

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During the Miocene epoch the family Hominoidea diverged into two sub-families the Pongidae (apes) and the Hominidae(humans).The exact point of divergence between the ape line and the human line is debatable. Dryopithecus is considered to be ancestor of both apes and humans by some experts.

Dryopithecus: This genus lived in Africa, China, India and Europe. The genetic title dryopithecus means oak wood apes because it is believed that the environmental conditions were such at that time with densely forested tropical lowlands and the members might have been predominantly herbivorous.

Ramapithecus: The first remains of Ramapithecus were discovered from Shivalik hills in Punjab and later discovered in Africa and Saudi Arabia. The region where Ramapithecines lived was not merely forest but open grassland. A hominid status for them is claimed on two grounds: Fossil evidence indicating adaptation including robust jaws, thickened tooth enamel and shorter canines.

Australopithecus: This genus is the immediate forerunner of the genus Homo. The first Australopithecine find was made in 1924 at Taung a limestone quarry site in South Africa by Raymond Dart. They walked erect, lived on the ground and probably used stones as weapons to hunt small animals. They weighed 60 to 90 pounds and were about 4 feet tall.

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Australopithecus afarensis

Nickname:  Lucy’s species

Where Lived:  Eastern Africa (Ethiopia, Kenya, Tanzania)

When Lived:  Between about 3.85 and 2.95 million years ago

Australopithecus afarensis is one of the longest-lived and best-known early human species—paleoanthropologists have uncovered remains from more than 300 individuals! Found between 3.85 and 2.95 million years ago in Eastern Africa (Ethiopia, Kenya, Tanzania), this species survived for more than 900,000 years, which is over four times as long as our own species has been around.  It is best known from the sites of Hadar, Ethiopia (‘Lucy’, AL 288-1 and the ‘First Family’, AL 333); Dikika, Ethiopia (Dikika ‘child’ skeleton); and Laetoli (fossils of this species plus the oldest documented bipedal footprint trails). Similar to chimpanzees, Au. afarensis children grew rapidly after birth and reached adulthood earlier than modern humans. This meant Au. afarensis had a shorter period of growing up than modern humans have today, leaving them less time for parental guidance and socialization during childhood.

Au. afarensis had both ape and human characteristics: members of this species had apelike face proportions (a flat nose, a strongly projecting lower jaw) and braincase (with a small brain, usually less than 500 cubic centimeters — about 1/3 the size of a modern human brain), and long, strong arms with curved fingers adapted for climbing trees. They also had small canine teeth like all other early humans, and a body that stood on two legs and regularly walked upright. Their adaptations for living both in the trees and on the ground helped them survive for almost a million years as climate and environments changed.

Year of Discovery: 1974

History of Discovery:

The species was formally named in 1978 following a wave of fossil discoveries at Hadar, Ethiopia, and Laetoli, Tanzania.  Subsequently, fossils found as early as the 1930s have been incorporated into this taxon.

Height: Males: average 4 ft 11 in (151 cm); Females: average 3 ft 5 in (105 cm)

Weight: Males: average 92 lbs (42 kg); Females: average 64 lbs (29 kg)

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To begin our study of the stages of man evolution, the earliest fossil hominid, Ardipithecus ramidus, is a recent discovery dating 4.4 million years ago. He was 4 feet tall and bipedal (having two feet). It is thought this species lived as forest dwellers. Australopithecus anamensis, a new species, was named in 1995 and was found in Kenya. This species lived between 4.2 and 3.9 million years ago, and its body showed advanced bipedal features, but the skull closely resembled the ancient apes.  Australopithecus afarensis discussed above. The Australopithecus africanus was similar to the afarensis, but lived between three and two million years ago. He was also bipedal and slightly larger in body size. His brain was not advanced for speech. The hominid was an herbivore and ate tough, hard to chew, plants. The shape of the jaw was human-like. The Australopithecus robustus lived between two and 1.5 million years ago. His body was similar to that of the africanus, but had a larger and more massive skull and teeth. His huge face was flat and had no forehead. He had no indication of speech capabilities.  The Australopithecus boisei lived between 2.1 and 1.1 million years ago. He was smaller than the robustus, but with a more massive face. He had huge molars, for which the largest measured 0.9 inches across. Some authorities believe the robustus and boisei are of the same species.

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The role of A. afarensis as the stem from which the other hominids arose is in some dispute. About 2 million years ago, after a long million year period of little change, as many as six hominid species evolved in response to climate changes associated with the beginning of the Ice Age. Two groups developed: the australopithecines, generally smaller brained and not users of tools; and the line that led to genus Homo, larger brained and makers and users of tools. The australopithecines died out 1 million years ago; Homo are still here!  With an incomplete fossil record, australopithecines, at least the smaller form, A. africanus, was thought ancestral to Homo. Recent discoveries however have caused a re-evaluation of that hypothesis. One pattern is sure, human traits evolved at different rates and at different times, in a mosaic: some features (skeletal, dietary) establishing themselves quickly, others developing later (toolmaking, language, use of fire).  A cluster of species developed about 2-2.5 million years ago in Africa. Homo had a larger brain and a differently shaped skull and teeth than the australopithecines.

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Evolution of Modern Humans: Evolution of genus Homo:

The evolution of the genus Homo took place mostly in the Pleistocene. The whole genus is characterised by its use of stone tools, initially crude, and becoming ever more sophisticated. So much so that in archaeology and anthropology the Pleistocene is usually referred to as the Palaeolithic, or the Stone Age.

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Homo habilis:

After researchers unearthed the australopithecines, the next major “missing link” to be found was Homo habilis, an early representative of modern humankind. Found by Louis and Mary Leakey at Olduvai Gorge in Tanzania, these fossils date to between 2.5 and 1.7 million years ago. This creature was bipedal, fully upright, and had the capacity to use forearms for handling tools and weapons. These fossil specimens show an increased brain size of 600 cubic centimeters (37 cubic inches), and a jaw and tooth size more closely resembling modern humans. Any residual physical traits for climbing had also disappeared. Cut marks on bones suggest the use of tools to prepare meat. They probably retained some of the skeletal characteristics of the australopithecines that made them great climbers. They may have spent considerable time in trees foraging, sleeping, and avoiding predators. They were the first of our relatives to have opposable thumbs, and the fossil skulls show physical traces of asymmetrical brain development, which is reflected in the way that stone tools were shaped. Homo habilis is also called The Handy Man because tools were found with his fossil remains. He existed between 2.4 and 1.4 million years ago. The brain shape shows evidence some speech had developed. He was 5’ tall and weighed about 100 pounds.

Homo habilis

Nickname:  Handy Man

Where Lived:  Eastern and Southern Africa

When Lived:  2.4 million to 1.4 million years ago

Year of Discovery: 1960

Height: average 3 ft 4 in – 4 ft 5 in (100 – 135 cm)

Weight: average 70 lbs (32 kg)

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The earliest documented representative of the genus Homo is Homo habilis, which evolved around 2.8 million years ago, and is arguably the earliest species for which there is positive evidence of the use of stone tools. The brains of these early hominins were about the same size as that of a chimpanzee, although it has been suggested that this was the time in which the human SRGAP2 gene doubled, producing a more rapid wiring of the frontal cortex. During the next million years a process of rapid encephalization occurred, and with the arrival of Homo erectus and Homo ergaster in the fossil record, cranial capacity had doubled to 850 cm^3. (Such an increase in human brain size is equivalent to each generation having 125,000 more neurons than their parents.) It is believed that Homo erectus and Homo ergaster were the first to use fire and complex tools, and were the first of the hominin line to leave Africa, spreading throughout Africa, Asia, and Europe between 1.3 to 1.8 million years ago.

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Figure above shows schematic representation of the emergence of H. sapiens from earlier species of Homo. The horizontal axis represents geographic location; the vertical axis represents time in millions of years ago (blue areas denote the presence of a certain species of Homo at a given time and place; late survival of robust australopithecines alongside Homo is indicated in purple). Based on Springer (2012), Homo heidelbergensis is shown as diverging into Neanderthals, Denisovans and H. sapiens. With the rapid expansion of H. sapiens after 60 kya, Neanderthals, Denisovans and unspecified archaic African hominins are shown as again subsumed into the H. sapiens lineage.

Homo sapiens is the only extant species of its genus, Homo. While some (extinct) Homo species might have been ancestors of Homo sapiens, many, perhaps most, were likely “cousins”, having speciated away from the ancestral hominin line. There is yet no consensus as to which of these groups should be considered a separate species and which should be a subspecies; this may be due to the dearth of fossils or to the slight differences used to classify species in the Homo genus.

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In May 2010, a new species, Homo gautengensis, was discovered in South Africa. Homo rudolfensis refers to a single, incomplete skull from Kenya. Scientists have suggested that this was another Homo habilis, but this has not been confirmed. Homo georgicus, from Georgia, may be an intermediate form between Homo habilis and Homo erectus, or a sub-species of Homo erectus.

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Homo ergaster:

Next in the story of human evolution, we find a group represented by Homo ergastor, a recently recognized African link between Homo habilis and Homo erectus. This group lived from about 1.8 million to 1 million years ago, when Homo erectus and other forms replaced it.  A fossil skeleton of Homo ergaster found in Kenya in 1984 became popularly known as Turkana Boy. This skull led researchers to believe this group may have been the first “naked ape.” This specimen suggested no body fur, a dark pigmented skin, and no evidence of living in trees. This species may have reached up to 1.8 meters (6 feet) in height; they appear to have had a near modern size brain and a striding gait. They may have been the first to make and wear clothing of some kind. Homo ergaster remains are distinguished from Homo erectus by differences in the shape of the skull such as lighter features, different shaped brow ridges and a higher brain cavity or cranial vault. Homo ergaster made stone tools, including well-made hand axes and cleavers for the butchering and processing of hunted animals. This technology appeared in Africa and was later carried into western Asia and Europe by Homo ergaster or its descendants. This technology was widespread and used until the end of the Early Stone Age, only a few hundred thousand years ago.

Homo ergaster exited Africa and dispersed into other parts of the Old World. Living in disparate geographical areas their morphology became diversified through the processes of genetic drift and natural selection.

  • In Asia these hominids evolved into Peking Man and Java Man, collectively referred to as Homo erectus.
  • In Europe and western Asia they evolved into the Neanderthals.

It now appears certain that Homo ergaster was the direct ancestor to the first inhabitants of Eurasia, including Homo erectus in the Far East, as well as the predecessor of Homo sapiens and Homo neanderthalensis in Europe. Homo ergaster led to Homo erectus, the famous missing link, which is our first ancestor to occupy territory from what is now northern China in Asia, to southern Great Britain and Spain in Europe, and all of Africa.

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Homo erectus:

Homo erectus, or upright man, lived between 1.8 million and 300,000 years ago. They were the earliest known humans with proportions similar to our own. They had short arms and long legs for living on the ground rather than in trees. Anthropologists studied Homo erectus’ teeth and discovered that Homo erectus grew at the same rate as a great ape. They used fire and made more sophisticated tools than Homo habilis. There is an ongoing debate regarding the classification, ancestry, and progeny of Homo erectus, especially in relation to Homo ergaster, with two major positions: 1) H. erectus is the same species as H. ergaster, and thereby H. erectus is a direct ancestor of the later hominins including Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens; or, 2) it is in fact an Asian species distinct from African H. ergaster.

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Soon after its origin (1.8 million but probably older than 2 million years ago) in Africa, Homo erectus appears to have migrated out of Africa and into Europe and Asia. Homo erectus differed from early species of Homo in having a larger brain size, flatter face, and prominent brow ridges. Homo erectus is similar to modern humans in size, but has some differences in the shape of the skull, a receding chin, brow ridges, and differences in teeth. Homo erectus was the first hominid to:

  1. provide evidence the social and cultural aspects of human evolution
  2. leave Africa (living in Africa, Europe, and Asia)
  3. use fire
  4. have social structures for food gathering
  5. utilize permanent settlements
  6. provide a prolonged period of growth and maturation after birth

Between 100,000 and 500,000 years ago, the world population of an estimated 1 million Homo erectus disappeared, replaced by a new species, Homo sapiens. How, when and where this new species arose and how it replaced its predecessor remain in doubt. Answering those questions has become a multidisciplinary task.

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Early African Homo erectus fossils are the oldest known early humans to have possessed modern human-like body proportions with relatively elongated legs and shorter arms compared to the size of the torso. These features are considered adaptations to a life lived on the ground, indicating the loss of earlier tree-climbing adaptations, with the ability to walk and possibly run long distances. Compared with earlier fossil humans, note the expanded braincase relative to the size of the face. The most complete fossil individual of this species is known as the ‘Turkana Boy’ – a well-preserved skeleton (though minus almost all the hand and foot bones), dated around 1.6 million years old.  Microscopic study of the teeth indicates that he grew up at a growth rate similar to that of a great ape. There is fossil evidence that this species cared for old and weak individuals. The appearance of Homo erectus in the fossil record is often associated with the earliest handaxes, the first major innovation in stone tool technology. Early fossil discoveries from Java (beginning in the 1890s) and China (‘Peking Man’, beginning in the 1920s) comprise the classic examples of this species. Generally considered to have been the first species to have expanded beyond Africa, Homo erectus is considered a highly variable species, spread over two continents (it’s not certain whether it reached Europe), and possibly the longest lived early human species – about nine times as long as our own species, Homo sapiens, has been around!

Year of Discovery: 1891

History of Discovery:

Eugène Dubois, a Dutch surgeon, found the first Homo erectus individual (Trinil 2) in Indonesia in 1891. In 1894, Dubois named the species Pithecanthropus erectus, or ‘erect ape-man.’ At that time, Pithecanthropus (later changed to Homo) erectus was the most primitive and smallest-brained of all known early human species; no early human fossils had even been discovered in Africa yet.

Height: Ranges from 4 ft 9 in – 6 ft 1 in (145 – 185 cm)

Weight: Ranges from 88 – 150 lbs (40 – 68 kg)

Homo erectus lived between 1.8 million and 300,000 years ago. Toward the end, his brain was that of the size of modern man, and definitely could speak. Erectus developed tools, weapons, fire, and learned to cook his own food. He travelled out of Africa into China and the Southeast Asia developing clothing for northern climates. He turned to hunting for his food, and only his head and face differed from modern man. Homo sapiens (archaic) lived during the period 200,000 to 500,000 years ago. He had speech capabilities; his skull was rounded with smaller features. The skeleton shows a stronger build than modern human, but well proportioned.

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H. cepranensis and H. antecessor:

These are proposed as species that may be intermediate between H. erectus and H. heidelbergensis.

  • H. antecessor is known from fossils from Spain and England that are dated 1.2 Ma–500 ka.
  • H. cepranensis refers to a single skull cap from Italy, estimated to be about 800,000 years old.

Homo Antecessor:

Homo antecessor, or pioneer man, lived in Europe at least 780,000 years ago, the earliest known Europeans. Homo antecessor had a modern-looking face but primitive teeth, brow ridges and foreheads. Anthropologist Jose Bermudez de Castro believes that Homo antecessor was the direct ancestor of both Neanderthals and modern humans. However, most anthropologists believe that modern humans and Neanderthals are descendants of either Homo erectus or Homo ergaster.

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H. heidelbergensis:

H. heidelbergensis (“Heidelberg Man”) lived from about 800,000 to about 300,000 years ago. Also proposed as Homo sapiens heidelbergensis or Homo sapiens paleohungaricus. They possessed larger brain cases and flatter faces that earlier human species. They were also the first human species to live in colder climates. Anthropologists believe that their short, wide builds help them conserve body heat. They are also the first known species to build simple shelters out wood and rock.

H. rhodesiensis, and the Gawis cranium:

H. rhodesiensis, estimated to be 300,000–125,000 years old. Most current researchers place Rhodesian Man within the group of Homo heidelbergensis, though other designations such as archaic Homo sapiens and Homo sapiens rhodesiensis have been proposed. In February 2006 a fossil, the Gawis cranium, was found which might possibly be a species intermediate between H. erectus and H. sapiens or one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is believed to be 500,000–250,000 years old. Gawis man’s facial features suggest its being either an intermediate species or an example of a “Bodo man” female

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Homo Floresiensis:

The fossils of Homo floresiensis were discovered on the Indonesian island of Flores in 2003. Homo floresiensis lived between 95,000 and 13,000 years ago. They had an extremely small stature and stood about 3 feet tall. They’ve been nicknamed hobbits after the diminutive race in J.R.R. Tolkien’s “The Lord of the Rings.”  H. floresiensis individuals stood approximately 3 feet 6 inches tall, had tiny brains, large teeth for their small size, shrugged-forward shoulders, no chins, receding foreheads, and relatively large feet due to their short legs. Despite their small body and brain size, H. floresiensis made and used stone tools, hunted small elephants and large rodents, coped with predators such as giant Komodo dragons, and may have used fire.  The diminutive stature and small brain of H. floresiensis may have resulted from island dwarfism—an evolutionary process that results from long-term isolation on a small island with limited food resources and a lack of predators. Pygmy elephants on Flores, now extinct, showed the same adaptation. The smallest known species of Homo and Stegodon elephant are both found on the island of Flores, Indonesia.  However, some scientists are now considering the possibility that the ancestors of H. floresiensis may have been small when they first reached Flores.

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Homo naledi:

In 2015, an amazing discovery from deep inside a cave in South Africa was announced. An impressive suite of researchers led by Dr. Lee Berger from the University of Witwatersrand in South Africa, had recovered one of the largest assemblages of fossil hominins – and it was a new species called Homo naledi. What makes them so striking is their hodge podge of physical characteristics; for instance, Homo naledi has a more human like collarbone (clavicle), legs, ankles, and feet, while sharing some features of the hands and pelvis with earlier species like Australopithecus afarensis. This unique combination of modern and ancestral traits can be found across the Homo naledi fossils and led researchers to initially speculate that they could be up to 2 million years old, although the team didn’t have a secure date for the fossils when they were first published. But on May 9, 2017, the research team announced two important new findings in the journal eLife.

The first is that even after Berger’s team recovered at least 15 individuals from the Dinaledi chamber of the Rising Star Cave System, they continued excavation in a second chamber in 2013 (the Lesedi chamber) and found 130 more fossils from 4 more individuals, including two adults and one child! One of the new fossils, a male nicknamed “Neo” after the Sesotho word for “gift”, is one of the most complete hominin fossils ever discovered.

The second is that a combination of six different dating techniques – including radiometrically dating flowstones in the cave that covered some of the Homo naledi remains, as well as directly dating a few of their teeth – yielded a surprising result. Dated at between 236,000 and 335,000 years old, Homo naledi would have been sharing the planet with Homo erectus and Homo heidelbergensis, and even our own species, Homo sapiens.  This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.

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Homo neanderthalensis: Homo sapiens neanderthalensis:

Nickname:  Neanderthal

Where Lived:  Europe and southwestern to central Asia

When Lived:  About 400,000 – 40,000 years ago

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Figure above shows a femur, or thigh bone, from a Neanderthal that was discovered in the Hohlenstein-Stadel cave in Germany.

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Neanderthals are our closest extinct human relative. Some defining features of their skulls include the large middle part of the face, angled cheek bones, and a huge nose for humidifying and warming cold, dry air. Their bodies were shorter and stockier than ours, another adaptation to living in cold environments. But their brains were just as large as ours and often larger – proportional to their brawnier bodies. Neanderthals made and used a diverse set of sophisticated tools, controlled fire, lived in shelters, made and wore clothing, were skilled hunters of large animals and also ate plant foods, and occasionally made symbolic or ornamental objects. There is evidence that Neanderthals deliberately buried their dead and occasionally even marked their graves with offerings, such as flowers. No other primates, and no earlier human species, had ever practiced this sophisticated and symbolic behavior. DNA has been recovered from more than a dozen Neanderthal fossils, all from Europe; the Neanderthal Genome Project is one of the exciting new areas of human origins research.

Height: Males: average 5 ft 5 in (164 cm); Females: average 5 ft 1 in (155 cm)

Weight: Males: average 143 lbs (65 kg); Females: average 119 lbs (54 kg)

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Emergence of Modern Human Beings:

The origin of modern humans is still controversial. Did Neanderthals evolve gradually into modern humans, or were they replaced by modern forms originating from a single population? The answer to that depends on the answer to the question of the origin of H. sapiens from H. erectus. The out-of-Africa hypothesis suggests Neanderthals were a separate species (H. neanderthalensis) replaced as modern humans (H. sapiens) spread from Africa. The regional continuity hypothesis suggests Neanderthals were a subspecies (H. sapiens neanderthalensis) that evolved into modern humans (H. sapiens sapiens). The debate centers on whether modern humans have a direct relationship with Homo erectus or the Neanderthal. Some researchers feel that modern humans originated separately in Asia, Europe, and Africa. Others feel that modern humans originated in Africa and after migrating into Europe and Asia they replaced the Neanderthals or archaic Homo sapiens found there.

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In a landmark study conducted in 1997, scientists examined the mitochondrial DNA of a Neanderthal fossil and a modern human. This analysis done by molecular biologists provides evidence about when two populations of people last had a common ancestor. The results concluded that it is unlikely that Neanderthals were related to modern humans. Instead it is thought that Neanderthals were a distinct species that evolved side-by-side with early Homo sapiens for hundreds of thousands of years. The scientists further calculated that, while Neanderthals and modern humans did indeed share a common ancestor, Homo ergastor, the two lineages had diverged sometime between 550,000 and 690,000 years ago.

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Earlier evidence from sequencing mitochondrial DNA suggested that no significant gene flow occurred between H. neanderthalensis and H. sapiens, and that the two were separate species that shared a common ancestor about 660,000 years ago. However, a sequencing of the Neanderthal genome in 2010 indicated that Neanderthals did indeed interbreed with anatomically modern humans circa 45,000 to 80,000 years ago (at the approximate time that modern humans migrated out from Africa, but before they dispersed into Europe, Asia and elsewhere). The genetic sequencing of a human from Romania dated 40,000 years ago showed that 11% of their genome was Neanderthal. This would indicate that this individual had a Neanderthal great grandparent, 4 generations previously. It seems that this individual has left no living descendants. Nearly all modern non-African humans have 1% to 4% of their DNA derived from Neanderthal DNA, and this finding is consistent with recent studies indicating that the divergence of some human alleles dates to one Ma, although the interpretation of these studies has been questioned.  Neanderthals and Homo sapiens could have co-existed in Europe for as long as 10,000 years, during which human populations exploded vastly outnumbering Neanderthals, possibly outcompeting them by sheer numerical strength.

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Denisovan:

In 2008, a small fossil finger bone was found at the Denisova Cave in the Altai mountains in southern Siberia. Nothing about the bone seemed unusual, and it was assumed to belong to one of the Neandertals living there in that time period, between 30,000 and 48,000 years ago. When the mitochondrial DNA of the bone was sequenced in May 2010 however, it belonged neither to a Neandertal nor to a modern human (Krause et al. 2010). Where Neanderthals differ from modern humans by an average of 202 positions in the mtDNA genome, the Denisovan individual differed from modern humans by an average of 385 positions. This means that the most recent common mtDNA ancestor of the Denisovan, Neandertals and modern humans lived an estimated 1,000,000 years ago (with a large error margin), about twice as old as the most recent common mtDNA ancestor of Neandertals and humans. There was speculation that the Denisovan might belong to a previously unknown species, but it was also possible that it belonged to a relic Homo erectus, or to a Neandertal that had retained an archaic mtDNA sequence, or even to a modern human. The Denisovan genome appears to have made a genetic contribution of about 4.8% (+/- 0.5%) to the genomes of living Melanesians. Interestingly, they did not contribute to the genomes of modern populations such as Han Chinese and Mongolians which live near Denisova now. The Denisovans obviously interbred with the ancestors of modern Melanesians at some point, but it seems unlikely to have happened at Denisova, which suggests that the Denisovans lived over a considerable area of eastern Asia.

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The flow of genes from Neanderthal populations to modern human was not all one way. Sergi Castellano of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has in 2016 reported that while Denisovan and Neanderthal genomes are more related to each other than they are to us, Siberian Neanderthal genomes show similarity to the modern human gene pool, more so than to European Neanderthal populations. The evidence suggests that the Neanderthal populations interbred with modern humans possibly 100,000 years ago, probably somewhere in the Near East.

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According to the recent African origin of modern humans theory, modern humans evolved in Africa possibly from Homo heidelbergensis, Homo rhodesiensis or Homo antecessor and migrated out of the continent some 50,000 to 100,000 years ago, gradually replacing local populations of Homo erectus, Denisova hominins, Homo floresiensis and Homo neanderthalensis.  Archaic Homo sapiens, the forerunner of anatomically modern humans, evolved in the Middle Paleolithic between 400,000 and 250,000 years ago. Recent DNA evidence suggests that several haplotypes of Neanderthal origin are present among all non-African populations, and Neanderthals and other hominins, such as Denisovans, may have contributed up to 6% of their genome to present-day humans, suggestive of a limited inter-breeding between these species. The transition to behavioral modernity with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago according to some anthropologists although others point to evidence that suggests that a gradual change in behavior took place over a longer time span.

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Homo sapiens:

Homo sapiens is the systematic name used in taxonomy (also known as binomial nomenclature) for anatomically modern humans, i.e. the only extant human species. The name is Latin for “wise man” and was introduced in 1758 by Carl Linnaeus (who is himself also the type specimen). Extinct species of the genus Homo are classified as “archaic humans”. This includes at least the separate species Homo erectus, and possibly a number of other species which are variously also considered subspecies of either H. sapiens or H. erectus. H. sapiens idaltu (2003) is a proposed extinct subspecies of H. sapiens from Ethiopia about 160,000 years ago who is argued to be the direct ancestor of all modern humans. The age of speciation of H. sapiens out of ancestral H. erectus (or an intermediate species such as Homo heidelbergensis) is estimated to have taken place at roughly 315,000 years ago. However, there is known to have been continued admixture from archaic human species until as late as some 30,000 years ago; this is also the time of disappearance of any surviving archaic human species, which were apparently absorbed by the recent Out-Of-Africa expansion of Homo sapiens beginning some 50,000 years ago. Extant human populations have historically been divided into subspecies, but since c. the 1980s all extant groups tend to be subsumed into a single species, H. sapiens, avoiding division into subspecies altogether.

Where Lived:  Evolved in Africa, now worldwide

When Lived:  About 200,000 years ago to present

The species that you and all other living human beings on this planet belong to is Homo sapiens. During a time of dramatic climate change 200,000 years ago, Homo sapiens evolved in Africa. Like other early humans that were living at this time, they gathered and hunted food, and evolved behaviors that helped them respond to the challenges of survival in unstable environments. Anatomically, modern humans can generally be characterized by the lighter build of their skeletons compared to earlier humans. Modern humans have very large brains, which vary in size from population to population and between males and females, but the average size is approximately 1300 cubic centimeters. Housing this big  brain involved the reorganization of the skull into what is thought of as “modern” — a thin-walled, high vaulted skull with a flat and near vertical forehead. Modern human faces also show much less (if any) of the heavy brow ridges and prognathism of other early humans. Our jaws are also less heavily developed, with smaller teeth. Scientists sometimes use the term “anatomically modern Homo sapiens” to refer to members of our own species who lived during prehistoric times.

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Homo sapiens (the adjective sapiens is Latin for “wise” or “intelligent”) evolved between 350,000 and 260,000 years ago. Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in intra-cranial volume expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests there was migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa. A subsequent migration (both within and out of Africa) eventually replaced the earlier dispersed H. erectus. This migration and origin theory is usually referred to as the “recent single-origin hypothesis” or “out of Africa” theory. Current evidence does not preclude some multiregional evolution or some admixture of the migrant H. sapiens with existing Homo populations. This is a hotly debated area of paleoanthropology. Modern humans emerged in Africa long before the Neanderthals became extinct in Europe. A dispersal of H. sapiens out of Africa occurred at about 60 ka, with modern humans reaching as far as Australia at that time. Humans arrived in the Americas only recently, at about 30-15 ka (Meltzer, 2003). The reasons for this late arrival are still unclear, but certainly during the most recent glacial maximum the climatic conditions were severe in eastern Siberia, the Bering Strait region, and the western portion of arctic North America.

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Current research has established that humans are genetically highly homogenous; that is, the DNA of individuals is more alike than usual for most species, which may have resulted from their relatively recent evolution or the possibility of a population bottleneck resulting from cataclysmic natural events such as the Toba catastrophe. Distinctive genetic characteristics have arisen, however, primarily as the result of small groups of people moving into new environmental circumstances. These adapted traits are a very small component of the Homo sapiens genome, but include various characteristics such as skin color and nose form, in addition to internal characteristics such as the ability to breathe more efficiently at high altitudes. Our early australopithecine ancestors in Africa probably had light skin beneath hairy pelts. If you shave a chimpanzee, its skin is light.  If you have body hair, you don’t need dark skin to protect you from ultraviolet [UV] radiation. After human ancestors shed most body hair, sometime before 2 million years ago, they quickly evolved dark skin for protection from skin cancer and other harmful effects of UV radiation. Then, when humans migrated out of Africa and headed to the far north, they evolved lighter skin as an adaptation to limited sunlight and pale skin synthesizes more vitamin D when light is scarce. Cheddar Man discovery shows that the genes for lighter skin became widespread in European populations far later than originally thought – and that skin colour was not always a proxy for geographic origin in the way it is often seen to be today. This also proves that so called racial categories are really very modern constructions, or very recent constructions, that are not applicable to the past at all.

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Summary of hominin evolution:

 

Figure above is highly simplified summary of hominin evolution over the past 8 Ma—the numerous terminating “twigs” schematically illustrate evolutionary “dead-ends.

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Summary of major evolutionary events in human evolution are:

  1. The split from chimpanzees at 8-6 Ma.
  2. The development of bipedal locomotion, probably occurring at the split.
  3. The slow evolutionary change to bigger teeth, thicker enamel, and reduction of canines that characterize a 5-Ma-long lineage from Sahelanthropus and Orrorin (if those are not the same as Ardipithecus), through Ardipithecus, to Australopithecus, and finally to Paranthropus.
  4. A splitting event between 3 and 2.5 Ma that produced Homo from an Australopithecus ancestor.
  5. The development of stone tool technology at about 2.6 Ma.
  6. The origin of a more carnivorous species, Homo erectus, at about 1.9 Ma.
  7. The first dispersal by hominins out of Africa, by 1.8 Ma.
  8. The development of the Acheulean stone tool culture at about 1.6 Ma.
  9. An increase in cranial capacity in H. heidelbergensis at about 500 ka.
  10. The origin of Homo sapiens at about 200 ka.
  11. The origin of symbolic language.
  12. The successive innovations in culture and lifestyle that led to the second dispersal event out of Africa at about 60 ka.
  13. Expression of symbolic language in cave paintings and sculptures by about 60-30 ka.
  14. The domestication of plants and animals within the last tens of thousands of years in different parts of the world.
  15. The ever-accelerating spread and dominance of humans over global ecosystems in the last few thousand years.

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How have we changed since our species first appeared?

Human evolution did not stop when our own species appeared. We have undergone change since our species first evolved. Some changes were universal whereas others were more regional in effect. The changes apparent in worldwide populations include a decrease in both overall body size and brain size as well as a reduction in jaw and tooth proportions. Regional populations have also evolved different physical and genetic characteristics in response to varying climates and lifestyles.  Physical and genetic changes have occurred within our species and will continue to occur at a basic level as new genes evolve. However, these changes may not be as dramatic as they were in the past as the situation today does not favour the evolution of a new human species.

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Humans today show an enormous diversity in appearance, however this diversity was not apparent in early Homo sapiens. Early members of our species lived in Africa and had evolved physical characteristics that were similar to each other in order to survive in that climate. When humans started to spread to different parts of the world about 70,000 years ago, they encountered a variety of different climatic conditions and evolved new physical adaptations more suitable to those new climates. Recent DNA studies (since 2007) confirm that genetic traits have changed or adapted to new environments during this time. In fact, the rate of change of DNA, and thus the rate of evolution, has accelerated in the last 40,000 years. Areas of the human genome still seem to be undergoing selection for things such as disease and skin colour. Physical characteristics such as skin and eye colour, hair type and colour and body shape are determined by genetics, but can also be influenced by the environment. Over long periods of time, the environment will act on the genes to develop particular characteristics within a population.

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Even H. sapiens that lived 10,000 years ago are not the same as those that inhabit Earth today. A comprehensive scan of the human genome has revealed that hundreds of human genes have undergone positive natural selection during the past 10,000 years of human evolution, including changes in bone development, skeleton, brain size, and carbohydrate metabolism (Evans 2005; Mekel-Bobrov 2005; Voight et al. 2006). The most obvious example of recent man-made “artificial evolution” is gluten tolerance, which allows humans to digest proteins in wheat. Approximately 10,000 years ago, before humans began farming and domesticating animals, people were unable to digest wheat (Greco 1997). Another example of recent artificial evolution is the loss of “hyperfocus”, or ADHD-related traits. Most humans are adapted to farming cultures; however, individuals with ADHD retained some of the older characteristics of the hunter gatherer societies that preceded agriculture (Hartmann 2005). The studies of isolated nomads in Kenya and the frequency of genetic variants that contribute to ADHD indicate that the trait provided a survival advantage in the past (Arcos-Burgos & Acosta 2007).

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Anatomical changes in evolution:

Human evolution from its first separation from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental, physiological, and behavioral changes. The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny (gestation and infancy), and decreased sexual dimorphism.

Homo sapiens is the result of four major evolutionary changes. These can be summarised as trends involving the development of:

  1. bipedalism (walking upright on two legs)
  2. shorter jaws with smaller teeth
  3. larger brains
  4. increasingly complex forms of technology

Fossil evidence shows that our ancestors became bipeds first, followed by changes to the teeth and jaws. It was only much later that our larger brains and more complex technology set us apart as Homo sapiens.

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Bipedalism:

Bipedalism is the basic adaptation of the hominid and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominids. The earliest hominin, of presumably primitive bipedalism, is considered to be either Sahelanthropus or Orrorin, both of which arose some 6 to 7 million years ago. The non-bipedal knuckle-walkers, the gorilla and chimpanzee, diverged from the hominin line over a period covering the same time, so either of Sahelanthropus or Orrorin may be our last shared ancestor. Ardipithecus, a full biped, arose somewhat later. The early bipeds eventually evolved into the australopithecines and still later into the genus Homo. There are several theories of the adaptation value of bipedalism. It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion, enabled long distance running and hunting, provided an enhanced field of vision, and helped avoid hyperthermia by reducing the surface area exposed to direct sun; features all advantageous for thriving in the new savanna and woodland environment created as a result of the East African Rift Valley uplift versus the previous closed forest habitat.  A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking.  However, recent studies suggest that bipedality without the ability to use fire would not have allowed global dispersal. This change in gait saw a lengthening of the legs proportionately when compared to the length of the arms, which were shortened through the removal of the need for brachiation. Another change is the shape of the big toe. Recent studies suggest that Australopithecines still lived part of the time in trees as a result of maintaining a grasping big toe. This was progressively lost in Habilines.

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Our bipedal body structure is unique amongst living apes. In fact, our ancestors started on the path to becoming human when they began walking on two legs. About seven million years ago, our early ancestors climbed trees and walked on four legs when on the ground. By five million years ago, our ancestors had developed the ability to walk on two legs but their gait was quite different from our own and their skeletons retained some features that helped them climb trees. By 1.8 million years ago, our ancestors had developed long legs and an efficient striding gait that made it easier to travel longer distances. Our ancestors had also developed the ability to run. This new stride became possible when changes to the shoulders, chest and waist allowed the body to stay balanced during prolonged running.

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Shorter jaws with smaller teeth:

As our ancestors evolved, their jaws and teeth changed in many ways. Some tooth changes were apparent five million years ago and additional changes have occurred since then. About seven million years ago our early ancestors had long jaws which resulted in projecting face profiles. They also had long, pointed canines and parallel tooth rows. By 5.5 million years ago, our ancestors’ canines were starting to become smaller. By 3.5 million years ago, our ancestors’ teeth were arranged in rows that were slightly wider apart at the back than at the front. By 1.8 million years ago, our ancestors’ canines had become short and relatively blunt like ours. Their jaws had also become much shorter. This made the face more vertical and forced the side rows of teeth to bend into a rounded arc shape. By 250,000 years ago, our direct ancestors had very short jaws and had developed a pointed chin for added strength. To fit into the small jaw, the teeth were now smaller and arranged in a tightly parabolic arc. Faces were now vertical rather than projecting.

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Figure above shows brain size and tooth size in hominins.

Brain size began to increase about two million years ago and this may be linked to improved diets containing more meat. Isotope studies on teeth suggest meat was becoming a significant part of some hominin diets by about 2.5 million years ago. Improved technology and a greater reliance on meat in the diet may have affected tooth size since foods now needed to be chewed less. This is reflected in the reduced size of the premolars and molars – the teeth responsible for grinding food.

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Sexual dimorphism:

The reduced degree of sexual dimorphism in humans is visible primarily in the reduction of the male canine tooth relative to other ape species (except gibbons) and reduced brow ridges and general robustness of males. Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans and bonobos are the only apes in which the female is fertile year round and in which no special signals of fertility are produced by the body (such as genital swelling during estrus). Nonetheless, humans retain a degree of sexual dimorphism in the distribution of body hair and subcutaneous fat, and in the overall size, males being around 15% larger than females. These changes taken together have been interpreted as a result of an increased emphasis on pair bonding as a possible solution to the requirement for increased parental investment due to the prolonged infancy of offspring.

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Ulnar opposition:

The ulnar opposition – the contact between the thumb and the tip of the little finger of the same hand – is unique to anatomically modern humans. In other primates the thumb is short and unable to touch the little finger. The ulnar opposition facilitates the precision grip and power grip of the human hand, underlying all the skilled manipulations.

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Other changes:

A number of other changes have also characterized the evolution of humans, among them an increased importance on vision rather than smell; a smaller gut; loss of body hair; evolution of sweat glands; a change in the shape of the dental arcade from being u-shaped to being parabolic; development of a chin (found in Homo sapiens alone); development of styloid processes; and the development of a descended larynx.

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Encephalization:

The human species eventually developed a much larger brain than that of other primates—typically 1,330 cm^3 in modern humans, nearly three times the size of a chimpanzee or gorilla brain. After a period of stasis with Australopithecus anamensis and Ardipithecus species, the pattern of encephalization started with Homo habilis, whose 600 cm^3 brain was slightly larger than that of chimpanzees. This evolution continued in Homo erectus with 800–1,100 cm^3, and reached a maximum in Neanderthals with 1,200–1,900 cm^3, larger even than modern Homo sapiens. This brain increase manifested during postnatal brain growth, far exceeding that of other apes (heterochrony). It also allowed for extended periods of social learning and language acquisition in juvenile humans, beginning as much as 2 million years ago.

 

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A primary motivation for understanding evolutionary changes in brain size, or encephalization, is to understand what evolutionary pressures have led to the large brain and complex cognition of humans. Across vertebrates, variation in total and relative brain size across mammals is marked, and is assumed to have a functional basis, because brains are metabolically costly. The brain of a modern human consumes about 20 watts (411 kilocalories per day), a fifth of the body’s resting power consumption. As species should be expected to maximize the cost-benefit ratio of supporting costly tissues, encephalization should be associated with significant advantages. A large and expanding literature has identified associations between relative brain size among extant species and ecological and behavioral correlates, including social characteristics, ecological flexibility, resilience , innovation, and social learning. Paleoneurologists agree that increased encephalization is an important dynamic of human brain evolution. However, brain evolution involved more than brain expansion. It also involved reorganization to support specific, uniquely human cognitive tasks, including those involved in linguistic processing and a highly developed facility for manufacturing and manipulating tools. Nevertheless, despite more than a century of effort, there is little consensus about how and when such reorganization occurred. One approach to exploring functional reorganization of the brain in humans has been the analysis of impressions of the brain’s surface convolutions (sulci and gyri) on the inner table of the endocranium. However, endocranial markings are notoriously difficult to identify reliably. Even where the impressions are fairly clear, taphonomic processes may distort the evidence. In addition, the functional correlates of the brain’s surface convolutions, especially in fossils, are literally superficial. Cognitive functions occur through internal connections among brain regions, as well as through the distribution of neuroreceptors that cannot be detected by examining the surface of the brain, let alone from endocranial markings. Therefore, functional inferences based on sulcal patterns are problematic.

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Various studies have demonstrated that hominids have increasingly devoted energy toward brainpower during evolution (Leonard & Robertson 1992; Navarrete et al. 2011). Furthermore, the brain-to-body size ratio is used for comparing and estimating an animal’s general intelligence or cognition.

The encephalisation quotient (EQ) is a measurement of the relative brain size, which is defined as the ratio of the actual to the predicted brain mass of an animal of a given size (Schmidt-Nielsen 1984), and is calculated using the equation:

The EQ (brain-to-body-size ratio) is an effective tool for estimating the intelligence of a wide variety of species, but whole brain size is a better tool for measuring the intelligence of related species (Deaner et al. 2007; Reader & Laland 2002). A correlation between the intelligence quotient and brain size has also been shown in humans (Willerman et al. 1991); however, researchers have debated about the oversimplification of this association caused by using simple brain size as a measure of intelligence in humans, due to controversial definitions of intelligence/IQ and complex racial issues (Neisser 1997; Mackintosh 2011). Nonetheless, it is clear that humans have become smarter during the evolution from their ape-like hominid ancestors, which lived seven million years ago, to Neanderthals:

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The human brain has grown from the size of chimpanzee brains to that of early hominid brains and finally to the size of Neanderthal brains. The size increased slowly during the first two-thirds of its evolution. Beginning two million years ago, a modest increase in brain size occurred (Buckner & Krienen 2013). In general, for the human species as a whole, we can state that the brain is related to intelligence and that the evolution of this particular organ is linked to the evolution of human intelligence (Roth & Dicke 2005). Numerous changes involving various genes have occurred in the last 10,000 years, and countless changes, particularly those involving the brain, have occurred in the five to seven million years of hominid evolution from Sahelanthropus to H. neanderthalensis. Previous studies have suggested that technologies and innovation would have played an evolutionary role alongside the evolution of hominids (Washburn 1959). In particular, the evolution of the human brain is distinct from other evolutionary processes, because free and usable limbs and tools had an impact on the survival of the hominid species (Darwin 1871). Hominids were talented throwers and waders. Sharpened bones/stones, spears, and fire became the insurmountable fangs of hominids. This intervention by artificial, hominid-generated forces would have served humans well. The knowledge of how to make tools, or the tools themselves, would be passed down from generation to generation to assist in feeding and protecting the family. Consequently, hominids would have evolved to adapt to changes in the environment that had been shaped by Paleolithic innovations and new industries .

Tools or the brain: which came first?

Some scholars have stated that the increase in brain size allowed the development of complex tools and innovations, whereas others have claimed that tool use influenced human evolution. The chain of causation would have operated in both directions, but which came first remains debatable. The link between the evolution of tools, including fire, provisioning, and the evolution of the brain is a two-way process, and thus attempting to determine the first event in a circular cause-and-effect process is futile.

The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are apparent in great apes although in less sophisticated forms than found in humans, such as great ape language.

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Human brain size evolved gradually over three million years, researchers say in 2018 study:

Ninety-four fossils from 13 different species believed to be human ancestors were analysed as part of the study. The team compared published research data on the skulls of 94 fossil specimens, beginning with Australopithecus – the earliest human ancestors from 3.2 million years ago – to pre-modern species including Homo erectus from 500,000 years ago, when brain size began to overlap with that of modern-day humans. The analysis revealed average brain size increased gradually over three million years. The findings showed the increase in brain size was mainly driven by the evolution of larger brains of individual hominin species within the populations, although extinction of smaller-brained species and introduction of larger-brained species may have played a part. Bernard Wood, professor of human origins at the George Washington University and senior study author, said: “The conventional wisdom was that our large brains had evolved because of a series of step-like increases, each one making our ancestors smarter. Not surprisingly the reality is more complex, with no clear link between brain size and behaviour.”

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Use of tools:

The use of tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution, especially the continued expansion of the human brain. Increased tool use would allow hunting for energy-rich meat products, and would enable processing more energy-rich plant products. Researchers have suggested that early hominins were thus under evolutionary pressure to increase their capacity to create and use tools. Precisely when early humans started to use tools is difficult to determine, because the more primitive these tools are (for example, sharp-edged stones) the more difficult it is to decide whether they are natural objects or human artifacts. There is some evidence that the australopithecines (4 Ma) may have used broken bones as tools, but this is debated.

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It should be noted that many species make and use tools, but it is the human genus that dominates the areas of making and using more complex tools. The oldest known tools are the Oldowan stone tools from Ethiopia, 2.5–2.6 million years old. A Homo fossil was found near some Oldowan tools, and its age was noted at 2.3 million years old, suggesting that maybe the Homo species did indeed create and use these tools. It is a possibility but does not yet represent solid evidence. The third metacarpal styloid process enables the hand bone to lock into the wrist bones, allowing for greater amounts of pressure to be applied to the wrist and hand from a grasping thumb and fingers. It allows humans the dexterity and strength to make and use complex tools. This unique anatomical feature separates humans from apes and other nonhuman primates, and is not seen in human fossils older than 1.8 million years.

Stone tools:

Stone tools are first attested around 2.6 Million years ago, when H. habilis in Eastern Africa used so-called pebble tools, choppers made out of round pebbles that had been split by simple strikes. This marks the beginning of the Paleolithic, or Old Stone Age; its end is taken to be the end of the last Ice Age, around 10,000 years ago. The Paleolithic is subdivided into the Lower Paleolithic (Early Stone Age), ending around 350,000–300,000 years ago, the Middle Paleolithic (Middle Stone Age), until 50,000–30,000 years ago, and the Upper Paleolithic, (Late Stone Age), 50,000-10,000 years ago. Archaeologists working in the Great Rift Valley in Kenya claim to have discovered the oldest known stone tools in the world. Dated to around 3.3 million years ago, the implements are some 700,000 years older than stone tools from Ethiopia that previously held this distinction. The period from 700,000–300,000 years ago is also known as the Acheulean, when H. ergaster (or erectus) made large stone hand axes out of flint and quartzite, at first quite rough (Early Acheulian), later “retouched” by additional, more-subtle strikes at the sides of the flakes. After 350,000 BP the more refined so-called Levallois technique was developed, a series of consecutive strikes, by which scrapers, slicers (“racloirs”), needles, and flattened needles were made. Finally, after about 50,000 BP, ever more refined and specialized flint tools were made by the Neanderthals and the immigrant Cro-Magnons (knives, blades, skimmers). In this period they also started to make tools out of bone.

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Figure above shows replica stone tools of the Acheulean industry, used by Homo erectus and early modern humans, and of the Mousterian industry, used by Neanderthals. (Top, left to right) Mid-Acheulean bifacial hand ax and Acheulean banded-flint hand ax. (Centre) Acheulean hand tool. (Bottom, left to right) Mousterian bifacial hand ax, scraper, and bifacial point.

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Complex technology:

Our ancestors have been using tools for many millions of years. As our ancestors’ intelligence increased, they developed the ability to make increasingly more complex stone, metal and other tools, create art and deliberately produce and sustain fire.

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Stone tools offer insights into history of human evolution:

Researchers suggest that hominins in India may have developed a Middle Palaeolithic culture phase around 385,000 years ago. Based on the study of over 7,200 stone artefacts collected from the archaeological site at Attirampakkam in the Kortallayar river basin about 60 km from Chennai, researchers suggest that hominins in India may have developed a Middle Palaeolithic culture phase around 385,000 years ago and continuing up to around 172,000 years ago.  According to earlier evidence, the Middle Palaeolithic culture in India was dated to around 125,000 years ago.  The Middle Palaeolithic is an important cultural phase, associated as it is globally with both modern humans and Neanderthals or other archaic hominins, with complex histories of interaction, cultural transitions and change and dispersals.  Based on stone tool and fossil studies, the Middle Palaeolithic culture (called the Middle Stone Age in Africa) is associated with modern humans in Africa, while it is associated with both modern humans and Neanderthals in Israel. But in Europe, the Middle Palaeolithic culture is associated only with Neanderthals.

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Fire:

Bones found in the Swartkrans Cave in South Africa, and dating back perhaps 1.5 million years ago, provide some of the earliest evidence for the use of fire. Analysis of the bones showed that they had been heated to the high temperatures normally associated with hearths. (Bush fires reach lower temperatures and do not generate the same changes to the bone.) Two hominins were present in Swartkrans at this time: Homo erectus and Paranthropus robustus , and it’s not known which species burnt the bones. However, later sites where fire was used are definitely associated with erectus. Hearth sites 790,000 years old, found in Israel, also contain the Acheulean tools produced by erectus.  Prior to these discoveries in Africa and Israel, the earliest site with evidence of regular use of fire was Zhoukoudian (Choukoudian), or “Dragon Bone Hill”, near Beijing. Here researchers studying “Peking Man” (Homo erectus ) found charcoal, charred bones, and rocks cracked by exposure to fire. Many of the bones belonged to large game animals, which may mean that the local erectus population was engaging in organised hunts.  Learning to use fire in a controlled manner was a major step for our ancestors, because it gave them greater control over their environment and also had the potential to make available a far greater range of foods. Fire would not only offer protection from predators, but would also allow its users to survive in much colder environments. In addition, the controlled use of fire is evidence of the ability to plan ahead, and would also have aided social interactions as people gathered round the hearth. Fire control was one of the most important cultural conquests in human evolution. The oldest evidence of this control goes back 400,000 years. Mastery of fire represented a true revolution in primitive communities. The first hominids to master fire were, in all certainty, Homo heidelbergensis, in Europe and possibly Homo erectus in Asia.

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How do we know what they ate?

The foods eaten by our ancestors can tell us a lot about their lifestyles and the environments in which they lived. Food has also played a major role in human evolution, particularly when meat became a significant part of the human diet about two million years ago. Clues about our ancestors’ diets are found in their teeth, bones and archaeological remains.

  1. Looking at teeth shape and size

Mammals have different types of teeth used for different functions, particularly (but not always) related to eating food. For example, incisors are primarily used for cutting or ripping, canines for tearing or holding, and premolars and molars for crushing and chewing. By looking at the size and shape of a hominin’s teeth, scientists can gain a clearer view about their basic diet. However, using form and structure of the teeth as a diet-predictor can be misleading, as more detailed studies (such as tooth wear or chemical analysis) indicate.

Making a mark: tooth wear patterns

Teeth are the hardest part of the skeleton but the particles in foods are still capable of leaving scratches and other marks on the surfaces of teeth. Different types of food will leave different kinds of marks. Scientists compare the marks left on fossil teeth with those found on the teeth of modern-day animals to reconstruct the prehistoric diets of our ancestors. Harder foods, such as nuts, seeds, tough fruits and tubers tend to leave small pit marks in the enamel that covers the tooth surface, whereas softer leaves and fruits leave many small scratches.

For example:

A 2008 study on tooth wear patterns of Paranthropus boisei revealed light, wispy scratches more similar to the marks on the teeth of modern fruit eaters than those on the teeth of modern primates. This suggests that P. boisei ‘s huge jaw, massive chewing muscles and flat, tough teeth where not primarily used to crush tough roots and nuts as was once believed. Tougher plants may have been used as a fallback diet when hard times meant other soft foods were unavailable.  Australopithecus africanus skulls show tooth wear like modern fruit eaters and appears to have eaten mostly soft plant foods like fruits and young leaves. It may also have included some meat in its diet.

  1. Chemical analysis of skeletons

Teeth and bones contain a protein called collagen, which absorbs chemical elements such as nitrogen, carbon, calcium and strontium from the food that an individual eats. Different types of foods contain these elements in different ratios so scientists are able to obtain information about our ancestors’ diets by studying the chemical elements found in fossilised bones and teeth. The ratios of these various elements are then compared with those of various modern-day animals to establish the types of foods eaten by our ancestors.

For example:

Paranthropus robustus lived between 1 and 2.3 million years ago. Tooth wear analysis suggests this species mostly ate hard plant foods such as nuts, seeds, roots and tubers, typical of the African open savanna. Chemical analysis on the ratio of strontium to calcium in their teeth suggests however, that this species may have also included some meat in their diet. The fossilised bones of Neanderthals (Homo neanderthalensis) contain different forms, or isotopes, of nitrogen- nitrogen-15 and nitrogen-14. The high ratio of nitrogen-15 to nitrogen-14 found in Neanderthal bones is similar to that found in the bone collagen of modern-day carnivores such as wolves. This indicates that the Neanderthal diet included a large amount of meat and little plant material.

  1. The archaeological record of diet

The remains left behind after food is collected, prepared and eaten also provide information about diet. These remains include food scraps as well as the artefacts used to collect and process foods. The chance that any remains from a prehistoric ‘dinner’ will survive varies depending on the types of food eaten. Foods with hard parts that are discarded rather than eaten (such as bones and shells) have a better chance of becoming preserved. Stone tools, bone fish hooks and other artefacts made from hard materials that do not readily decay will also preserve well. Vegetable matter, on the other hand, tends to decay more easily and is unlikely to leave any remains.

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Fossil Stable isotope analysis:

Stable isotopes are alternative forms of elements with different molecular weights that are found naturally and do not decay radioactively. Stable isotope analysis of elements such as carbon, nitrogen and sulphur is used in ecology to trace the flow of nutrients through food webs and assess trophic levels. Stable isotope analysis of fossil materials has become an increasingly important method for gathering dietary and environmental information from extinct species in terrestrial and aquatic ecosystems. The benefits of these analyses stem from the geochemical fingerprint that an animal’s environment leaves in its bones, teeth, and tissues.

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The importance of meat in human evolution:

Contrary to views that humans evolved largely as a herbivorous animal in a ‘garden of Eden’ type of environment, historical evidence indicates a very different reality, at least in the last four to five million years of evolutionary adaptation. It was in this time frame that the ancestral hominid line emerged from the receding forests to become bipedal, open grassland dwellers. This was likely accompanied by dietary changes and subsequent physiological and metabolic adaptations. The evolutionary pressure for some primates to undergo this habitat and subsequent diet change involving open grassland, foraging/scavenging, related directly to massive changes in global climatic conditions, primarily drier conditions followed by worldwide expansion of the biomass of temperate climate grasses at the expense of wetland forests, accompanied by a worldwide faunal change, including the spread of large grazing animals. Thus, the foods available to human ancestors in an open grassland environment were very different from those of the jungle/forest habitats that were home for many millions of years.

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Our early ancestors had diets that consisted mainly of low-nutrient plant material. This meant that they needed to spend significant amounts of time feeding in order to consume their energy requirements. The inclusion of meat in the diet was a turning point in human evolution. Eating meat provided our ancestors with more proteins and fats and higher energy levels. This allowed them to develop and sustain an active lifestyle and develop a larger brain.

When our ancestors included meat as a significant part of their diet, the effects were far reaching. These effects included:

  1. a reduction in tooth and jaw size, which is linked with a reduction in chewing.
  2. a decrease in the size of the intestinal tract and an increase in brain size.
  3. a reduction in the time needed for food gathering, leaving more time for learning and social activities.
  4. an ability to live in more varied environments than had previously been possible as herbivores. Non-seasonal animal food resources could now be utilised rather than having to rely on seasonal fruits, tubers and other plant foods with restricted ranges.

Herbivores require a large intestinal tract because vegetation is harder to digest than meat. When a greater proportion of meat was included in the diet, the digestive system was able to shrink in size and more energy became available to sustain a large brain. Homo ergaster was the first of our extinct relatives to have a thin waist and a small intestinal tract accompanied by a significantly larger brain.

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The lines of investigation used by anthropologists to deduce the evolutionary diet of our evolving hominid ancestors are numerous: (i) changes in cranio-dental features; (ii) fossil isotopic chemical tracer methods; (iii) comparative gut morphology of modern humans and other mammals; (iv) the energetic requirements of developing a large ratio of brain to body size; (v) optimal foraging theory; (vi) dietary patterns of surviving hunter-gatherer (HG) societies; and (vii) specific diet-related adaptations. Findings from each of these fields reveal a changing dietary pattern away from low-quality/highly fibrous, energy-poor plant stables to a growing dependence on more energy-rich animal foods, culminating in palaeolithic Homo sapiens being top-level carnivores.

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In a nutshell

  1. Human ancestral diets changed substantially approximately four to five million years ago with major climatic changes creating open grassland environments.
  2. We developed a larger brain balanced by a smaller, simpler gastrointestinal tract requiring higher-quality foods based around meat protein and fat.
  3. Anthropological evidence from cranio-dental features and fossil stable isotope analysis indicates a growing reliance on meat consumption during human evolution.
  4. Study of hunter-gatherer societies in recent times shows an extreme reliance on hunted and fished animal foods for survival.
  5. Optimal foraging theory shows that wild plant foods in general give an inadequate energy return for survival, whereas the top-ranking food items for energy return are large hunted animals.
  6. Numerous evolutionary adaptations in humans indicate high reliance on meat consumption, including poor taurine production, lack of ability to chain elongate plant fatty acids and the co-evolution of parasites related to dietary meat.

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Was cannibalism practiced?

Cannibalism is the act of a species consuming other members of its own species or kind. About 15 primate species, including chimps and modern humans, have been proven to have practiced or still practice cannibalism.

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The Importance of dietary carbohydrate in Human Evolution, a 2015 study:

Authors propose that plant foods containing high quantities of starch were essential for the evolution of the human phenotype during the Pleistocene. Although previous studies have highlighted a stone tool-mediated shift from primarily plant-based to primarily meat-based diets as critical in the development of the brain and other human traits, they argue that digestible carbohydrates were also necessary to accommodate the increased metabolic demands of a growing brain. Furthermore, they acknowledge the adaptive role cooking played in improving the digestibility and palatability of key carbohydrates. Authors provide evidence that cooked starch, a source of preformed glucose, greatly increased energy availability to human tissues with high glucose demands, such as the brain, red blood cells, and the developing fetus. They also highlight the auxiliary role copy number variation in the salivary amylase genes may have played in increasing the importance of starch in human evolution following the origins of cooking. Salivary amylases are largely ineffective on raw crystalline starch, but cooking substantially increases both their energy-yielding potential and glycemia.

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How do we know how they died?

The bones of some ancient individuals can tell us how their owners died. Some individuals had diseases that can be seen from the structure of their bones or teeth. Some had physical injuries that produce unique types of damage. Microscopes, X-rays, chemical analysis and other laboratory techniques help reveal their stories. A two-million-year old fossil Paranthropus skullcap (SK 54) from Swartkrans in South Africa has provided some interesting information about the death of one young individual. The skullcap has been pierced leaving two small, round holes. These holes have been perfectly matched to the canine teeth in the jaw of an ancient species of leopard. It seems that a leopard caught the adolescent and dragged its prey up into a tree to eat, just as modern leopards do today. The left-overs from this meal fell out of the tree and dropped into a cavity in the ground below. This cavity was part of a cave system that trapped the debris from many predators’ meals, the bones from which were later preserved as fossils.

The Taung Child (Australopithecus africanus) was only a tiny three-year-old when it was seized by an eagle 2.3 million years ago. We know an eagle or another bird of prey took this child because puncture marks and depression fractures to the skull are similar to those that occur on the prey of eagles today. Microscopic analysis supports this by showing scratches on the skull produced by clawed talons.

The Turkana Boy (Homo ergaster) lived in Africa about 1.5 million years ago. Although he died young, his bones show that he did not die from an attack by a predator because his nearly complete skeleton shows no damage from either predators or scavengers. Instead, his jaw shows that he had a diseased gum where a deciduous molar – one of his baby teeth – had been shed. An infection seems to have set in and he probably died of septicaemia (blood poisoning). Another individual who lived about 400,000 years ago probably died as a result of severe tooth decay and gum disease. The skull of this ancient human (Homo heidelbergensis), known as Kabwe or Broken Hill, had many large tooth cavities and abscesses which affected the jaw bone in which the teeth were embedded. This individual was unusual because ancient humans rarely showed such significant dental decay, probably because human diets were generally low in sugar until the beginnings of agriculture about 10,000 years ago.

The partial skeleton of woman known only as KNM-ER 1808 (Homo ergaster) was found in 1973. She died about 1.7 million years ago from a painful condition that may have been caused by vitamin A poisoning. This cause of death is suggested by the layer of abnormal bone which covered the bones in her arms and legs. This abnormal bone is similar to that found in modern humans with vitamin A poisoning. Excess vitamin A in the diet is toxic to our bodies and causes the tissues around the bone to tear, bleed and form huge clots. Abnormal bone tissue like that seen in KNM-ER 1808 then begins to grow. To have been poisoned by vitamin A, KNM-ER 1808’s diet must have included large quantities of foods high in this vitamin. Foods that have concentrated levels of vitamin A in them include honeybee broods (eggs, pupae and larvae) and the livers from carnivorous animals. Analysis of KNM-ER 1808’s teeth shows she had been a meat eater so it is possible that her poisoning resulted from eating too many livers taken from carnivorous animals.

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Origin and migration of humans:

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The idea that modern humans originated in Africa, with populations subsequently spreading outwards from there, has continued to gain support lately. But much of that support has come from analyses of genetic variation in people today, and from fossil and archaeological discoveries dated to within the past 120,000 years — after our species evolved. Hard evidence for the inferred African origin of modern humans has remained somewhat elusive, with relevant material being fragmentary, morphologically ambiguous or uncertainly dated. So the fossilized partial skulls from Ethiopia are probably some of the most significant discoveries of early Homo sapiens so far, owing to their completeness and well-established antiquity of about 160,000 years.

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The traditional human origin story maintains that modern humans, or homo sapiens, evolved in Africa and then migrated in a single wave to the Asian continent about 60,000 years ago. It’s better known as the “Out of Africa” model. Today, researchers are revising that narrative. According to a study published in Science, new discoveries over the last decade have shown that modern humans likely originated from several migrations from Africa that began as early as 120,000 years ago. Researchers have found fossils in southern and central China dating between 70,000 and 120,000 years ago or 120 ka (kilo annum). The original Out of Africa theory isn’t completely inaccurate. The early migrants were likely small groups of foragers. A later, major ‘Out of Africa’ event most likely occurred around 60 000 years ago or thereafter.

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There are two broad theories about the origins of H. sapiens. A few researchers still support a version of the ‘multiregional’ hypothesis, arguing that the anatomical features of modern humans arose in geographically widespread hominid populations throughout the Pleistocene epoch (which lasted from around 1.8 million to some 12,000 years ago). But most now espouse a version of the ‘out of Africa’ model, although there are differences of opinion over the complexity of the processes of origin and dispersal, and over the amount of mixing that might subsequently have occurred with archaic (non-modern) humans outside of Africa. Within Africa, uncertainties still surround the mode of modern human evolution — whether it proceeded in a gradual and steady manner or in fits and starts (punctuational evolution). Other questions concern the relationship between genetic, morphological and behavioural changes, and the precise region, or regions, of origin. For instance, possible early H. sapiens fossils, dating from about 260,000 to 130,000 years ago, are scattered across Africa at sites such as Florisbad (South Africa), Ngaloba (Tanzania), Eliye Springs and Guomde (Kenya), Omo Kibish (Ethiopia), Singa (Sudan) and Jebel Irhoud (Morocco). But the best dated of these finds, from Florisbad and Singa, are problematic because of incompleteness and, in the latter case, evidence of disease. Meanwhile, the more complete or diagnostically modern specimens suffer from chronological uncertainties. So the most securely dated and complete early fossils that unequivocally share an anatomical pattern with today’s H. sapiens are actually from Israel, rather than Africa. These are the partial skeletons from Skhul and Qafzeh, dating from around 115,000 years ago. Their presence in the Levant is usually explained by a range expansion from ancestral African populations, such as those sampled at Omo Kibish or Jebel Irhoud, around 125,000 years ago. The new cranial material from Herto, Ethiopia — described by White and colleagues — adds significantly to our understanding of early H. sapiens evolution in Africa. The fossils are complete enough to show a suite of modern human characters, and are well constrained by argon-isotope dating to about 160,000 years ago. Three individuals are represented by separate fossils: a nearly complete adult cranium (skull parts excluding the lower jaw), a less complete juvenile cranium, and some robust cranial fragments from another adult. All display evidence of human modification, such as cut marks, considered to represent mortuary practices rather than cannibalism. Associated layers of sediment produced evidence of the butchery of large mammals such as hippopotamuses and bovines, as well as assemblages of artefacts showing an interesting combination of Middle Stone Age and late Acheulean technology. The morphology of the most complete of these three fossils helps to clarify the pattern of early H. sapiens evolution in Africa, as it shows an interesting combination of features from archaic, early modern and recent humans. The cranium is very large, but once the size is standardized, it shares with ancient African crania a wide interorbital breadth (the distance between the orbits of the eyes), anteriorly placed teeth, and a short occipital (the bone at the rear of the braincase). It also has a wide upper face and moderately domed forehead, as do the Skhul and Qafzeh fossils. Its low nose and face and flat midface are more widely shared early H. sapiens features, whereas other characteristics, such as its globular braincase, are typically modern. In the angulation and transverse ridge of the occipital, there is also an intriguing resemblance to fossils from sites such as Elandsfontein (South Africa) and Broken Hill (Zambia) that are often assigned to H. heidelbergensis or H. rhodesiensis. This may provide a clue to the individual’s ancestors. But overall, the fossil seems closest in morphology to particular crania from Jebel Irhoud, Omo Kibish and Qafzeh.

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The figure above shows the geographical and temporal distribution of hominid populations, based on fossil finds, using different taxonomic schemes. The new finds from Herto represent early Homo sapiens. a, This reflects the view that both Neanderthals and modern humans derived from a widespread ancestral species called H. heidelbergensis.  b, However, evidence is growing that Neanderthal features have deep roots in Europe, so H. neanderthalensis might extend back over 400,000 years. The roots of H. sapiens might be similarly deep in Africa, but this figure represents the alternative view that the ancestor was a separate African species called H. rhodesiensis. Different views of early human evolution are also shown. Some workers prefer to lump the earlier records together and recognize only one widespread species, H. erectus (shown in a). Others recognize several species, with H. ergaster and H. antecessor (or H. mauritanicus) in the West, and H. erectus only in the Far East (shown in b).  What is shown in b is also shown in earlier paragraph of evolution of genus Homo.

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Out of Africa model:

The ‘Out of Africa’ model is currently the most widely favoured explanation accounting for the origins of modern humans. It suggests that modern humans originated in Africa within the last 200,000 years from a single group of ancestors. Modern humans continued to evolve in Africa and had spread to the Middle East by 100,000 years ago and possibly as early as 160,000 years ago. Modern humans only became well established elsewhere in the last 50,000 years. The ‘Out of Africa’ model has had a variety of names including:

  • ‘The Garden of Eden’ hypothesis
  • ‘Noah’s Ark’ hypothesis
  • ‘Out of Africa 2’ hypothesis, which distinguishes the earlier and later dispersals of humans out of Africa. In this case, ‘Out of Africa 1’ refers to the initial dispersal out of Africa by Homo ergaster, whereas ‘Out of Africa 2’ refers to the later dispersal out of Africa by modern humans.

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Single Origin (Out of Africa) versus Multiregional:

There are two main scientific theories about the biological development and migration patterns of modern humans: Single Origin (Out of Africa, Population Replacement) and Multiregional. The two main hypotheses agree that Homo erectus evolved in Africa and spread to the rest of the world around 1 – 2 million years ago; it is regarding our more recent history where they disagree.

  1. Single Origin claims that all ancestors of modern humans originated in Africa; they migrated outward and displaced other hominid populations throughout the world. Single Origin is dominant among scientists, although Multiregional has some support. Recent African origin proposes that modern humans evolved once in Africa between 100 – 200 thousand years ago and modern humans subsequently colonised the rest of the world without genetic mixing with archaic forms. It is supported by the majority of genetic evidence.
  2. Multiregional Continuity claims that our ancestors evolved continually in separate groups, but interbreeding between groups produced a unity of the human species across races. Multi-regional evolution suggests that modern humans evolved from archaic forms (such as Neanderthal and Homo erectus) concurrently in different regions of the world. It is supported by physical evidence, such as the continuation of morphological characteristics between archaic and modern humans.

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The replacement model of Christopher Stringer and Peter Andrews proposes that modern humans evolved from archaic humans 200,000-150,000 years ago only in Africa and then some of them migrated into the rest of the Old World replacing all of the Neandertals and other late archaic humans beginning around 60,000-40,000 years ago or somewhat earlier.   If this interpretation of the fossil record is correct, all people today share a relatively modern African ancestry.  All other lines of humans that had descended from Homo erectus presumably became extinct.  From this view, the regional anatomical differences that we now see among humans are recent developments–evolving mostly in the last 40,000 years.  This hypothesis is also referred to as the “out of Africa”, “Noah’s ark”, and “African replacement” model. The regional continuity model (or multiregional evolution model) advocated by Milford Wolpoff proposes that modern humans evolved more or less simultaneously in all major regions of the Old World from local archaic humans. For example, modern Chinese are seen as having evolved from Chinese archaic humans and ultimately from Chinese Homo erectus. This would mean that the Chinese and some other peoples in the Old World have great antiquity in place.  Supporters of this model believe that the ultimate common ancestor of all modern people was an early Homo erectus in Africa who lived at least 1.8 million years ago.  It is further suggested that since then there was sufficient gene flow between Europe, Africa, and Asia to prevent long-term reproductive isolation and the subsequent evolution of distinct regional species.  It is argued that intermittent contact between people of these distant areas would have kept the human line a single species at any one time.  However, regional varieties, or subspecies, of humans are expected to have existed.

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Replacement Model Arguments:

There are two sources of evidence supporting the replacement model–the fossil record and DNA.  So far, the earliest finds of modern Homo sapiens skeletons come from Africa.  They date to nearly 200,000 years ago on that continent.  They appear in Southwest Asia around 100,000 years ago and elsewhere in the Old World by 60,000-40,000 years ago.  Unless modern human remains dating to 200,000 years ago or earlier are found in Europe or East Asia, it would seem that the replacement model better explains the fossil data for those regions.  However, the DNA data supporting a replacement are more problematical.

Beginning in the 1980’s, Rebecca Cann, at the University of California, argued that the geographic region in which modern people have lived the longest should have the greatest amount of genetic diversity today.  Through comparisons of mitochondrial DNA sequences from living people throughout the world, she concluded that Africa has the greatest genetic diversity and, therefore, must be the homeland of all modern humans.  Assuming a specific, constant rate of mutation, she further concluded that the common ancestor of modern people was a woman living about 200,000 years ago in Africa.  This supposed predecessor was dubbed “mitochondrial Eve”.  More recent genetic research at the University of Chicago and Yale University lends support to the replacement model.  It has shown that variations in the DNA of the Y chromosome and chromosome 12 also have the greatest diversity among Africans today. All men today have inherited their Y chromosomes from a man who lived 140,000 years ago, probably in Africa. He has been named Y-chromosomal Adam. Studies of both the mitochondrial DNA (mtDNA) mismatch patterns in modern African populations and related mtDNA lineage-analysis patterns point to a major demographic expansion centered broadly within the time range from 80,000 to 60,000 B.P., probably deriving from a small geographical region of Africa.  Evidence from autosomal DNA also supports the recent African origin. Stone tools and other artifacts also support African origin.

Academics analysed the mitochondrial DNA (mtDNA) and Y chromosome DNA of Aboriginal Australians and Melanesians from New Guinea. This data was compared with the various DNA patterns associated with early humans. The research was an international effort, with researchers from Tartu in Estonia, Oxford, and Stanford in California all contributing key data and expertise. The results showed that both the Aborigines and Melanesians share the genetic features that have been linked to the exodus of modern humans from Africa 50,000 years ago. Until now, one of the main reasons for doubting the “Out Of Africa” theory was the existence of inconsistent evidence in Australia. The skeletal and tool remains that have been found there are strikingly different from those elsewhere on the “coastal expressway” – the route through South Asia taken by the early settlers.

John Relethford and other critics of the replacement model have pointed out that Africa could have had the greatest diversity in DNA simply because there were more people living there during the last several hundred thousand years.  This would leave open the possibility that Africa was not necessarily the only homeland of modern humans. Critics of the genetic argument for the replacement model also point out that the rate of mutation used for the “molecular clock” is not necessarily constant, which makes the 200,000 year date for “mitochondrial Eve” unreliable.  The rate of inheritable mutations for a species or a population can vary due to a number of factors including generation time, the efficiency of DNA repair within cells, ambient temperature, and varying amounts of natural environmental mutagens.  In addition, some kinds of DNA molecules are known to be more subject to mutation than others, resulting in faster mutation rates.  This seems to be the case with the Y chromosome in human males. Further criticism of the genetic argument for the replacement model has come from geneticists at Oxford University.  They found that the human betaglobin gene is widely distributed in Asia but not in Africa.  Since this gene is thought to have originated more than 200,000 years ago, it undercuts the claim that an African population of modern Homo sapiens replaced East Asian archaic humans less than 60,000 years ago.

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Evidence supporting the Out of Africa model:

  • the oldest known fossils of Homo sapiens are African
  • fossil evidence indicates that modern humans quickly replaced earlier humans in Europe and western Asia.
  • all living people show little genetic diversity. This is interpreted as being the result of a relatively recent replacement of earlier, more diverse populations.
  • a variety of different DNA studies on modern humans all suggest a recent common ancestry from a small gene pool. Most of these point to Africa as the origin of this population
  • DNA from contemporary humans can be used to produce maps of human movement throughout the world and show how long an indigenous population has lived in an area. These indicate modern human origins in Africa.
  • analysis of the Neanderthal genome and comparisons with modern humans does support the view that the vast majority of genes of non-Africans came with the spread of modern humans that originated in Africa and then spread throughout the world.

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Regional Continuity Model Arguments:

Fossil evidence also is used to support the regional continuity model.  Its advocates claim that there has been a continuity of some anatomical traits from archaic humans to modern humans in Europe and Asia.  In other words, the Asian and European physical characteristics have antiquity in these regions going back over 100,000 years.  They point to the fact that many Europeans have relatively heavy brow ridges and a high angle of their noses reminiscent of Neandertals.  Similarly, it is claimed that some Chinese facial characteristics can be seen in an Asian archaic human fossil from Jinniushan dating to 200,000 years ago.  Like Homo erectus, East Asians today commonly have shovel-shaped incisors while Africans and Europeans rarely do.  This supports the contention of direct genetic links between Asian Homo erectus and modern Asians.  Alan Thorne of the Australian National University believes that Australian aborigines share key skeletal and dental traits with pre-modern people who inhabited Indonesia at least 100,000 years ago.  The implication is that there was no replacement by modern humans from Africa 60,000-40,000 years ago.  However, the evidence does not rule out gene flow from African populations to Europe and Asia at that time and before.  David Frayer, of the University of Kansas, believes that a number of European fossils from the last 50,000 years have characteristics that are the result of archaic and modern humans interbreeding.  In 2000, the mitochondrial DNA (mtDNA) sequence of “Mungo Man 3” (LM3) of ancient Australia was published indicating that Mungo Man was an extinct subspecies that diverged before the most recent common ancestor of contemporary humans. The results, if correct, support the multiregional origin of modern humans hypothesis. This work was later questioned and explained by W. James Peacock, leader of the team who sequenced Mungo man’s ancient mtdna.

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Evidence supporting the Multiregional model:

  • there are similarities between some skull features found in modern humans and in ancient humans from the same regions.
  • some modern Asians have features similar to those of some ancient humans from China (in the Out of Africa model these ancient humans are known as Chinese Homo erectus).
  • some modern Australian Aboriginal people show similarities to some ancient humans from Indonesia (in the Out of Africa model these ancient humans are known as Indonesian Homo erectus)
  • some modern Europeans show similarities to ancient humans from Europe (in the Out of Africa model these ancient humans are known as the Neanderthals, or Homo neanderthalensis).
  • all living people show little genetic diversity. This is interpreted as being the result of continuous mixing of genes among regional populations.

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Assimilation Model:

It is apparent that both the complete replacement and the regional continuity models have difficulty accounting for all of the fossil and genetic data. What has emerged is a new hypothesis known as the assimilation (or partial replacement) model.  It takes a middle ground and incorporates both of the old models.  Gunter Brauer, of the University of Hamburg in Germany, proposes that the first modern humans did evolve in Africa, but when they migrated into other regions they did not simply replace existing human populations.  Rather, they interbred to a limited degree with late archaic humans resulting in hybrid populations.  In Europe, for instance, the first modern humans appear in the archaeological record rather suddenly around 45-40,000 years ago.  The abruptness of the appearance of these Cro-Magnon people could be explained by their migrating into the region from Africa via an eastern Mediterranean coastal route.  They apparently shared Europe with Neandertals for another 12,000 years or more.  During this long time period, it is argued that interbreeding occurred and that the partially hybridized predominantly Cro-Magnon population ultimately became modern Europeans.  In 2003, a discovery was made in a Romanian cave named Peştera cu Oase that supports this hypothesis.  It was a partial skeleton of a 15-16 year old male Homo sapiens who lived about 30,000 years ago or a bit earlier.  He had a mix of old and new anatomical features.  The skull had characteristics of both modern and archaic humans.  This could be explained as the result of interbreeding with Neandertals according to Erik Trinkaus of Washington University in St. Louis.  Alan Templeton, also of Washington University, reported that a computer-based analysis of 10 different human DNA sequences indicates that there has been interbreeding between people living in Asia, Europe, and Africa for at least 600,000 years. There’s also new evidence that modern humans interbred with Neanderthals as well as the more recently discovered relatives, the Denisovans, and other hominin groups, a sign that homo sapiens and other groups overlapped in Asia and interacted often.  This is consistent with the hypothesis that humans expanded again and again out of Africa and that these emigrants interbred with existing populations in Asia and Europe.  It is also possible that migrations were not only in one direction–people could have migrated into Africa as well.  If interbreeding occurred, it may have been a rare event.  This is supported by the fact that most skeletons of Neandertals and Cro-Magnon people do not show hybrid characteristics.

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Map of early human migrations:

Homo sapiens populations spread east to South Asia by 50,000 years ago, and on to Australia by 40,000 years ago, Homo sapiens for the first time colonizing territory never reached by Homo erectus. Europe was reached by Cro-Magnon some 40,000 years ago. East Asia (Korea, Japan) was reached by 30,000 years ago. It is disputed whether subsequent migration to North America took place around 30,000 years ago, or only considerably later, around 14,000 years ago.

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Agriculture and Migrations:

Since the evolution of H. erectus, migrations have been a fact of human existence, helping to spread genetic diversity as well as technological innovation. The most recent innovations have not been physical, but rather cultural. The Neolithic transition, about 10,000 years ago, involved the change from hunter-gatherer societies to agricultural ones based on cultivation of plants and domesticated animals. Evidence suggests this began in the Middle East and spread outward via migrations. Genetic studies suggest agriculture spread by the migration of farmers into hunter-gatherer societies. This would produce a genetic blurring as the farmers interbred with the indigenous peoples, a pattern supported by genetics. Most anthropologists agree that the New World was populated by a series of three migrations over the temporary land connection between Asia and North America. The immigrants spread southward, eventually reaching Tierra del Fuego in the southernmost part of South America.

Anthropological and linguistic studies find three groups of peoples:

  1. The Amerinds, who spread across North and South America
  2. The Na-Denes, who occupied the northwestern region of North America
  3. The Eskaleuts, Eskimo and Aleut peoples who live in the far north.

Mitochondrial DNA studies find four distinct groups descended from peoples of Siberia. Amerind mtDNA suggests two waves of migration (one perhaps as old as 21-42 thousand years ago). The genetic model confirms the accepted ideas about human migration into the Americas and suggests a possible fourth wave.

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Ancient DNA tells tales of humans’ migrant history:

Scientists once could reconstruct humanity’s distant past only from the mute testimony of ancient settlements, bones, and artifacts. No longer. Now there’s a powerful new approach for illuminating the world before the dawn of written history — reading the actual genetic code of our ancient ancestors. Two papers published in the journal Nature on February 21, 2018 show the number of ancient humans whose DNA has been analyzed and published to 1,336 individuals from up from just 10 in 2014. The new flood of genetic information represents a “coming of age” for the nascent field of ancient DNA, says lead author David Reich, a Howard Hughes Medical Institute investigator at Harvard Medical School — and it upends cherished archeological orthodoxy. “When we look at the data, we see surprises again and again and again,” says Reich. Together with his lab’s previous work and that of other pioneers of ancient DNA, the Big Picture message is that our prehistoric ancestors were not nearly as homebound as once thought. “There was a view that migration is a very rare process in human evolution,” Reich explains. Not so, says the ancient DNA. Actually, Reich says, “the orthodoxy — the assumption that present-day people are directly descended from the people who always lived in that same area — is wrong almost everywhere.” Instead, “the view that’s emerging — for which David is an eloquent advocate — is that human populations are moving and mixing all the time,” says John Novembre, a computational biologist at the University of Chicago.  The startling revelation from the ancient DNA was that the people moved, all the way to the Atlantic coast of Europe in the west to Mongolia in the east and India in the south. This vast migration helps explain the spread of Indo-European languages.

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People Today:

Are we genetically different from our Homo sapiens ancestors who lived 10-20,000 years ago?  The answer is almost certainly yes.  In fact, it is very likely that the rate of evolution for our species has continuously accelerated since the end of the last ice age, roughly 10,000 years ago.  This is mostly due to the fact that our human population has explosively grown and moved into new kinds of environments, including cities, where we have been subject to new natural selection pressures.  For instance, our larger and denser populations have made it far easier for contagious diseases, such as tuberculosis, small pox, the plague, and influenza to rapidly spread through communities and wreak havoc.  This has exerted strong selection for individuals who were fortunate to have immune systems that allowed them to survive.  There also has been a marked change in diet for most people since the end of the last ice age.  It is now less varied and predominantly vegetarian around the globe with a heavy dependence on foods made from cereal grains.  It is likely that the human species has been able to adapt to these and other new environmental pressures because it has acquired a steadily greater genetic diversity.  A larger population naturally has more mutations adding variation to its gene pool simply because there are more people.  This happens even if the mutation rate per person remains the same.  However, the mutation rate may have actually increased because we have been exposed to new kinds of man-made environmental pollution that can cause additional mutations. It is not clear what all of the consequences of the environmental and behavioral changes for humans have been.  However, it does appear that the average human body size has become somewhat shorter over the last 10,000 years, and we have acquired widespread immunity to the more severe effects of some diseases such as measles and influenza.

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Europe was the birthplace of mankind, not Africa, 2017 study:

The history of human evolution has been rewritten after scientists discovered that Europe was the birthplace of mankind, not Africa.  Currently, most experts believe that our human lineage split from apes around seven million years ago in central Africa, where hominids remained for the next five million years before venturing further afield.

But two fossils of an ape-like creature which had human-like teeth have been found in Bulgaria and Greece, dating to 7.2 million years ago. The discovery of the creature, named Graecopithecus freybergi, and nicknameded ‘El Graeco’ by scientists, proves our ancestors were already starting to evolve in Europe 200,000 years before the earliest African hominid. An international team of researchers say the findings entirely change the beginning of human history and place the last common ancestor of both chimpanzees and humans – the so-called Missing Link – in the Mediterranean region. At that time climate change had turned Eastern Europe into an open savannah which forced apes to find new food sources, sparking a shift towards bipedalism, the researchers believe. The team analysed the two known specimens of Graecopithecus freybergi: a lower jaw from Greece and an upper premolar tooth from Bulgaria. Using computer tomography, they were able to visualise the internal structures of the fossils and show that the roots of premolars are widely fused. While great apes typically have two or three separate and diverging roots, the roots of Graecopithecus converge and are partially fused – a feature that is characteristic of modern humans, early humans and several pre-humans. The lower jaw, has additional dental root features, suggesting that the species was a hominid. However some experts were more skeptical about the findings. Retired anthropologist and author Dr Peter Andrews, formerly at the Natural History Museum in London, said: “It is possible that the human lineage originated in Europe, but very substantial fossil evidence places the origin in Africa, including several partial skeletons and skulls. I would be hesitant about using a single character from an isolated fossil to set against the evidence from Africa.” All of this points to why the new claims about Graecopithecus need to be treated with a good deal of caution. First, there is only a single jaw and one isolated tooth to go on. Second, its human status is being judged from only a single feature, the configuration of the premolar tooth roots. We are open to the idea that early humans lived beyond Africa, but Graecopithecus falls well short of proving it.

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Discoveries in 2017 are changing the story of human evolution: Homo sapiens may have been around as long as 400,000 years, migrating out of Africa and having sex with Neanderthals and Denisovans. It seems now that Homo sapiens has been around for much longer than we thought, and that our ancestors were also clearly leaving Africa tens or even hundreds of thousands of years before the vaunted great exodus of 60,000 years ago. They were intermixing with other hominid species and, it seems, not all those “early waves” of people went extinct.

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Evidence of theory of evolution and natural selection:

In a broad sense, “evolution” refers simply to any heritable change in a population of organisms over time. More specifically, “evolution” may refer to Charles Darwin’s overall theory of evolution, which itself comprises two theories each addressing a different aspect of evolutionary change: The theory of descent with modification addresses the pattern of the change, while the theory of modification through natural selection addresses the process or mechanism of the change. The theory of descent with modification postulates that all organisms have descended from one or a few common ancestors through a continuous process of branching. The theory of natural selection offers one possible mechanism, natural selection, as the directing or creative force behind the perceived pattern of evolution.  Some people, emphasizing the division of evolutionary change into two types—macroevolution above the species level and microevolution within species—assert that the evidences of natural selection as the causal agent of evolutionary change are found only on the microevolutionary level. Others, perceiving the distinction between macro- and microevolution as an artificial construct, assert that natural selection is a single continuous process encompassing not only major changes above the species level but also change within species. Those holding this latter perspective tend to consider all evidence of evolution as support for the comprehensive theory of evolution that includes both the pattern of descent with modification and the mechanism of modification through natural selection.  Evidences from fossils, biogeography, homology, and genetics are among those used to support the theory of descent with modification. Evidences also are applied to support the theory of natural selection on the microevolutionary level. Evidence that would apply to natural selection at the macroevolutionary level, however, necessarily is based on extrapolation from evidence on the microevolutionary level.

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Evidence for the theory of descent with modification:

For the broad concept of evolution (“any heritable change in a population of organisms over time”), evidences of evolution are readily apparent on a microevolutionary level. These include observed changes in domestic crops (creating a variety of maize with greater resistance to disease), bacterial strains (development of strains with resistance to antibiotics), laboratory animals (structural changes in fruit flies), and flora and fauna in the wild (color change in particular populations of peppered moths and polyploidy in plants).

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Evidence for theory of natural selection:

On the microevolutionary level (change within species), there are evidences that natural selection does produce evolutionary change. For example, changes in gene frequencies can be observed in populations of fruit flies exposed to selective pressures in the laboratory environment. Likewise, systematic changes in various phenotypes within a species, such as color changes in moths, has been observed in field studies. However, evidence that natural selection is the directive force of change in terms of the origination of new designs (such as the development of feathers) or major transitions between higher taxa (such as the evolution of land-dwelling vertebrates from fish) is not observable. The conventional view of evolution is that macroevolution is simply microevolution continued on a larger scale, over large expanses of time. That is, if one observes a change in the frequencies of spots in guppies within 15 generations, as a result of selective pressures applied by the experimenter in the laboratory, then over millions of years one can get amphibians and reptiles evolving from fish due to natural selection. If a change in beak size of finches is seen in the wild in 30 years due to natural selection, then natural selection can result in new phyla if given eons of time. Indeed, the only concrete evidence for the theory of modification by natural selection—that natural selection is the causal agent of both microevolutionary and macroevolutionary change—comes from microevolutionary evidences, which are then extrapolated to macroevolution.

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The following are evidences of natural selection, albeit at the microevolutionary level:

  1. Laboratory evidences of natural selection:

In the laboratory, biologists have demonstrated natural selection on the microevolutionary level involving organisms with short lifecycles, such as fruit flies, guppies, and bacteria, which allow testing over many generations.

Endler (1980) set up populations of guppies (Poecilia reticulata) and their predators in artificial ponds in the laboratory, with the ponds varying in terms of the coarseness of the bottom gravel. Guppies have diverse markings (spots) that are heritable variations and differ from individual to individual. Within 15 generations in this experimental setup, the guppy populations in the ponds had changed according to whether they were exposed to coarse gravel or fine gravel. The end result was that there was a greater proportion of organisms with those markings that allowed the guppies to better blend in with their particular environment, and presumably better avoid being seen and eaten by predators. When predators were removed from the experimental setup, the populations changed such that the spots on the guppies stood out more in their environment, likely to attract mates, in a case of sexual selection.

Likewise, bacteria grown in a Petri dish can be given an antibiotic, such as penicillin, that is just strong enough to destroy most, but not all, of the population. If repeated applications are used after each population returns to normal size, eventually a strain of bacteria with antibiotic resistance may be developed. This more recent population has a different allele frequency than the original population, as a result of selection for those bacteria that have a genetic makeup consistent with antibiotic resistance. Recently, several new strains of MRSA have emerged that are resistant to vancomycin and teicoplanin. The appearance of vancomycin resistant Staphlococcus aureus, and the danger it poses to hospital patients is considered a direct result of evolution through natural selection. This exemplifies a situation where medical researchers continue to develop new antibiotics that can kill the bacteria, and this leads to resistance to the new antibiotics.

  1. A similar situation occurs with pesticide resistance in plants and insects. The appearance of DDT resistance in various forms of Anopheles mosquitoes, and the appearance of myxomatosis resistance in breeding rabbit populations in Australia are all considered similar evidence of the existence of evolution in situations of evolutionary selection pressure in species in which generations occur rapidly.
  2. Before the industrial revolution in Britain, most peppered moths were of the pale variety. This meant that they were camouflaged against the pale birch trees that they rest on. Moths with a mutant black colouring were easily spotted and eaten by birds. This gave the white variety an advantage, and they were more likely to survive to reproduce. Airborne pollution in industrial areas blackened the birch tree bark with soot. This meant that the mutant black moths were now camouflaged, while the white variety became more vulnerable to predators. This gave the black variety an advantage, and they were more likely to survive and reproduce. Over time, the black peppered moths became far more numerous in urban areas than the pale variety.
  3. Artificial selection:

Analogously to natural selection, for thousands of years, humans have artificially manipulated changes within species through artificial selection. By selecting for preferred characteristics in cattle, horses, grains, and so forth, various breeds of animals and varieties of plants have been produced that are different often in significant respects from their ancestors.

  1. Evidence from studies of complex iteration:

Computer science allows the iteration of self-changing complex systems to be studied, allowing a mathematical approach to understanding the nature of the processes behind evolution. Based on human concepts, such computer programs have provided theoretical evidence for the possibility of natural selection directing macroevolutionary changes and insights into possible hidden causes of known evolutionary events (Adami et al. 2000; Earl and Deem 2004; Stemmer 1994).

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Scientific evidence of human evolution:

The evidence on which scientific accounts of human evolution are based comes from many fields of natural science. The main source of knowledge about the evolutionary process has traditionally been the fossil record, but since the development of genetics beginning in the 1970s, DNA analysis has come to occupy a place of comparable importance. The studies of ontogeny, phylogeny and especially evolutionary developmental biology of both vertebrates and invertebrates offer considerable insight into the evolution of all life, including how humans evolved. The specific study of the origin and life of humans is anthropology, particularly paleoanthropology which focuses on the study of human prehistory. Scientists have discovered a wealth of evidence concerning human evolution, and this evidence comes in many forms. Fossils provide solid evidence that organisms from the past are not the same as those found today; fossils show a progression of evolution. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. This approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years. Thousands of human fossils enable researchers and students to study the changes that occurred in brain and body size, locomotion, diet, and other aspects regarding the way of life of early human species over the past 6 million years. Millions of stone tools, figurines and paintings, footprints, and other traces of human behavior in the prehistoric record tell about where and how early humans lived and when certain technological innovations were invented. Study of human genetics show how closely related we are to other primates – in fact, how connected we are with all other organisms – and can indicate the prehistoric migrations of our species, Homo sapiens, all over the world. Advances in the dating of fossils and artifacts help determine the age of those remains, which contributes to the big picture of when different milestones in becoming human evolved.

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Researchers claim that the theory of evolution has been supported by four primary sources that serve as evidence (Zimmer, 2002; Allenand Briggs, 1989):

  • Anatomy. Species may share similar physical features because the feature was present in a common ancestor (homologous structures).
  • Molecular biology. DNA and the genetic code reflect the shared ancestry of life. DNA comparisons can show how related species are.
  • Biogeography. The global distribution of organisms and the unique features of island species reflect evolution and geological change.
  • Fossils. Fossils document the existence of now-extinct past species that are related to present-day species.

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Anatomy and embryology:

Homology means correspondence of structures in two life forms with a common evolutionary origin, such as flippers and hands.

Analogy means the relationship between characteristics that are apparently similar but did not develop from the same structure.

Homologous features:

If two or more species share a unique physical feature, such as a complex bone structure or a body plan, they may all have inherited this feature from a common ancestor. Physical features shared due to evolutionary history (a common ancestor) are said to be homologous. To give one classic example, the forelimbs of whales, humans, birds, and dogs look pretty different on the outside. That’s because they’re adapted to function in different environments. However, if you look at the bone structure of the forelimbs, you’ll find that the pattern of bones is very similar across species. It’s unlikely that such similar structures would have evolved independently in each species, and more likely that the basic layout of bones was already present in a common ancestor of whales, humans, dogs, and birds.

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Figure above shows Homology in the forelimbs of vertebrates: The principle of homology illustrated by the adaptive radiation of the forelimb of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched. In genetics, homology is measured by comparing protein or DNA sequences. Homologous gene sequences share a high similarity, supporting the hypothesis that they share a common ancestor.

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Sometimes, organisms have structures that serve no apparent function but are homologous to useful structures in other organisms. These reduced or nonfunctional structures, which appear to be evolutionary “leftovers,” are called vestigial structures. Examples of vestigial structures include the tailbone of humans (a vestigial tail), the hind leg bones of whales, and the underdeveloped legs found in some snakes. The small leg-like structures of some snakes species, like the Boa constrictor, are vestigial structures. These remnant features serve no present purpose in snakes, but did serve a purpose in the snakes’ tetrapod ancestor (which walked on four limbs). The human vermiform appendix, an appendage of the cecum (the ascending colon) has long been claimed by evolutionary biologists as an example of a vestigial organ. It has been compared with the rabbit’s appendix, which is large and apparently functional as an aid in digesting cellulose.

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Analogous features:

To make things a little more interesting and complicated, not all physical features that look alike are marks of common ancestry. Instead, some physical similarities are analogous: they evolved independently in different organisms because the organisms lived in similar environments or experienced similar selective pressures. This process is called convergent evolution. (To converge means to come together, like two lines meeting at a point.) For example, two distantly related species that live in the Arctic, the arctic fox and the ptarmigan (a bird), both undergo seasonal changes of color from dark to snowy white. This shared feature doesn’t reflect common ancestry – i.e., it’s unlikely that the last common ancestor of the fox and ptarmigan changed color with the seasons.  Instead, this feature was favored separately in both species due to similar selective pressures. That is, the genetically determined ability to switch to light coloration in winter helped both foxes and ptarmigans survive and reproduce in a place with snowy winters and sharp-eyed predators.

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Evidence from embryology:

The field of embryology has long been claimed as a source of evidence supporting descent with modification. The assertion has been that the embryos of related animals are often quite similar to each other, often much more similar than the adult forms, and hence the embryos provide evidence of their descent from common ancestors. For example, it is held that the development of the human embryo correlates closely with comparable stages of other kinds of vertebrates (fish, salamander, tortoise, chicken, pig, cow, and rabbit). Furthermore, it is asserted that mammals such as cows and rabbits are more similar in embryological development than with alligators. The drawings of early vertebrate embryos by Ernst Haeckel have often been offered as proof of these presumed correlations even though the accuracy of those same drawings has been widely refuted (Gilbert 2006). Some homologous structures can be seen only in embryos. For instance, all vertebrate embryos (including humans) have gill slits and a tail during early development. The developmental patterns of these species become more different later on (which is why your embryonic tail is now your tailbone, and your gill slits have turned into your jaw and inner ear). Homologous embryonic structures reflect that the developmental programs of vertebrates are variations on a similar plan that existed in their last common ancestor.

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Biogeography:

Biologists have discovered many puzzling facts about the presence of certain species on various continents and islands (biogeography). The geographic distribution of plants and animals offers another commonly cited evidence for evolution (common descent). The fauna on Australia, with its large marsupials, is very different from that of the other continents. The fauna on Africa and South America are very different, but the fauna of Europe and North America, which were connected more recently, are similar. There are few mammals on oceanic islands. These findings support the theory of descent with modification, which holds that the present distribution of flora and fauna would be related to their common origins and subsequent distribution. The longer the separation of continents, as with Australia’s long isolation, the greater the expected divergence is.

Evidence for migration and isolation:

Camels and their relatives, the llamas, are found on two continents, with true camels in Asia and Africa, and llamas in South America (Mayr 2001). There are no camels in North America. Based on descent with modification, it would be expected that camels once existed in North America but became extinct. Indeed, there was the discovery of a large fossil fauna of Tertiary camels in North America (Mayr 2001). One proposal for the fossil record for the camel is that camels started in North America, from which they migrated across the Bering Strait into Asia and hence to Africa, and through the Isthmus of Panama into South America. Once isolated, they evolved along their own lines, producing the modern camel in Asia and Africa, the llama in South America, and becoming extinct in North America.

Continental drift:

The same kinds of fossils are found from areas known to have been adjacent to one another in the past, but which, through the process of continental drift, are now in widely divergent geographic locations. For example, fossils of the same types of ancient amphibians, arthropods, and ferns are found in South America, Africa, India, Australia, and Antarctica, which can be dated to the Paleozoic Era, at which time these regions were united as a single landmass called Gondwana. Sometimes the descendants of these organisms can be identified and show unmistakable similarity to each other, even though they now inhabit very different regions and climates.

Oceanic island distribution:

Most small isolated islands only have native species that could have arrived by air or water: Birds, insects, and turtles. The few large mammals present today were brought by human settlers in boats. Plant life on remote and recent volcanic islands like Hawaii could have arrived as airborne spores or as seeds in the droppings of birds. After the explosion of Krakatoa a century ago and the emergence of a steaming; in lifeless remnant island called Anak Krakatoa (child of Krakatoa), plants arrived within months and within a year there were moths and spiders that had arrived by air. Scarcely more than a century later the island has nearly completely recovered—to the extent that it is now difficult to distinguish the island ecologically from others nearby that have been there for millions of years.

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Evidence from biochemistry and molecular biology:

In Darwin’s day, the evidence of shared traits was based solely on visible observation of morphologic similarities, such as the fact that all birds—even those which do not fly—have wings. Today, the theory of common descent is supported by genetic similarities. For example, every living cell makes use of nucleic acids as its genetic material, and uses the same twenty amino acids as the building blocks for proteins. All organisms use the same genetic code (with some extremely rare and minor deviations) to specify the nucleic acid sequences that form proteins. The code used to translate nucleotide sequences into amino acid sequences is essentially the same in all organisms. Moreover, proteins in all organisms are invariably composed of the same set of 20 amino acids. This unity of composition and function is a powerful argument in favor of the common descent of the most diverse organisms. The proteomic evidence also supports the universal ancestry of life. Vital proteins, such as the ribosome, DNA polymerase, and RNA polymerase, are found in everything from the most primitive bacteria to the most complex mammals. The core part of the protein is conserved across all lineages of life, serving similar functions. Higher organisms have evolved additional protein subunits, largely affecting the regulation and protein-protein interaction of the core. Other overarching similarities between all lineages of extant organisms, such as DNA, RNA, amino acids, and the lipid bilayer, give support to the theory of common descent. The chirality of DNA, RNA, and amino acids is conserved across all known life. As there is no functional advantage to right- or left-handed molecular chirality, the simplest hypothesis is that the choice was made randomly by early organisms and passed on to all extant life through common descent.

Similarly, the metabolism of very different organisms is based on the same biochemistry. For example, the protein cytochrome c, which is needed for aerobic respiration, is universally shared in aerobic organisms, suggesting a common ancestor that used this protein. There are also variations in the amino acid sequence of cytochrome c, with the more similar molecules found in organisms that appear more related (monkeys and cattle) than between those that seem less related (monkeys and fish). The cytochrome c of chimpanzees is the same as that of humans, but very different from that of bread mold. Similar results have been found with blood proteins. Other uniformity is seen in the universality of mitosis in all cellular organisms, the similarity of meiosis in all sexually reproducing organisms, the use of ATP by all organisms for energy transfer, and the fact that almost all plants use the same chlorophyll molecule for photosynthesis.

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The unifying principle of common descent that emerges from all the foregoing lines of evidence is being reinforced by the discoveries of modern biochemistry and molecular biology. In 1959, scientists at Cambridge University in the United Kingdom determined the three-dimensional structures of two proteins that are found in almost every multicelled animal: hemoglobin and myoglobin. Hemoglobin is the protein that carries oxygen in the blood. Myoglobin receives oxygen from hemoglobin and stores it in the tissues until needed. During the next two decades, myoglobin and hemoglobin sequences were determined for dozens of mammals, birds, reptiles, amphibians, fish, worms, and molluscs. All of these sequences were so obviously related that they could be compared with confidence with the three-dimensional structures of two selected standards—whale myoglobin and horse hemoglobin. Even more significantly, the differences between sequences from different organisms could be used to construct a family tree of hemoglobin and myoglobin variation among organisms. This tree agreed completely with observations derived from paleontology and anatomy about the common descent of the corresponding organisms.

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Figure above shows that species that diverged long time ago have more differences in their corresponding proteins, reflecting changes in the amino acids over time. Proteins evolve at different rates depending on the constraints imposed by their functions. Cytochrome c, a protein involved in energy transfer, is tightly constrained and changes slowly. Fibrinopeptides, which are involved in blood clotting, are much less constrained, with hemoglobin an intermediate case. The estimates for times of divergence shown here are based on 1971 data and have changed slightly since then.

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The evidence for evolution from molecular biology is overwhelming and is growing quickly. In some cases, this molecular evidence makes it possible to go beyond the paleontological evidence. For example, it has long been postulated that whales descended from land mammals that had returned to the sea. From anatomical and paleontological evidence, the whales’ closest living land relatives seemed to be the even-toed hoofed mammals (modem cattle, sheep, camels, goats, etc.). Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and have suggested that the closest land-bound living relative of whales may be the hippopotamus. In this case, molecular biology has augmented the fossil record.

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Archaeological Evidence:

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Archaeological data provides an essential contribution to the study of human evolution. Primary archaeological datasets are varied and include stone tools, butchered animal remains, modified organic materials, structural remains and the traces of early art.  From these sources researchers are able to develop robust models of past human behaviour and examine variation across the globe within a timeframe which now exceeds 2.6 million years. Archaeological excavations also provide the best source for the recovery of high quality scientific data relating to ancient human anatomy, associated environmental evidence, and indications of dating. Consequently Palaeolithic field archaeology, with its distinctive approach to geological and sedimentary context and detailed recording methods capable of answering complex taphonomic questions, can be considered a specialised sub-discipline of wider archaeological fieldwork.

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Tools also provide evidence for human evolution. Primitive tools (flint hand axes) have been found in remains from the Palaeolithic Age (10,000 to 2.5 million years ago). More advanced tools (arrowheads) have been found from the Mesolithic Age (6,000 to 10,000 years ago), and even more advanced tools have been found from the Neolithic Age (4,000 to 6,000 years ago). Analysis of prehistoric stone artifacts from Lower Pleistocene sites at Koobi Fora, Kenya, and Middle Pleistocene horizons at Ambrona, Spain reveals a preferential, clockwise rotation of stone cores during flaking. Experimental studies of early stone artifact manufacture show that this non-random pattern is consistent with that produced by right-handed toolmakers. This suggests that there was a genetic basis for right-handedness by 1.4 to 1.9 million years ago, and that there may have already been a profound lateralization in the hominid brain with the two hemispheres becoming more specialized for different functions.

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What caused dramatic expansion in African populations ≈60,000–80,000 B.P.?

It is here that recent archaeological research in southern and central Africa becomes central to the interpretation of the demographic data. The most relevant evidence at present comes from a number of sites located close to the southern tip of Africa in Cape Province, most notably from Blombos Cave and Klasies River on the southern coast and those of Boomplaas Cave and Diepkloof, further to the north and west. These are backed up by a number of rather less well documented sites in eastern and central Africa. The general time range of these sites is that of the African Middle Stone Age (MSA) extending from ≈250,000 to 40,000 B.P., and coinciding broadly with the Middle Palaeolithic (or Mousterian) periods in Europe and Asia. But the relevant evidence from the so-called “Still Bay” levels in the Blombos Cave and the ensuing “Howiesons Poort” levels at Klasies River, Boomplaas, and Diepkloof, can be dated specifically to the later stages of the MSA, between ca. 75,000 and 55,000 B.P. Although the archaeological assemblages from these sites have traditionally been attributed to the MSA, they reveal a number of radical technological and cultural features that collectively contrast sharply with those of the earlier African MSA sites, and which show many resemblances to those that appear in Europe and western Asia with the arrival of the first anatomically and genetically modern populations at ≈45,000–50,000 B.P., the period of the so-called “Upper Palaeolithic revolution”. These assemblages include, for example, new patterns of blade technology, produced by means of “soft hammer” techniques of flaking; new forms of both specialized skin working tools (end-scrapers) and tools for the controlled shaping of bone and wooden artefacts (so-called burin forms); a range of extensively shaped bone tools, apparently used as both tips of throwing spears and sharply pointed awls for skin working; new forms of carefully shaped stone inserts, probably used as tips and barbs of either hafted throwing spears or conceivably wooden arrows; large numbers of perforated estuarine shells, evidently used as personal ornaments of some kind; and large quantities of imported red ochre, including two pieces from the Blombos cave with carefully incised and relatively complex geometrical designs on their surfaces. These designs represent the earliest unambiguous forms of abstract “art” so far recorded. Equally significant in these sites is the evidence for the large-scale distribution or exchange of both high-quality stone for tool production and the recently discovered shell beads from the Blombos cave, in both cases either transported or traded over distances of at least 20–30 kms. All of these features show a striking resemblance to those which characterize fully modern or “Upper Palaeolithic” cultures in Europe and western Asia, which first appeared with the initial arrival of anatomically and behaviorally modern populations at ≈45,000–50,000 B.P., i.e., some 20,000 years later than their appearance in the African sites. As Henshilwood has recently commented, the combination of these behavioral innovations in the Still Bay and succeeding Howiesons Poort levels at these South African sites seems to reflect “a dynamic period of diverse technological behavior not previously seen in the African Middle Stone Age.”

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Many behaviors that are usually attributed to modern people have left traces in the archaeological record of Africa from about 200 to 100 ka. These innovations appeared in the following order: (1) shellfishing; (2) fine stone blades, grindstones, and ochre use; (3) stone points; (4) long-distance exchange of material; (5) fishing, bone tools, barbed points, mining, and etched items to record information; (6) microlithic blades and bead ornaments; and (7) images (McBrearty and Brooks, 2000; Marean et al., 2007).

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Fossil evidence:

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The primary resource for detailing the path of human evolution will always be fossil specimens. Certainly, the trove of fossils from Africa and Eurasia indicates that, unlike today, more than one species of our family has lived at the same time for most of human history. The nature of specific fossil specimens and species can be accurately described, as can the location where they were found and the period of time when they lived; but questions of how species lived and why they might have either died out or evolved into other species can only be addressed by formulating scenarios, albeit scientifically informed ones. These scenarios are based on contextual information gleaned from localities where the fossils were collected. In devising such scenarios and filling in the human family bush, researchers must consult a large and diverse array of fossils, and they must also employ refined excavation methods and records, geochemical dating techniques, and data from other specialized fields such as genetics, ecology and paleoecology, and ethology (animal behaviour)—in short, all the tools of the multidisciplinary science of paleoanthropology.

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Today, many of the gaps in the paleontological record have been filled by the research of paleontologists. Hundreds of thousands of fossil organisms, found in well-dated rock sequences, represent successions of forms through time and manifest many evolutionary transitions.  Microbial life of the simplest type was already in existence 3.5 billion years ago. The oldest evidence of more complex organisms (that is, eukaryotic cells, which are more complex than bacteria) has been discovered in fossils sealed in rocks approximately 2 billion years old. Multicellular organisms, which are the familiar fungi, plants, and animals, have been found only in younger geological strata. The following list presents the order in which increasingly complex forms of life appeared:

Life Form Millions of Years Since First Known Appearance (Approximate)
Microbial (prokaryotic cells) 3,500
Complex (eukaryotic cells) 2,000
First multicellular animals 670
Shell-bearing animals 540
Vertebrates (simple fishes) 490
Amphibians 350
Reptiles 310
Mammals 200
Nonhuman primates 60
Earliest apes 25
Australopithecine ancestors of humans 5
Modern humans 0.15 (150,000 years)

So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. Actually, nearly all fossils can be regarded as intermediates in some sense; they are life forms that come between the forms that preceded them and those that followed. The fossil record thus provides consistent evidence of systematic change through time—of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eukaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found.

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Fossils are important because they give direct evidence of the type of animals and plants that existed at a certain geological age. These records show that the different groups of organisms arose at different times on earth. For example, earliest fossils are of Monera, followed by protoctista and then fungi. Plants and animals appeared later. Even among the vertebrates the oldest fossils are those of the fishes, followed by amphibians and progressively mammals are the latest organisms to appear on earth. By comparing fossils of different organisms, it is possible to tell the phylogenetic relationships between organisms. Fossil records also show gradual increase in complexity of organisms over time. Older (lower) rock strata contain fossils showing simple structures while younger (upper) rock strata contain fossils showing more complex structures. Some fossil records have been used to reconstruct an almost complete evolutionary history of development of certain organisms. For instance, human fossils show progressive increase in skull sizes to the present age while evolutionary stages of the horse have been reconstructed on the basis of increased complexity of fossil limbs.  The age of recent fossils can be determined through radioactive dating using carbon– 14 while that of very old fossils is determined by determining the age of the rocks where the fossils are found using potassium – argon method.

However, use of fossil records in retracing evolutionary history of all present–day organisms has some limitations in that:

(i) There are several missing fossil records (missing links), due to decomposition of some part(s) or whole organisms, being scavenged upon, unavailability of suitable conditions for fossilization and only a few have been discovered.

(ii) Distortion of parts during sedimentation – which may give wrong impression of structures.

(iii) Destruction of fossils by geological activities e.g. earthquakes, faulting, uplifting and mass wasting.

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The fossil record can be used as evidence of evolution in countless ways.  At the most fundamental level it absolutely disproves the “recent (6,000 yr old) Creation theory”. Using radiometric dating with carbon 14, wooden artifacts are 20,000 and 30,000 years old together with the clothing and bones of the people who used them, that disproves the Creationism that puts Earth’s origin at 6,000 years ago. The fossil record then, relying on geological features such as uplift from earthquakes, the creation and degradation of mountain ranges, eons of accumulation of silt and the remains of  calciferous marine animals in their layers, enable us to go back hundreds of thousands and millions of years. Regardless of which science one is reviewing, whether geology, zoology, botany, anthropology, marine biology, the   progressively older the Earth strata are which are examined, the more primitive anatomically are the fossil specimens extracted from them.  Today we have animal species which have scales, fur, feathers, hair, bald skin or a mere cell membrane. The fossil record shows that 100 million years ago all animal species had only a cell membrane, scales, or bald skin. The fossil record shows that feathers evolved from scales.  Fur or length-specific hair by species covering most of the body came later, and more sparsely as isolated hairs with indeterminate growth evolved later still. Probably most important as far as the process of evolution is concerned, in relation to the fossil record, the latter indicates the oldest of all life on Earth was entirely bound in the seas. There were millions of years when the seas teemed with life, and dry land had not even appeared yet.

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Map of Africa showing the locations where key hominin species have been found:

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The pattern and process of human evolution can be described on the basis of a combination of comparative anatomy, the fossil record, and primate and human genetics (Kimbel and Martin, 1993). Comparative anatomy, even in Darwin’s time, indicated a close relationship between humans and African apes (Huxley, 1863), and this has been confirmed by comparative genetic analyses. Although the branching order of the ape family tree—gibbons, orangutans, gorillas, chimpanzees, humans—is firmly established, the dates of these branching splits are less certain (Kumar et al., 2005). The earliest fossils of the human lineage, after the split from the common ancestor of the chimpanzees, are fragmentary and the dates of some remain imprecise. A distorted cranium from Chad, Sahelanthropus tchadensis, has a reduced snout compared with apes, and skull characteristics that are sometimes taken to indicate bipedality (Brunet et al., 2002; Zollikofer et al., 2005). The site from which this specimen comes (Koro Toro) has recently been dated to between 6.8 and 7.2 Ma (Lebatard et al., 2008), and this estimate is consistent with the faunal evidence. Other early fossils from Kenya (Orrorin tugenensis; Senut et al., 2001) consist of fragmentary jaws and limb bones with dates of 5.7 to 6.0 Ma. Although there is debate about the exact relationship between O. tugenensis and later hominins, recent anatomical analyses of the skeleton (Richmond and Jungers, 2008) indicate that this species was habitually bipedal—a uniquely hominin trait. So by 6 Ma, our earliest ancestors had split from the chimpanzee lineage and become adapted to bipedal locomotion, which is the major difference that separates us from great apes.

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The fossil record of hominins between 6 and 3 Ma is patchy, but samples from Ethiopia, Kenya, Tanzania, and Chad record several bipedal hominins that have been placed in the genera Ardipithecus and Australopithecus. The early part of this hominin record (5.8 to 4.4 Ma) is represented by Ardipithecus, which had acquired some features seen in later Australopithecus, but which still exhibited primitive traits seen in African great apes (White et al., 1994, 1995, 2009 and associated articles).The species in the genus Australopithecus all have larger molar and premolar teeth and thicker enamel than their predecessors (Ward et al., 1999, 2001; White et al., 2006), and gradual change from A. anamensis to A. afarensis has been documented (Kimbel et al., 2006). Although their food processing anatomy differed, this lineage of bipedal hominins had brain to body mass ratios that are about the same as those of extant great apes. Their limb proportions differed from those of both chimpanzees and humans, and their pelvic and hip structure suggests a somewhat different mode of bipedal locomotion from that of our own genus Homo. Confirmation of bipedal locomotion comes from fossilized footprints at Laetoli in Tanzania (Leakey and Hay, 1979). Australopithecus species exhibited differences in body size and canine dimensions between males and females (i.e., sexual dimorphism). A. afarensis is well known from cranial and postcranial parts and includes the famous partial skeleton ”Lucy” from ~3.2 Ma. A related hominin—A. africanus—is well known but poorly dated from South African cave sites. One individual is of a nearly complete skeleton (Clarke, 1998; 2002), which promises to deliver much important information about this southern form. The youngest member of this genus, A. garhi, was recovered from 2.5-Ma deposits in Ethiopia (Asfaw et al., 1999), but little is known about it except that the trend throughout this lineage to larger jaws and teeth continued.

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Extremely large-toothed hominins appear in the record around 2.7 Ma. These are sometimes placed in Australopithecus but are more commonly assigned to their own genus, Paranthropus. These “robust” creatures, so-called because of their massively sized jaws and teeth, may be direct lineal descendents of A. afarensis. The earliest species from East Africa is P. aethiopicus, known only from a single cranium and other isolated skeletal parts. This species evolved into P. boisei, and fossils of this younger species are relatively common in East Africa (Constantino and Wood, 2007). A similar species, P. robustus, is found in cave sites in South Africa; these fossils are also found with bone fragments that were used to dig both tubers and termites (Backwell and D’Errico, 2001; Pickering et al., 2004). Although we have only discovered limited numbers of skeletal bones of these robust-jawed hominins, they seem to have been very similar to the earlier Australopithecus in their postcranial adaptations (the skeletal features aside from the skull, jaw, and teeth). It is likely that the larger jaws and teeth were used for chewing very hard foodstuffs. Paranthropus appears to have become extinct at about 1.2 Ma or shortly after, at the same time that several other African mammal species became extinct. Although there are many characteristics and capabilities that remain unknown, one thing is clear; Paranthropus existed at the same time and in the same areas as the earliest members of our own genus, Homo. Their co-occurrence is the firmest evidence for different species of hominins existing together.

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Behavioral evidence for the existence of our own genus, in the form of stone tools, predates any Homo fossils so far discovered, and although stone tools are commonly associated with the genus Homo throughout its existence it is not possible to be completely certain that Paranthropus did not make all or some of the earliest tools. Stone tools referred to as Oldowan technology, as old as 2.6 Ma, have been found in Ethiopia (Semaw et al., 2003). The earliest definite Homo fossil is a 2.3-Ma maxilla (upper jaw) from an Oldowan archaeological site at Hadar, Ethiopia (Kimbel et al., 1996), which shows a steeper facial profile and a broader palate than Australopithecus species. By about 2.0 Ma, fossils of early Homo and sites with animal bones and stone tools are relatively common. However, it is important to emphasize that although these hominins have been assigned to the genus Homo, this does not imply that they were very much like modern humans in anatomy and behavior. Consequently, we should be wary of attributing any particular human behavior or physiology to early Homo without strong evidence. We do not know which particular Australopithecus species gave rise to Homo, although there have been suggestions that A. garhi was the precursor species (Asfaw et al., 1999).

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KNM-ER 1813, Homo habilis

This fossil is discovered by Kamoya Kimeu in 1973 at Koobi Fora in Kenya (Leakey 1974). Estimated age is 1.8-1.9 million years. The brain size is 510 cc, which is very small for habilis, but the fossil is an adult specimen, probably of a female. Apart from its extremely small size, ER 1813 is surprisingly modern, with a rounded skull, no sagittal crest, modest eyebrow ridges, and a small amount of nasal prominence.

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The remains of Homo habilis are known from East Africa (Tobias, 1991; Wood, 1991), and possibly also from South Africa (Grine et al., 1993); this species is either very variable in cranial capacity and palate shape, or there are two species present. In general, this species has a mixture of primitive features as well as some that foreshadow those of the later H. erectus. Sexual dimorphism in body size was strong, like that of the preceding Australopithecus species. The appearance of early Homo erectus at about 1.9 Ma is marked by changes in the limb skeleton that make it nearly indistinguishable from that of modern humans; these changes have been associated with the capacity for long-distance running (Bramble and Lieberman, 2004). This species is the first hominin to disperse out of Africa. Dispersal of H. erectus to present-day Georgia, where it is found at Dmanisi, apparently took place shortly after the first evidence for its existence in East Africa (Gabunia et al., 2001; Antón and Swisher, 2004), and evidence of the dispersal of Homo to East Asia by about 1.8 Ma is documented in China and Indonesia (Antón and Swisher, 2004; Zhu et al., 2004, 2008). This dispersal out of Africa is widely believed to have been facilitated by a major behavioral shift to increased hunting and meat consumption (Shipman and Walker, 1989). These hominins were quite variable in their cranial capacity (Spoor et al., 2007), probably due to sexual dimorphism. Studies of enamel formation show that their life history was like that of African apes rather than humans—they grew up quickly and died young (Dean et al., 2001). It is interesting to note that the Acheulean stone tool culture that is thought to typify H. erectus, which included the handaxe, had not been developed by the time their first fossils occurred. This species apparently used Oldowan technology until the Acheulean was invented at about 1.6 Ma; their dispersal to Eurasia, for example, took place without handaxes. The earliest strong evidence for the use of controlled fire occurs about 800 ka (Goren-Inbar et al., 2004).

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KNM-ER 3733, Homo erectus (or Homo ergaster)

This fossil is discovered by Bernard Ngeneo in 1975 at Koobi Fora in Kenya. Estimated age is 1.7 million years. This superb find consisted of an almost complete cranium. The brain size is about 850 cc, and the whole skull is similar to the Peking Man fossils. The discovery of this fossil in the same stratum as ER 406 (A. boisei) delivered the coup de grace to the single species hypothesis: the idea that there has never been more than one hominid species at any point in history. (Leakey and Walker 1976)

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An international research team working in Israel has discovered the oldest-known modern human bones ever found outside the African continent: an upper jawbone, including teeth, dated to between 175,000 and 200,000 years old. It shows humans left Africa at least 50,000 years earlier than we had thought.

The scientists unearthed the fossil at Misliya Cave, one in a series of prehistoric caves on Israel’s Mount Carmel. This region of the Middle East was a major migration route when humans spread out from African during the Pleistocene.  It provides the clearest evidence yet that our ancestors first migrated out of Africa much earlier than we previously believed. It also means that modern humans were potentially meeting and interacting during a longer period of time with other archaic human groups, providing more opportunity for cultural and biological exchanges.

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Homo sapiens—in the form of skulls and skeletons that are practically indistinguishable, even in brain size, from those of modern people—appears first in Africa about 200 ka (McDougall et al., 2005). Before this event there are many fossils that are usually allocated to H. heidelbergensis, as well as other more arcane names. Some of these fossils from Europe appear to be the ancestors of the Neanderthals, a group of hominins that evolved in the glacial climates of Eurasia. Other fossils from Africa are most likely the ancestors of Homo sapiens (White et al., 2003), and others recovered in Asia may not have had any descendants.

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Origins of Modern Humans:

Current data suggest that modern humans evolved from archaic humans primarily in East Africa.  A 195,000 year old fossil from the Omo 1 site in Ethiopia shows the beginnings of the skull changes that we associate with modern people, including a rounded skull case and possibly a projecting chin.  A 160,000 year old skull from the Herto site in the Middle Awash area of Ethiopia also seems to be at the early stages of this transition.  It had the rounded skull case but retained the large brow ridges of archaic humans.  Somewhat more advanced transitional forms have been found at Laetoli in Tanzania dating to about 120,000 years ago.  By 115,000 years ago, early modern humans had expanded their range to South Africa and into Southwest Asia (Israel) shortly after 100,000 years ago.  There is no reliable evidence of modern humans elsewhere in the Old World until 60,000-40,000 years ago, during a short temperate period in the midst of the last ice age.

Important Early Modern Homo sapiens Sites:

Date of Fossil
(years ago)
East Africa:
  Herto, Middle Awash 160,000-154,000
  Omo 1 195,000
  Laetoli 120,000
South Africa:
  Border Cave 115,000-90,000
  Klasies River Mouth 90,000
Israel:
  Skhul and Qafzeh 92,000-90,000
Australia:
  Lake Mungo 60,000-46,000
Asia:
  Annamite Mountains (Laos) 63,000
  Ordos (Mongolia) 40,000-20,000?
  Liujiang (China) 139,000-111,000?
  Zhirendong (China) 100,000 ?
  Zhoukoudian upper cave
(China)
27,000
Europe:
  Peştera cu Oase (Romania) 36,000-34,000
  Combe Capelle (France) 35,000-30,000
  Mladeč and Předmostí
(Czech Republic)
35,000-25,000
   Cro-Magnon (France) 27,000-23,000

Note:

Artifactual evidence indicates that modern humans were in Europe by at least 40,000 and possibly as early as 46,000 years ago.  Dating of the earliest modern human fossils in Asia is less secure, but it is likely that they were present there by at least 60,000 years ago and possibly 100,000 years ago.

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Limitations of fossil evidence:

The fossil record is an important but intrinsically limited source of evidence of the evolutionary history of organisms. The vast expanse of geological time and the rarity of fossilization prescribe that the fossil record can at best offer clues to the broad patterns of evolution. Even the detailed history of transitions from an ancestral horse (Eohippus) to the modern horse (Equus), which has been characterized as being “articulately represented,” remains sketchy despite the identification of “at least 12 genera and several hundred species.” Such extensive fossils offer no evidence of direct ancestor-descendant relations that would need to be proven to prove the notion of continuous descent from a common ancestor. The horse ancestor fossil record is considered to be the most detailed fossil record of all. For most modern species, however, there is a general lack of gradually sequenced intermediary forms. There are some fossil lineages that appear quite well-represented, such as from therapsid reptiles to the mammals, and between what are considered the land-living ancestors of the whales and their ocean-living descendants (Mayr 2001). Archaeopteryx has been viewed by many as representing an intermediate stage between reptiles and birds. Generally, however, paleontologists do not find a steady change from ancestral forms to descendant forms. Rather, they find discontinuities, or gaps in most every phyletic series (Mayr 2002). This has been explained both by the incompleteness of the fossil record and by proposals of speciation that involve short periods of time, rather than millions of years. Available gaps in fossil record may be more indicative and supportive towards speciation and abrupt changes rather than gradual evolution through phyletic transformation.

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Some of the reasons for the incompleteness of fossil records are:

  • In general, the probability that an organism becomes fossilized after death is very low;
  • Some species or groups are less likely to become fossils because they are soft-bodied;
  • Some species or groups are less likely to become fossils because they live (and die) in conditions that are not favorable for fossilization to occur in;
  • Many fossils have been destroyed through erosion and tectonic movements;
  • Some fossil remains are complete, but most are fragmentary;
  • Some evolutionary change occurs in populations at the limits of a species’ ecological range, and as these populations are likely to be small, the probability of fossilization is lower (punctuated equilibrium);
  • Similarly, when environmental conditions change, the population of a species is likely to be greatly reduced, such that any evolutionary change induced by these new conditions is less likely to be fossilized;
  • Most fossils convey information about external form, but little about how the organism functioned;
  • Using present-day biodiversity as a guide suggests that the fossils unearthed represent only a small fraction of the large number of species of organisms that lived in the past.

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Genetic Evidence: [vide supra DNA study and sequencing]

The fact that the genetic code is universal to all living things suggests that we once had a common ancestor. Comparing the DNA sequence of two organisms can give us an idea of how closely related they are. For instance, your DNA sequence will be more similar to a direct relative than a stranger. Your DNA is more similar to other members of the same species than it is to other species. The more closely two DNA sequences match, the more recently they would have shared a common ancestor. By analysing the DNA from different species Scientists can start to generate family trees called phylogenetic trees.

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Allan Wilson, Emile Zuckerkandl, and Linus Pauling pioneered the use of molecular approaches, which examined evolution at the scale of DNA and proteins showing that relationships among living and extinct primates can be inferred from genetics as well as fossils. Genetics too can be used as a “clock,” which compares the amount of genetic differences (mutations) between living organisms. Since mutations have predictable rates of change over time, they can be used to estimate how long ago a living species shared a common ancestor. The molecular clock cannot assign concrete dates and must be calibrated against independent evidence, such as the fossil record. Nevertheless, taking together the transdisciplinary evidence, we now have a robust understanding of the relationships between humans and apes.

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Genetic synonyms:

In a certain context, the words “round” and “circular” mean the same thing to an English speaker—they are synonyms. So too, there are “synonyms” in the genetic code—different sequences of DNA bases that mean the same thing to cells (that is, they cause the production of the same proteins). Mutations in the genetic code are often harmful, resulting in an organism not being able to successfully reproduce. But if the mutation results in a “synonym”, the organism would function the same and continue passing on its genes. Because of this we would expect the synonymous changes to be passed on much more effectively than non-synonymous changes. That is exactly what we find among the DNA of humans and chimpanzees: there are many more synonymous differences between the two species than non-synonymous ones. This is exactly what we would expect if the two species had a common ancestor, and so it provides further evidence that humans and chimpanzees were created through common descent from a single ancestral species.

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Genetic “scars”:

Just as scars stay on our bodies as reminders of past events, the DNA code contains “scars” and these are passed on from generation to generation. DNA scars result from the deletion or insertion of a block of bases (not just single base changes). Because we have a lot of these (hundreds of thousands) and they can be precisely located, they serve as a historical record of species. If we have the same scar as chimpanzees and orangutans, then the deletion or insertion must have occurred before these species diverged into separate populations. If we and chimpanzees have a certain scar but orangutans do not, we can conclude the deletion or insertion must have occurred after the common ancestor of chimps and humans separated from our common ancestor with orangutans. In this way we can create a detailed family tree of common ancestors.

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To illustrate the principle, imagine for a moment that you have a scar at a particular location on your body. Perhaps it is the result of a bad cut that occurred to your right little finger when you were seven years old. It’s at the tip and not the base of the finger. It’s on the inside of the finger near the middle, not on the left or the right side. It is a vertical cut, not horizontal, and it is one half inch long—not shorter and not longer. It is there because of a very specific event—an accident with a knife that happened when you were seven. The scar is not serving a purpose in your body. Its presence is solely the result of a particular event in history. In a manner that is completely analogous to this the genome gets damaged, and insertions and deletions are like the scars on a damaged finger. They can be positioned exactly. Indeed they can be resolved to 0.00000034 millimeters (a single DNA unit) out of the five thousand millimeters of DNA in a typical human chromosome. Sometimes when the cut is healed ten DNA units are deleted, other times one hundred, and other times just one. Sometimes the healing is associated with a small insertion of defined length. But unlike the scar on your finger, DNA scars are passed on to subsequent generations and so can be tracked through an ancestral lineage.

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Genetics has also confirmed that living humans have a limited genetic diversity indicating a series of population bottlenecks (temporary, drastic reductions in population size and therefore genetic variability, caused by earthquakes or disease, for example) and a limited ancestral gene pool (Foley 1994; Manica et al. 2007). Studies of genetic variation reveal that the greatest diversity can be found in African populations. This combined with evidence from female (mitochondrial DNA) and male (Y chromosome) specific histories confirm an African origin for our species and suggest our ancestors migrated out of Africa. In addition to helping researchers identify phylogeny, demographic history, and dispersal patterns, we can also identify areas of the human genome influenced by natural selection. Functional genes, such as those involved in infectious disease resistance; life history patterns; diet; skin, hair, and eye coloration; human cognition; and even language, have revealed areas of the genome that have been influenced by natural selection in humans (Enard et al. 2002; Tishkoff & Williams 2002; Lao et al. 2007; Preuss 2012).

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Darwin in Genetics:

For over 150 years, Darwin’s hypothesis that all species share a common ancestor has dominated the creation-evolution debate. Surprisingly, when Darwin wrote his seminal work, he had no direct evidence for these genealogical relationships—he knew nothing about DNA sequences. In fact, before the discovery of the structure and function of DNA, obtaining direct scientific evidence for common ancestry was impossible. Now, with online databases full of DNA-sequence information from thousands of species, the direct testing of Darwin’s hypothesis has finally commenced. One of the most commonly cited evidences for evolution is the hierarchical classification of life, which is based on anatomy and physiology. If evolution were true, then genetics should clearly reflect this pattern. A brief examination of DNA inheritance shows the theoretical basis for this evolutionary expectation. When life begins at conception, DNA is transmitted through both the sperm and the egg, but the process of transmission happens imperfectly. Thus, each successive generation grows more genetically distant from previous generations as each new fertilization event contributes more genetic mistakes to the lineage. By analogy, it’s as if a group of people were tasked with transcribing the text of a book and, in the process, made several errors with each transcription. If each flawed copy was used as the basis for the next copy, each successive transcription event would contribute more mistakes to the final product. Since the errors are cumulative, then comparing the number of mistakes between individual copies of the book would reveal which copies were transcribed earlier and which ones were transcribed later. Similarly, under the evolutionary paradigm, comparing the number of DNA mistakes between species should reveal which ones have a recent common ancestor and which ones have an older genealogical connection.  Darwin’s iconic “tree of life” embodies the sum of evolution’s relative predictions about species’ common ancestry, and many genetic observations seem to support his hierarchical depiction of the genealogical relationships among species. For example, humans tend to share more DNA with the great apes than with frogs, and these species share more DNA with one another than they do with insects. This is consistent with predicted nesting of the human evolutionary branch within the primate branch of the tree of life and with the clustering of vertebrate species with one another but not with invertebrates on the tree. These results would seem to confirm evolution.

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Archaeogenetics:

Archaeogenetics is the study of ancient DNA using various molecular genetic methods and DNA resources. This form of genetic analysis can be applied to human, animal, and plant specimens. Ancient DNA can be extracted from various fossilized specimens including bones, eggshells, faeces, and artificially preserved tissues in human and animal specimens. In plants, Ancient DNA can be extracted from seeds and tissues. Archaeogenetics provides us with genetic evidence of ancient population group migrations, domestication events, and plant and animal evolution. The ancient DNA cross referenced with the DNA of relative modern genetic populations allows researchers to run comparison studies that provide a more complete analysis when ancient DNA is compromised.

Africa:

Modern humans arose in Africa approximately 200 kya (thousand years ago). Examination of mitochondrial DNA (mtDNA), Y-chromosome DNA, and X-chromosome DNA indicate that the earliest population to leave Africa consisted of approximately 1500 males and females. It has been suggested by various studies that populations were geographically “structured” to some degree prior to the expansion out of Africa; this is suggested by the antiquity of shared mtDNA lineages. One study of 121 populations from various places throughout the continent found 14 genetic and linguistic “clusters,” suggesting an ancient geographic structure to African populations. In general, genotypic and phenotypic analysis have shown “large and subdivided throughout much of their evolutionary history.” Genetic analysis has supported archaeological hypotheses of a large-scale migrations of Bantu speakers into Southern Africa approximately 5 kya. Microsatellite DNA, single nucleotide polymorphisms (SNPs), and insertion/deletion polymorphisms (INDELS) have shown that Nilo-Saharan speaking populations originate from Sudan. Furthermore, there is genetic evidence that Chad-speaking descendants of Nilo-Saharan speakers migrated from Sudan to Lake Chad about 8 kya. Genetic evidence has also indicated that non-African populations made significant contributions to the African gene pool. For example, the Saharan African Beja people have high levels of Middle-Eastern as well as East African Cushitic DNA.

Europe:

Analysis of mtDNA shows that Eurasia was occupied in a single migratory event between 60 and 70 kya. Genetic evidence shows that occupation of the Near East and Europe happened no earlier than 50 kya. Studying haplogroup U has shown separate dispersals from the Near East both into Europe and into North Africa. Analysis of haplogroups V, H, and U5 support a “pioneer colonization” model of European occupation, with incorporation of foraging populations into arriving Neolithic populations. Furthermore, analysis of ancient DNA, not just extant DNA, is shedding light on some issues. For instance, comparison of neolithic and mesolithic DNA has indicated that the development of dairying preceded widespread lactose tolerance.

South Asia:

Studies of mtDNA line M suggest that the first occupants of India were Austro-Asiatic speakers who entered about 45-60 kya. The Indian gene pool has contributions from an African source population, as well as West Asian and Central Asian populations from migrations no earlier than 8 kya. The lack of variation in mtDNA lineages compared to the Y-chromosome lineages indicate that primarily males partook in these migrations. The discovery of two subbranches U2i and U2e of the U mtDNA lineage, which arose in Central Asia has “modulated” views of a large migration from Central Asia into India, as the two branches diverged 50 kya. Furthermore, U2e is found in large percentages in Europe but not India, and vice versa for U2i, implying U2i is native to India.

East Asia:

Analysis of mtDNA and NRY (non-recombining region of Y chromosome) sequences have indicated that the first major dispersal out of Africa went through Saudi Arabia and the Indian coast 50-100 kya, and a second major dispersal occurred 15-50 kya north of the Himalayas.

Americas:

Archaeogenetics has been used to better understand the populating of the Americas from Asia. Native American mtDNA haplogroups have been estimated to be between 15 and 20 kya, although there is some variation in these estimates. Genetic data has been used to propose various theories regarding how the Americas were colonized. Although the most widely held theory suggests “three waves” of migration after the LGM through the Bering Strait, genetic data have given rise to alternative hypotheses.

Australia and New Guinea:

Finally, archaeogenetics has been used to study the occupation of Australia and New Guinea. The aborigines of Australia and New Guinea are phenotypically very similar, but mtDNA has shown that this is due to convergence from living in similar conditions.  Non-coding regions of mt-DNA have shown “no similarities” between the aboriginal populations of Australia and New Guinea.  Furthermore, no major NRY lineages are shared between the two populations. The high frequency of a single NRY lineage unique to Australia coupled with “low diversity of lineage-associated Y-chromosomal short tandem repeat (Y-STR) haplotypes” provide evidence for a “recent founder or bottleneck” event in Australia. But there is relatively large variation in mtDNA, which would imply that the bottleneck effect impacted males primarily. Together, NRY and mtDNA studies show that the splitting event between the two groups was over 50kya, casting doubt on recent common ancestry between the two.

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Sequencing Y Chromosomes resolves discrepancy in Time to Common Ancestor of Males versus Females: a 2013 study:

The Y chromosome and the mitochondrial genome (mtDNA) have been used to estimate when the common patrilineal and matrilineal ancestors of humans lived. Authors sequenced the genomes of 69 males from nine populations, including two in which we find basal branches of the Y chromosome tree. They identify ancient phylogenetic structure within African haplogroups and resolve a long-standing ambiguity deep within the tree. Applying equivalent methodologies to the Y and mtDNA, they estimate the time to the most recent common ancestor (TMRCA) of the Y chromosome to be 120–156 thousand years and the mtDNA TMRCA to be 99–148 ky. Authors findings suggest that, contrary to prior claims, male lineages do not coalesce significantly more recently than female lineages. Dogma has held that the common ancestor of human patrilineal lineages, popularly referred to as the Y chromosome “Adam,” lived considerably more recently than the common ancestor of female lineages, the so-called mitochondrial “Eve.” However, authors conclude that the mitochondrial coalescence time is not substantially greater than that of the Y chromosome. Indeed, due to their moderate-coverage sequencing and the existence of additional rare divergent haplogroups, their analysis may yet underestimate the true Y TMRCA.

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Mitochondrial DNA of Neanderthal:

In July 1997, the first successful extraction of Neanderthal DNA was announced. In an article in the journal Cell, a team of German and American researchers led by Svante Pääbo (Krings et al. 1997) claimed to have extracted mitochondrial DNA (mtDNA) from a piece of bone cut from the upper arm of the first recognised Neanderthal fossil, the individual found at the Feldhofer grotto in the Neander Valley in Germany in 1856 (Kahn and Gibbons 1997, Ward and Stringer 1997). In 1999, scientists successfully extracted a 345 base pair sequence of mtDNA from a second Neanderthal, a 29,000 year-old fossil of a baby recently discovered in Mesmaiskaya cave in south-western Russia. (Ovchinnikov et al. 2000, Höss 2000) The results of this study were similar to the previous ones, putting the Mezmaiskaya specimen outside the range of modern human mtDNA. In 2000, scientists announced the sequencing of a third Neanderthal mtDNA specimen from a cave at Vindija, Croatia (Krings et al. 2000). When the three Neanderthals are compared with modern humans, all three of them cluster together, and apart from all modern humans.  Schmitz et al. (2002) reported on a fourth Neanderthal mtDNA sequence from the second Neanderthal fossil found at Feldhofer, the site in Germany at which the first Neanderthal fossil was found. It was closely related to the previous Neanderthal mtDNA sequences. Serre et al. (2004) were able to sequence mtDNA from four other Neanderthal fossils, along with mtDNA from five early modern humans. The four Neanderthals all had mtDNA similar to those found in the previous Neanderthals. Serre and his colleagues found no evidence of mtDNA gene flow between modern humans and Neanderthals in either direction, but could not rule out the possibility of limited gene flow. Interestingly, the mtDNA sequences from the Vindija Neanderthals, which have a less extreme Neanderthal anatomy than the classic Neanderthals, and are considered transitional between modern humans and classic Neanderthals by some scientists, were no closer to modern humans than the rest of the Neanderthal fossils. Up to 2008, 17 mtDNA sequences have been extracted from Neanderthal fossils (Green et al. 2008). All these sequences support the conclusion that Neanderthal mtDNA is outside the range of modern human mtDNA, and strongly indicate that Neanderthals made no lasting contribution to the human mtDNA gene pool. (This does not prove that they made no contributions to the nuclear DNA of any modern humans, however.) The studies of Neanderthal mtDNA do not show that Neanderthals did not or could not interbreed with modern humans. But the lack of diversity in Neanderthal mtDNA sequences, combined with the large differences between Neanderthal and modern human mtDNA, strongly suggests that Neanderthals and modern humans developed separately, and did not form part of a single large interbreeding population. However Neanderthals apparently remained capable of interbreeding with humans, and did so with an early population of modern humans in the Middle East about 70,000 years ago.

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A complete Neanderthal mitochondrial genome sequence determined by high-throughput sequencing a 2009 study:

A complete mitochondrial (mt) genome sequence was reconstructed from a 38,000-year-old Neanderthal individual using 8,341 mtDNA sequences identified among 4.8 Gb of DNA generated from ~0.3 grams of bone. Analysis of the assembled sequence unequivocally establishes that the Neanderthal mtDNA falls outside the variation of extant human mtDNA and allows an estimate of the divergence date between the two mtDNA lineages of 660,000±140,000 years. Of the 13 proteins encoded in the mtDNA, subunit 2 of cytochrome c oxidase of the mitochondrial electron transport chain has experienced the largest number of amino acid substitutions in human ancestors since the separation from Neanderthals. There is evidence that purifying selection in the Neanderthal mtDNA was reduced compared to other primate lineages suggesting that the effective population size of Neanderthals was small.

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A Draft Sequence of the Neanderthal Genome 2010 study:

Neanderthals, the closest evolutionary relatives of present-day humans, lived in large parts of Europe and western Asia before disappearing 30,000 years ago. Authors present a draft sequence of the Neanderthal genome composed of more than 4 billion nucleotides from three individuals. Comparisons of the Neanderthal genome to the genomes of five present-day humans from different parts of the world identify a number of genomic regions that may have been affected by positive selection in ancestral modern humans, including genes involved in metabolism and in cognitive and skeletal development. They show that Neanderthals shared more genetic variants with present-day humans in Eurasia than with present-day humans in sub-Saharan Africa, suggesting that gene flow from Neanderthals into the ancestors of non-Africans occurred before the divergence of Eurasian groups from each other.

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Comparative analysis of human, Neanderthal and chimpanzee genomes:

The draft Neanderthal genome sequence consists largely of 35- to 100-bp sequence reads that provide ∼1× coverage (Pennisi 2009). De novo sequence assembly is not possible with such data—in fact, it is a daunting computational challenge even with >40× coverage of a modern human genome (Simpson et al. 2009). Initial human, Neanderthal, and chimpanzee sequence comparisons will thus involve tiling Neanderthal reads onto the human and chimpanzee reference genomes. These analyses will largely be limited to detecting lineage-specific substitutions and small insertions or deletions (indels). Some insight may be gained into segmental duplications or other large-scale genome rearrangements, but it is not clear how this can be achieved. The draft Neanderthal genome will thus provide three novel data sets: a genome-wide map of substitutions and indels that appear to be specific to the modern human reference genome relative to Neanderthal and chimpanzee; a map of Neanderthal-specific changes, which will be dominated by damage-induced errors; and a map of shared human–Neanderthal-derived changes relative to chimpanzee, which may include modern human contaminants as seen in the figure below A. The most informative of these will be the map of apparent modern human-specific substitutions, which will complement existing maps of human-specific fixed sequence differences obtained from human–chimpanzee comparisons. Coupled with existing data sets of human polymorphisms and the large number of individual human genomes currently being sequenced, these maps will identify sequence differences arising since the modern human–Neanderthal divergence that are fixed in all humans.

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Analyses of human and Neanderthal polymorphism are somewhat more complicated. Many human polymorphisms are expected to predate the human–Neanderthal split and thus may be present in Neanderthal as well. Consequently, fixed substitutions in modern humans may be polymorphic in Neanderthal, as may be sites where human and Neanderthal are derived relative to chimpanzee. Human polymorphisms where the Neanderthal reference genome has the ancestral allele may nevertheless be polymorphic in Neanderthal; this will confound efforts to date human polymorphisms based on the Neanderthal allele state. It is presently not clear how the effects of Neanderthal polymorphism on substitution maps will be addressed.

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A Neanderthal reference genome would also complement ongoing efforts to annotate uniquely human cis-regulatory functions in the genome. Several recent studies have identified known or putative regulatory sequences that show high rates of nucleotide substitution on the human lineage, which may be due to positive selection for changes in regulatory functions (Pollard et al. 2006; Prabhakar et al. 2006; Haygood et al. 2007). These efforts have largely focused on promoters and highly conserved noncoding sequences (CNSs), as CNSs are known to be enriched in transcriptional enhancers with in vivo developmental activities (Pennacchio et al. 2006; Visel et al. 2008). For example, a recent global study of human promoters found evidence of positive selection in promoters of genes involved in neural development and nutrition (Haygood et al. 2007). Another study surveyed patterns of human-specific nucleotide substitution in >110,000 CNSs in the genome and identified 992 that showed statistically significant evidence of evolutionary acceleration (Prabhakar et al. 2006). These human-accelerated conserved noncoding sequences (HACNSs), which are known to include developmental enhancers, were overrepresented near genes involved in neuronal cell adhesion. This finding, along with the observation that the promoters of neuronal genes show evidence of human-specific positive selection, suggests that cis-regulatory changes may have had a profound impact on human brain evolution. Neanderthal genome sequence would also provide insight into the evolutionary origin of regulatory RNAs with putative human-specific functions: In one study of human-specific sequence acceleration in transcribed and non-transcribed sequences that identified 49 human accelerated regions (HARs), the most accelerated element, HAR1, is part of a noncoding RNA expressed in the developing human brain (Pollard et al. 2006b).

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Comparison of the human and Neanderthal reference genomes would also place bounds on the evolutionary age of individual sequence changes that generate human-specific functions. For example, one of the most rapidly evolving CNSs in the genome, identified as HACNS1 or HAR2 in the studies described above, has accumulated 16 human-specific substitutions despite being highly conserved in all nonhuman terrestrial vertebrates (see figure above B). HACNS1 functions as a transcriptional enhancer in multiple structures in embryonic day (E) 11.5 and E13.5 mouse embryos, including in the developing anterior limb (Prabhakar et al. 2008). However, the orthologous chimpanzee and rhesus enhancers fail to drive expression in the limb, suggesting HACNS1 has gained human-specific function in vivo. Notably, humanized chimpanzee enhancers, in which 13 of the 16 human-specific substitutions were introduced into the chimpanzee sequence, drove expression in the limb, indicating that the substitutions identified in the computational screen were directly responsible for the functional change. These substitutions could have arisen at any point since the divergence of the human and chimpanzee lineages. Comparing HACNS1 with its Neanderthal ortholog would establish whether some or all of these substitutions—and the functions they confer—are unique to modern humans (Figure above B).

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These studies illustrate a general strategy toward an understanding of biological differences between modern humans and Neanderthals, in which the first step is the reverse genetic analysis of genes and gene regulatory elements showing human-specific or Neanderthal-specific sequence changes. In this approach, changes in basic molecular functions, such as enhancer activity, protein–DNA interactions, or receptor-ligand binding affinity are identified in synthetic assays. The phenotypic consequences of these molecular changes can then be assessed in mouse models: The data from such studies, combined with a growing body of information on human gene function, the effects of genetic variation on human phenotypes, and comprehensive efforts to functionally annotate the human genome, would provide the foundation for more sophisticated hypotheses concerning the biological similarity of modern humans and Neanderthals than can be generated from the paleoanthropological record alone.

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Despite many technical and analytical challenges, a Neanderthal genome sequence has been generated and is certain to advance our understanding of modern human evolution. Are modern humans fundamentally different from all archaic human species? Neanderthals were certainly intelligent: They fashioned recognizably human tools and lived in established communities, which alone suggests they were sufficiently “human”. It is hoped that direct comparison of the human and Neanderthal genomes will reveal whether our talents for invention, language, and abstract thought—the basis of our perceived uniqueness among species—are truly unique to us. It may be that Neanderthals lacked essential modern human characteristics. However, there is a long road ahead, and we should not be surprised if we discover that we are not as different from our extinct relatives as we believe.

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Comparing genomes of four human populations: Modern Eurasians, modern Africans, Neanderthals and Denisovans:

New look at archaic DNA rewrites human evolution story: 2017 study:

Hundreds of thousands of years ago, the ancestors of modern humans diverged from a lineage that gave rise to Neanderthals and Denisovans. Yet the exact relationship between these ancient groups has remained unclear.

Now, a new method of studying DNA is beginning to unravel the mystery – and the findings appear to contradict conventional theories about human evolution.  The study claims that the number of Neanderthals that walked the Earth could have been tens of thousands more than scientists first thought. It also suggests Neanderthals and Denisovans diverged from each other around 744,000 years ago – around 300,000 earlier than previously believed. This implies that Homo heidelbergensis – which lived in Africa, Europe and western Asia between 600,000 and 200,000 years ago – was an early Neanderthal. The team compared the genomes of four human populations: Modern Eurasians, modern Africans, Neanderthals and Denisovans. They estimated the percentage of Neanderthal genes flowing into modern Eurasian populations, the date at which archaic populations diverged, and their population sizes.  The discovery was made after researchers came up with a new way to analyse our ancestors’ DNA.

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Many researchers have estimated there were only about 1,000 Neanderthals, which shared 99.7 per cent of their DNA with modern humans. But scientists from the University of Utah have now estimated the figure was likely in the ‘tens of thousands’. A team led by Professor Alan Rogers created used an analysis technique that recreates the early history of ancient human populations including Neanderthals and Denisovans. They found the Neanderthal-Denisovan lineage nearly went extinct after separating from modern humans. Then, just 300 generations later, Neanderthals and Denisovans diverged from each other – around 744,000 years ago. The global Neanderthal population then grew to tens of thousands of individuals living in fragmented, isolated populations scattered across Eurasia. Professor Rogers said: ‘This hypothesis is against conventional wisdom, but it makes more sense than the conventional wisdom.’  With only limited samples of fossil fragments, anthropologists must assemble the history of human evolution using genetics and statistics. An earlier study in 2015 showed estimates of a 1,000-strong Neanderthal population was underrepresented if they were subdivided into isolated, regional groups.

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The new research suggests Neanderthals and Denisovans diverged from each other around 744,000 years ago – much earlier than previously believed. This could prove that heidelbergensis was an early Neanderthal. The similarity between Neanderthal, Homo heidelbergensis and Homo sapien fossils means researchers previously thought heidelbergensis fossils are mere variants of Homo sapiens. Professor Rogers said: ‘You’re trying to find a fingerprint of these ancient humans in other populations. ‘It’s a small percentage of the genome, but it’s there.’  They compared the genomes of four human populations: Modern Eurasians, modern Africans, Neanderthals and Denisovans. The two ancient samples – both the Neanderthal and the Denisovan – came from Denisova Cave, in the Altai Mountains of Siberia. The Utah team used two modern data sets, both from the ‘1000 Genomes Project’. The scientists found the Neanderthal-Denisovan lineage nearly went extinct after separating from modern humans. Then, just 300 generations later, Neanderthals and Denisovans diverged from each other – around 744,000 years ago  The researchers analysed a few million nucleotide sites that shared a gene mutation in two or three human groups, and established 10 distinct nucleotide site patterns. The new method confirmed previous estimates that modern Eurasians share about two per cent of Neanderthal DNA. But other findings questioned established theories. Their analysis revealed that 20 per cent of nucleotide sites showed a mutation only shared by Neanderthals and Denisovans, a genetic timestamp marking the time before the archaic groups diverged. The team calculated that Neanderthals and Denisovans separated about 744,000 years ago, much earlier than any other estimation of the split.

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Ancient DNA carries advantages:

Modern humans carry traces of DNA from mixing with other hominids, including Neanderthals and Denisovans. Recently researchers at the University of Washington School of Medicine analysed the DNA of 1,500 people, including those from Europe, Asia and the Pacific islands, to see where these ancient genes remain. They identified 126 areas of the modern human genome where ancient DNA persists. They found genes relating to the immune system and skin function. Neanderthal gene expression likely contributes to traits such as height and even our susceptibility to lupus and schizophrenia.  Scientists believe these genes from our extinct cousins helped modern humans to thrive as they moved outwards from the African continent.

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Scientists say they have Genetic Evidence for Evolution 2018 study:

Scientists have presented archaeological evidence, anatomical evidence and now they say they have genetic evidence that demonstrates Charles Darwin was right when he suggested new species arise through a process known as natural selection.  A team led by William McGinnis, a biologist at the University of California at San Diego, showed that a single mutation in a particular class of genes known as Hox genes can lead to big changes in the body. These big changes, the researchers say, could have played a significant role in the evolution of some new species. Past research has shown that Hox genes act as master switches that turn on and off other genes during embryonic development. The team found that by mutating Hox genes in multi-limbed crustaceans and millipedes they could effectively block the development of limbs in these animals. This mutation, they say, could have led to the evolution of insects, which have only six legs and emerged suddenly some 400 million years ago, long after crustaceans were on the scene.  “One of the big questions people have for evolution is, how can you get dramatic rearrangements of bodies,” said McGinnis. “Up until now there hasn’t been much evidence of how this happens.” The discovery of homeotic genes (those that control the transition of one body part into another) shows how major morphological changes (macromutations) can occur through alteration of the basic body plan or repositioning of structures. The Hox gene complex controls basic segmentation of the body in both arthropods and vertebrates. Changes to this complex can produce new body plans, extra appendages, or extra segments in a single generation.

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Interbreeding:

Did modern humans interbreed with other human species?

As modern humans spread, they replaced all other human species. Homo heidelbergensis was replaced by modern humans in Africa and Europe, Homo erectus was replaced in Asia and Homo neanderthalensis was replaced in Europe. The most extreme version of this model suggests that modern humans replaced the older humans without any interbreeding. Less extreme versions allow for some interbreeding between these populations but suggest that gene flow and mixing between these different species was extremely limited.

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Groundbreaking analysis of the Neanderthal genome (nuclear DNA and genes) published in 2010 supports the less extreme ‘Out of Africa’ model. Results show that modern humans and Neanderthals did interbreed, although on a very limited scale. Researchers compared the genomes of five modern humans with the Neanderthal, discovering that Europeans and Asians share about 1-4% of their DNA with Neanderthals and Africans none. This suggests that modern humans bred with Neanderthals after moderns left Africa but before they spread to Asia and Europe. The most likely location is the Levant, where both species co-existed for thousands of years at various times between 50-90,000 years ago. Interestingly, the data doesn’t support wide-scale interbreeding between the species in Europe, where it would have been most likely given their close proximity. Researchers are now questioning why interbreeding occurred on such a low scale, given that it was biologically possible. The answer may lie in cultural differences. Another probable example of interbreeding between modern humans and other human species was also published in 2010. DNA from a tooth and finger bone excavated from Denisova cave in Russia, showed these remains belonged to a genetically distinct group of humans distantly related to Neanderthals and even more distantly related to Homo sapiens. The study also revealed that these ‘Denisovans’ interbred with the ancestors of modern Melanesians and Aboriginal Australians as the DNA of both groups today contains 4% to 6% Denisovan DNA (it has not been found in other Eurasian groups sampled). This may be due to rare encounters between modern humans and Denisovans as moderns migrated through South-East Asia and on to Melanesia. What species the Denisovans belonged to is unknown, but it is suggested they may be Homo heidelbergensis, whose remains have been found in the correct timespans and locations but whose DNA has yet to be extracted (and may never be due to the age of the remains).

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Neanderthal genome shows evidence of early human interbreeding, inbreeding a 2013 study:

The most complete sequence to date of the Neanderthal genome, using DNA extracted from a woman’s toe bone that dates back 50,000 years, reveals a long history of interbreeding among at least four different types of early humans living in Europe and Asia at that time, according to UC Berkeley scientists.

Figure above shows family tree of the four groups of early humans living in Eurasia 50,000 years ago and the gene flow between the groups due to interbreeding. The comparison shows that Neanderthals and Denisovans are very closely related, and that their common ancestor split off from the ancestors of modern humans about 400,000 years ago. Neanderthals and Denisovans split about 300,000 years ago.

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Darwin and Mendel:

When scientists today work to decode the human genome, they use high-tech methods to view the microscopic chromosomes and even pluck individual genes out of a cell. But in Darwin’s time, it was impossible to see any of that. No one was sure how animals or plants passed down traits. And Darwin knew that the lack of an explanation for heredity left a big gap in his theory of natural selection. In one of the great triumphs of scientific experimentation, Austrian biologist and monk Johann Gregor Mendel, Darwin’s contemporary, solved this problem in the mid-nineteenth century. The results of Mendel’s carefully designed and meticulously executed experiments, which involved nearly 30,000 pea plants followed over eight generations, were ignored until long after both he and Darwin were dead.

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Darwin, like many of his contemporaries, speculated that characteristics of the parents were blended — like mixing paint — as they passed to the offspring. But if that were true, some of Darwin’s critics pointed out, then how could a single fortunate mutation be spread through a species? It would be blended out, just as a single drop of white paint would be in a gallon of black. Mendel read Darwin with deep interest, but he disagreed with the blending notion, hypothesizing instead that traits, such as eye color or height or flower hues, were carried by tiny particles that were inherited whole in the next generation. The patient monk carefully bred and cross-bred pea plants to see how a few specific traits — height was one — were passed down. When Mendel bred a tall plant to a short one, all of the offspring were always tall, never blending to medium size. When he then bred those offspring together, three out of four of their offspring were tall, but one was short. Mendel knew exactly what this meant. Height was passed down in a particle we now call a gene (though Mendel never used that term himself). A plant was short or tall depending on the random combination of genes it inherited. So an adaptive mutation could spread slowly through a species and never be blended out. Darwin’s theory of natural selection, building on small mutations, could work. But no one at the time understood the implications of Mendel’s experiments. He soon left biology to focus on running his monastery. Only in 1900 was his work rediscovered. Only then did Mendel — who had worked without a microscope, without computers, but with a thoughtful hypothesis, a carefully designed experiment, and enormous patience — receive the credit for one of the great discoveries in the history of science.

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What’s the difference between Darwin and Mendel?

Mendel was looking into how different traits displayed by parents get propagated to offspring (not mechanisms – he was far early for that – but rules we now recognise as dominant and recessive alleles on homologous chromosomes). Darwin was looking into how slight differences in successive generations lead to significantly different populations and ultimately to speciation. Mendel learned about genetics.  He figured out how traits carried by a parent would be passed onto their offspring.  He didn’t figure out that all organisms come from a single source through evolution and the formation of new species. Darwin learned that when certain traits are passed from parents to offspring, this results in variations in individuals that are passes onto the succeeding generations.  He realized that offspring which inherit traits that are a better “fit” for their environment would tend to breed more successfully than the less fit – and that this mechanism would result in evolution and the formation of new species. The whole picture only comes into focus when you fold the two sets of findings together and stir in a dash of James Watson and Francis Crick’s discovery of how DNA works – upon which Mendel and Darwin’s discoveries rest.

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Mendel’s Laws of Inheritance:

Darwin contributed to the modern understanding of biological evolution by thoroughly documenting the variation of living forms and by identifying the process of natural selection. But Darwin did not understand how individuals pass on traits to their offspring. This discovery, and the study of heredity, was left to the experiments of an Austrian monk, Gregor Mendel (1822–1884). During the 1860s, Mendel began a series of breeding experiments with pea plants. The results of these experiments revolutionized biological thought.

Gregor Mendel’s pea plant experiment consisted of examining the pollination process of pea seeds and what traits were passed on to their offspring.  Upon finishing his experiment, he concluded 3 things:

  • The inheritance of each trait was determined by units (genes) that were unchanged when passed on to decedents
  • That an individual inherits one such trait from each parent
  • That a trait may not show up in an individual but maybe passed on to future offspring

Mendel developed a set of laws from his experiments. Mendel’s experiments told him that there were two “components” used to code for each trait and that some traits seem to dominate others. An individual component is now known as an allele.

The first law, the Law of Segregation, states that during fertilization each parent passes on one allele for each trait. Which allele the offspring would get from the parents is random.

The second law, the Law of Independent Assortment, states that transmission of one trait does not affect the transmission of other traits. We only described the experiments for one trait, pea color. In fact, Mendel and his fellow monks conducted experiments on six other traits; pea shape (round or wrinkled), seed color (gray or white), stem length, color of unripe pod (green or yellow), position of the flower (terminal or axial) and form of the ripe pod (inflated or constricted). The second law means that the inheritance of a green unripe pod should not influence the inheritance of a terminal flower.

The third law, the The Law of Dominance, states that one type of allele (the dominant) could mask the other (the recessive). This is now considered a general principle and not a law.

Mendel’s Laws of Inheritance helped revive Darwin’s theory. They would also prove tremendously important to the future of biology and medicine, affecting the lives of billions of people. A completely new discipline within Biology, Genetics, arose from Mendel’s work. New hybrid food strains were developed that were more productive, more nutritious, more disease resistant or had better taste. The Green Revolution and foods that we take for granted such as canola oil were largely the product of Mendelian genetics.  We now know Mendel’s particles or units of inheritance as genes. A gene can be considered a deoxyribonucleic acid (DNA) sequence that encodes the production of a particular protein or portion of a protein. In combination, these DNA sequences determine the physical characteristics of an organism.

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The world’s most influential biologists, “Darwin and Mendel were contemporaries to many and yet the initial acceptance of their ideas suffered very different fates” (Walsh 2012). Darwin theorized evolution and its complex traits (concepts from population and quantitative genetics) whilst Mendel was concerned with the “transmission of traits from a genetic basis.” Combining Darwin’s theory of evolution with Mendel’s genetics was the most important breakthrough in biology as it triggered a cascade of a whole host of other biological discoveries including DNA (Mayr 1997), the understanding that bacteria evolve which has enabled us to devise methods of dealing with the diseases that they causes and also the disentanglement of the complex relationships between animals and plants within communities enabling us to foresee some of the consequences when we start to interfere with them. The modern theory of synthetic evolution looks to combine Darwin theory of natural selection and Mendel’s conclusions.  According to the theory, evolution is the change of genes in a given population over a number of generations.  This change could be brought on through a number of factors including migration, change in landscape, change in food supply, or introduction of a new predator.  Darwin’s theories were mainly supported through observation and note taking whereas Gregor Mendel was able to explain these modifications through conclusive experimental evidence. Darwin’s observation took place 30 years prior to Mendels experiments and were publicized halfway through Mendel’s pea plant experiment.  Unlike Mendel, Darwin’s work was available for the masses, even though it lacked several important explanations that would have aided his theory of natural selection.  This being said, Darwin does deserve some credit for discovering evolution, but Mendel deserves credit for discovering the reasons on why evolution occurs.  The reason why Darwin receives more credit than Mendel is because he took the initiative when he decided to publicize his work.  On the other hand, Gregor Mendel was a Monk, therefore his religious believes may have played a factor in choosing not to publicize his work. In conclusion, Darwin was able to get the ideas of evolution out there but he wasn’t able to fully explain the reasons about why natural selections take place. Mendel’s work provided those reasons without digging into the concept of evolution.  The combination of the works created by Darwin and Gregor has allowed for the mass acceptance of evolution.

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Misconceptions about population genetics:

  1. Each trait is influenced by one Mendelian locus.

Before learning about complex or quantitative traits, students are usually taught about simple Mendelian traits controlled by a single locus — for example, round or wrinkled peas, purple or white flowers, green or yellow pods, etc. Unfortunately, students may assume that all traits follow this simple model, and that is not the case. Both quantitative (e.g., height) and qualitative (e.g., eye color) traits may be influenced by multiple loci and these loci may interact with one another and may not follow the simple rules of Mendelian dominance.

  1. Each locus has only two alleles.

Before learning about complex traits, students are usually taught about simple genetic systems in which only two alleles influence a phenotype. Because students may not have made connections between Mendelian genetics and the molecular structure of DNA, they may not realize that many different alleles may be present at a locus and so may assume that all traits are influenced by only two alleles.

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The ‘modern synthesis’: Synthetic theory of evolution:

 

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In the 1920s and 1930s the so-called modern synthesis connected natural selection and population genetics, based on Mendelian inheritance, into a unified theory that applied generally to any branch of biology. The modern synthesis explained patterns observed across species in populations, through fossil transitions in palaeontology, and complex cellular mechanisms in developmental biology. The publication of the structure of DNA by James Watson and Francis Crick in 1953 demonstrated a physical mechanism for inheritance. Molecular biology improved our understanding of the relationship between genotype and phenotype. Advancements were also made in phylogenetic systematics, mapping the transition of traits into a comparative and testable framework through the publication and use of evolutionary trees. In 1973, evolutionary biologist Theodosius Dobzhansky penned that “nothing in biology makes sense except in the light of evolution,” because it has brought to light the relations of what first seemed disjointed facts in natural history into a coherent explanatory body of knowledge that describes and predicts many observable facts about life on this planet.

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The modern synthesis was the early 20th-century synthesis reconciling Charles Darwin’s theory of evolution and Gregor Mendel’s ideas on heredity in a joint mathematical framework. Julian Huxley coined the term in his 1942 book, Evolution: The Modern Synthesis.

The basic postulate of the synthetic theory is that evolution proceeds principally as a result of the interaction between five indispensable processes:

  1. Mutation:

Alteration in the chemistry of gene (DNA) is able to change its phenotypic effect this is called point mutation or gene mutation. Mutation can produce drastic changes which may be deleterious or harmful and lethal or can remain insignificant. There are equal chances of a gene to mutate back to normal. Most of the mutant genes are recessive to normal gene and these are able to express phenotypically only in homozygous condition. Thus, gene mutation tends to produce variations in the offspring.

  1. Variation or Recombination:

Recombination that is, new genotypes from already existing genesis of several types : (a) the production of gene combinations containing the same individual two different alleles of the same gene, or the production of heterozygous individuals (meisois); (b) the random mixing of chromosomes from two parents during sexual reproduction to produce a new individual; (c) the exchange between chromosomal pairs of particular alleles during meiosis, called crossing over, to produce new gene combinations. Chromosomal mutations such as deletion, duplication, inversion, translocation and polyploidy also result in variation.

  1. Heredity:

The transmission of variations from parent to offspring is an important mechanism of evolution. Organisms possessing helpful hereditary characteristics are favoured in the struggle for existence. As a result, the offspring are able to benefit from the advantageous characteristics of their parents.

  1. Natural selection:

It brings about evolutionary change by favouring differential reproduction of genes which produces change in gene frequency from one generation to the next. Natural selection does not produce genetic change, but once it has occurred it acts to encourage some genes over others. Further, natural selection creates new adaptive relations between popula­tion and environment by favouring some gene combinations, rejecting others and constantly modifying and moulding the gene pool.

  1. Isolation:

Isolation of organisms of a species into several populations or groups under psychic, physiological or geographical factors is supposed to be one of the most significant factors responsible for evolution. Geographical barriers include physical barriers such as rivers, oceans, high mountains which prevent interbreeding between related organisms. Physiological barriers help in maintaining the individuality of the species, since the isolations known as reproductive isolation do not allow the interbreeding amongst the organisms of different species.

This is also called Neo-Darwinism.

In addition, three accessory factors affect the working of these five basic factors; Migration of individuals from one population to another as well as hybridization between races or closely related species both increase the amount of genetic variability available to a popu­lation. The effects of chance acting on small populations may alter the way in which natural selection guides the course of evolution (Stebbins, 1971).

Speciation (origin of new species):

An isolated population of a species independently develops different types of mutations. The latter accumulate in its gene pool. After several generations, the isolated population becomes genetically and reproductively different from other so as to constitute a new species.

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The modern synthesis also addressed the relationship between the broad-scale changes of macroevolution seen by palaeontologists and the small-scale microevolution of local populations of living organisms. The synthesis was defined differently by its founders, with Ernst Mayr in 1959, G. Ledyard Stebbins in 1966 and Theodosius Dobzhansky in 1974 offering differing numbers of basic postulates, though they all included natural selection, working on heritable variation supplied by mutation.

Natural selection vis-à-vis synthetic theory of evolution occurs in the following way:

  • Individuals in a species show a wide range of variation.
  • This variation is because of differences in genes.
  • Individuals with characteristics most suited to the environment are more likely to survive and reproduce.
  • The genes that allowed the individuals to be successful are passed to the offspring in the next generation.

Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve.

Other major figures in the synthesis included E. B. Ford, Bernhard Rensch, Ivan Schmalhausen, and George Gaylord Simpson. An early event in the modern synthesis was R. A. Fisher’s 1918 paper on mathematical population genetics, but William Bateson, and separately Udny Yule, were already starting to show how Mendelian genetics could work in evolution in 1902. Different syntheses followed, accompanying the gradual breakup of the early 20th century synthesis, including with social behaviour in E. O. Wilson’s sociobiology in 1975, evolutionary developmental biology’s integration of embryology with genetics and evolution, starting in 1977, and Massimo Pigliucci’s proposed extended evolutionary synthesis of 2007. Since the beginning of the 21st century and in light of discoveries made in recent decades, some biologists have argued for an extended evolutionary synthesis, which would account for the effects of non-genetic inheritance modes, such as epigenetics, parental effects, ecological and cultural inheritance, and evolvability.

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Extended evolutionary synthesis:

In recent decades, scientists have shown that cells can use a range of molecules to control which of their genes are turned on or off, through a process known as epigenetics. Basically, just having a gene isn’t enough, you need it to be made into a protein to affect an organism. But epigenetic processes, such as methylation, can be used to stop that happening. And researchers have shown that these epigenetic changes can actually be passed down, to allow offspring to better adjust to new challenges. Epigenetic changes are more flexible than genetic changes, but they can have just as big an impact on the way an organism behaves or looks. The quality of food a woman gets while she’s pregnant can influence the size and health of her baby, and those influences can last until adulthood. Modern synthesis doesn’t account for those epigenetic changes, but extended evolutionary synthesis would. And it could help explain some of the evolutionary mysteries in human history. For example, why so many fossils from the Homo genus that seemingly belong to the same species can look so similar in some ways, but so different in others – such as height and stature.

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Extended evolutionary synthesis could also help to explain the birth of agriculture around 10,000 years ago. We know that neolithic humans at the time started domesticating crops and animals, and transitioned from a hunter gatherer lifestyle to an agricultural one, laying the groundwork for modern civilisation. But researchers have been puzzled as to how this happened, based on our understanding of modern evolutionary synthesis. Modern synthesis would suggest that natural selection drove our ancestors to give up foraging and start growing crops instead, because it delivered the best payoff. But growing crops would have taken a long time, and so scientists have struggled to explain how it would have initially benefitted our ancestors. One hypothesis is that maybe the switch to agriculture occurred during a climate shift, when hunter gathering became harder than ever before. But there’s been no evidence of that occurring. Perhaps a better way of thinking about the transition is through the lens of extended evolutionary synthesis – maybe humans, not natural selection, steered their own evolution, and simply decided to start farming, whether or not there was initial payoff. This is a process known as niche construction, where an organism adapts to their environment in new ways that don’t necessarily have anything to do with genetics. Those changes can be passed down, and can shift the rest of the environment as a result. So for now, extended evolutionary synthesis is just a hypothesis, and while there have been a lot of great minds thinking about how it could work, we need more evidence to figure out if it actually works.

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Climate and evolution:

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Worldwide climate changes:

The Earth’s climate is not stable and fluctuates between colder periods called Ice Ages, and warmer periods known as Interglacials. It is possible to determine when these different climatic conditions occurred in the past by studying oxygen found in ice cores, speleothems (stalactites and stalagmites) and the remains of certain ocean creatures such as the tiny shelled Foraminifera. Oxygen is a useful indicator of past climates because it is plentiful and occurs in different forms. Some of those forms are more common in the atmosphere during cold periods than during warm periods. The forms of oxygen that were present at different times in the past reveal the pattern of past cold and warm periods. During cold periods, such as Ice Ages, the oceans and the shells of ocean dwelling Foraminifera contain a higher proportion of oxygen-18 (a heavy isotope of oxygen) than oxygen-16. This occurs because oxygen-16 is relatively light and quicker to evaporate. This oxygen-16 falls to the ground as rain or snow and, during an Ice Age, becomes locked-up in glaciers and ice sheets. During warmer periods the ice melts and oxygen-16 is returned to the oceans where it is incorporated into Foraminifera shells. Foraminifera are single-celled ocean creatures that often have a shell made of calcium carbonate. Some species of Foraminifera are better adapted to living in cold water, others are adapted to life in warm water. The shells of these different species can be identified from sediments cored out of the sea bed and can indicate the temperature of the ocean in past times. In addition, the proportions of oxygen-18 and oxygen-16 within their shells can reveal past sea temperatures and climates. Diatoms are types of single-celled algae with cell walls made of silica. Their microscopic silica ‘skeletons’ accumulate on the bottom of lakes and oceans and can be retrieved from sediment cores to provide information about the water conditions in previous times. Prehistoric soil can be analysed for its texture, which influences the type of plant that can grow in the soil, and also for its chemical composition. Trees and woody plants contain different types of carbon compared with grasses. These carbon isotopes remain in the soil after the plant decomposes and can be detected by chemical analysis.

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Climate Fluctuation and evolution:

Paleoanthropologists – scientists who study human evolution – have proposed a variety of ideas about how environmental conditions may have stimulated important developments in human origins.  Diverse species have emerged over the course of human evolution, and a suite of adaptations have accumulated over time, including upright walking, the capacity to make tools, enlargement of the brain, prolonged maturation, the emergence of complex mental and social behavior, and dependence on technology to alter the surroundings. The period of human evolution has coincided with environmental change, including cooling, drying, and wider climate fluctuations over time. How did environmental change shape the evolution of new adaptations, the origin and extinction of early hominin species, and the emergence of our species, Homo sapiens?  (‘Hominin’ refers to any bipedal species closely related to humans – that is, on the human divide of the evolutionary tree since human and chimpanzee ancestors branched off from a common ancestor sometime between 6 and 8 million years ago.)

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Organisms and Environmental Change:

All organisms encounter some amount of environmental change. Some changes occur over a short time, and may be cyclical, such as daily or seasonal variations in the amount of temperature, light, and precipitation. On longer time scales, hominins experienced large-scale shifts in temperature and precipitation that, in turn, caused vast changes in vegetation – shifts from grasslands and shrub lands to woodlands and forests, and also from cold to warm climates. Hominin environments were also altered by tectonics – earthquakes and uplift, such as the rise in elevation of the Tibetan Plateau, which changed rainfall patterns in northern China and altered the topography of a wide region. Tectonic activity can change the location and size of lakes and rivers. Volcanic eruptions and forest fires also altered the availability of food, water, shelter, and other resources. Unlike seasonal or daily shifts, the effects of many of these changes lasted for many years, and were unexpected to hominins and other organisms, raising the level of instability and uncertainty in their survival conditions.

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Many organisms have habitat preferences, such as particular types of vegetation (grassland versus forests), or preferred temperature and precipitation ranges. When there’s a change in an animal’s preferred habitat, they can either move and track their favored habitat or adapt by genetic change to the new habitat.  Otherwise, they become extinct. Another possibility, though, is for the adaptability of a population to increase – that is, the potential to adjust to new and changing environments. The ability to adjust to a variety of different habitats and environments is a characteristic of humans.

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Figure above shows three possible outcomes of population evolution in environmental dynamics typical of the Plio-Pleistocene. The ability to move and track habitat change geographically (narrow lines) or to expand the degree of adaptive versatility is important for any lineage to persist. Extinction occurs if species populations have specific dietary/habitat adaptations (i.e., a narrow band of ‘adaptive versatility’; highlighted bands) and cannot relocate to a favored habitat. In the hypothetical situation (right band) where adaptive versatility expands, migration and dispersal may occur independently of the timing and direction of environmental change. The evolution of adaptive versatility is the impetus behind the variability selection idea discussed in following paragraphs.

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Earth’s climate has always been in a state of flux. Ever since our ancestors branched off the primate evolutionary tree millions of years ago, the planet has faced drastic swings between moist and dry periods, as well as long-lived glacial freezes and thaws. It’s clear that early humans were able to survive such changes—our existence confirms their success. But a growing number of scientists think that major climate shifts may have also forged some of the defining traits of humanity. In particular, a few large evolutionary leaps, such as bigger brains and complex tool use, seem to coincide with significant climate change. The data is also helping scientists sift through the possible theories for just how climate might have triggered evolutionary advances. For instance, one idea is that big leaps forward were not driven by adaptation to a specific habitat change, but by a series of frequent changes. In other words, humans evolved to live with uncertainty. Rick Potts at the Smithsonian Institution’s Human Origins Program calls this idea “variability selection”, and it’s possible at least two major evolutionary events can be linked to periods of climate instability. Roughly between 3 and 2.5 million years ago, the lineage of ‘Lucy’ [Australopithecus afarensis] became extinct and the first members of our own genus, Homo, appeared. The first simple stone tools also appeared with those fossils, which featured some modern traits like bigger brains. Then, between 2 million and 1.5 million years ago, we see Homo erectus. That bigger-brained hominin had a skeleton very much like our own, more sophisticated tools like double-bladed axes and new behaviors that led early humans out of Africa for the first time. Both of these events happened at times when the local climate was undergoing dramatic shifts. We know, for instance, that some 3 million years ago—around the time the first Homo species appeared—Africa was switching from wooded areas to open grasslands as the climate dried out. This straightforward change in scenery may be part of why early humans evolved away from climbing and toward walking upright. But recent evidence collected from the seafloor gives an even more detailed look at the climate change during this period.

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Variability selection:

Dr. Rick Potts developed the variability selection hypothesis of human origins, linking key human traits to a process of adaptation to climate variability and uncertainty.

Variability selection is a form of natural selection that explains adaptation as a response to dramatically increased variability in the environment. When climate and other aspects of the environment vary dramatically, it can really affect the survival and success of an organism and its offspring over time. The effects can be evident in the gene pool and adaptations of an organism over time. Ultimately, organisms that can cope with widely varying conditions have a better chance of surviving novel and unpredictable environments.

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For many years, the tradition among paleoanthropologists was to try to find the selective environment that drove human evolution, key traits such as walking upright, tool use, larger brains, language, complex innovations. For a long time, the favored explanation was the savanna hypothesis: the drying out of Africa meant that early humans found themselves in arid grassland, and generation after generation there was pressure to adapt to that drying trend. Paleoanthropologists long suspected that human evolution occurred primarily in grassland environments. Variability selection offers a different explanation. Over time and in different places where our ancestors lived, environments varied widely. Variability selection proposes that major features of human evolution were actually ways that our ancestors became more adaptable. It’s a process of selection and adaptation to environmental variability, and it accounts for traits that cannot be explained by adaptation to any one environment or trend. For example, our large brains are useful for processing a wide range of information, our teeth and ability to make tools are useful for consuming a wide variety of foods, our sociability helps us team up with others when our survival is threatened.

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Individual animals do not evolve biologically. They can show a certain capacity to adjust to a changing environment. But the evolution of that capacity—the adaptability of the organism—evolves in a population over time. Sexual reproduction allows DNA to be remixed every generation, creating slightly different genetic makeups to be “tested” against the environment. If these new genomes allowed individuals greater flexibility in nutrition or behavior, they would, according to the variability section hypothesis, provide a survival advantage in new or variable environments. Even if the advantages were small, over many generations the genetic makeups that favored them would become widespread. So, variability selection is a process where combinations of interacting genes, and the genes that enable flexible interactions with the environment, are favored. This process promotes adaptability. The idea of variability selection is that the evolution of adaptability can’t take place in an animal’s lifetime, or in a relatively stable or directionally changing environment. Rather the genetic changes that yield flexible environmental responses are built up in eras of instability in the surroundings. Natural selection was not always a matter of ‘survival of the fittest’ but also survival of those most adaptable to changing surroundings.

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The link between human evolution and climate change:

The basic premise is that large-scale shifts in climate alter the ecological structure and resource availability of a given setting, which leads to selection pressures. Indeed, some of the larger climate shifts in Earth history were accompanied by unusually high rates of faunal turnover—bursts of biotic extinction, speciation, and innovation. For example, a large turnover event occurred near 34 million years ago (Ma) when Earth cooled abruptly and large glaciers first expanded upon Antarctica. Many of the taxa that appeared after 34 Ma were better adapted to the new environments that emerged, which included cooler polar regions, greater seasonality, and arid grasslands. Notable hominin extinction, speciation, and behavioral events appear to be associated with changes in African climate in the past 5 million years.

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Changes to past climates and environments have been linked with certain major events in human evolution. For example, three million years ago an Ice Age began which produced a worldwide trend toward cooler, drier climates. In east Africa, this climate change brought about changes to the local environments in which broad expanses of woodland were replaced by grassland. This environmental change probably resulted in physical and behavioural changes by some species as they adapted to the new conditions. Soon after this environmental change, the first human fossils (genus Homo) and manufactured stone tools appeared in east Africa.

This graph shows milestones in human evolution correlated with climate variability. Milestones indicated along the bottom of the graph show hominin origins; habitual bipedality; first stone toolmaking, eating meat/marrow from large animals; onset of long-endurance mobility; onset of rapid brain enlargement; and expansion of symbolic expression, innovation, and cultural diversity.

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Climate variability during the Neogene is expressed on various timescales, each of which may have been important for hominin evolution. Over the longest timescales, climate trends over millions of years—the global cooling trend and the growth of polar ice sheets—set the stage for the overall evolution of hominins. On shorter timescales, Earth orbital (Milankovitch) processes were critical for controlling aridification cycles in Africa, which could have influenced hominin distribution, adaptation, and local water resource availability. And at millennial and shorter timescales, abrupt climate events could have influenced the demography of individual hominin populations, local extinctions, and population distribution around water resources. Each of these timescales is considered below.

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Paleobiological context of human evolution vis-à-vis climate change:

An important contribution to understanding how human evolution might have been affected by climate and/or habitat change is provided by the other biota that existed both with hominins and apart from them. As climate altered vegetation habitats (determined by rainfall, evapotranspiration, soils, and other aspects of the earth system), this habitat modification applied selective pressures on the fauna that used these habitats, leading to new adaptations, speciation, or extinction. The adaptations that are evident in the faunal assemblages recovered with hominins provide a valuable line of evidence that can be used to reconstruct paleoenvironments and track environmental change.

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Climate events and human evolution correlation chronology:

The major features of human evolution and the major features of Earth’s climatic evolution over the past 8 million years can be integrated to form a chronological summary, summarized in Table below.

Interval Climate Events Sea-Level Events Tectonic Events Hominin Evolutionary Events Archaeological Record Events Fossil Record Events (other than hominins)
8-4 Ma
  • 7-4 Ma: Overall global cooling trend.
  • ~7-4 Ma formation of Greenland Ice Sheet and accompanying drop in global atmospheric CO2 concentrations.
  • 8-5 Ma: Global expansion of C4 vegetation.
  • ~7-5 Ma: Messinian salinity crisis; desiccation of Mediterranean.
  • <8 Ma: Expansion of western rift, uplift of rift shoulders, regional rain shadows and aridification.
  • ~7 Ma: Chimpanzee-hominin split; development of bipedal locomotion.
  • First Australopithecus.
  • Plants and animals show length of the dry seasons increased by many months in the middle to late Miocene, and then shortened again near the Mio-Pliocene boundary.
  • ~8-7 Ma: Fauna indicates cooler conditions in Kenya/Ethiopia.
  • Heterogeneous landscapes but trending towards drier at Mio-Pliocene boundary.
  • Fauna indicates closed habitats at many hominin sites; biogeographic exchange across Mediterranean during Messinian drying.
4-2 Ma
  • 4-3 Ma: Pliocene warming interval and higher CO2 concentrations, humid conditions in East Africa, and weak zonal and meridional sea surface temperature (SST) gradients.
  • 3.6-3.4 Ma: Lake phase in NE Africa.
  • Onset of major Northern Hemisphere glaciation between 3.2-2.6 Ma and development of arid conditions in East Africa.
  • 3-2 Ma: Development of strong sea surface temperature gradients in equatorial Atlantic and Indian Oceans.
  • More seasonally-contrasted, cooler, and drier—and perhaps more variable—climate in North Africa.
  • ~2.8 Ma: Increase in eolian dust fluxes around North Africa.
  • After 2.8 Ma: Expanded amplitudes of North African wet-dry cycles.
  • 2.7-2.5 Ma: Deep lake phase in NE Africa.
  • By 1.8 ma: Disappearance of persistent El-Niño like conditions in tropical Pacific.
  • 2.8 Ma: Growth of polar ice sheets and lowered sea level, onset of glacial/interglacial cycles.
  • Trend for Australopithecus to have larger and taller cheek teeth, reduction of canines, and to maintain a high level of sexual dimorphism.
  • ~ 3-2.4 Ma: Split between australopithecines and Homo.
  • ~2.7 Ma: Evolution of Paranthropus.
  • ~1.8 Ma: Evolution of more carnivorous H. erectus.
  • Australopithecus species disappeared from East African record.
  • 2.58-2.52 Ma: Earliest stone tools.
  • After 2.3 Ma: Stone tools increasingly common.
  • Australopithecines initially associated with fauna that indicates woodland with some grassland or more bushland habitats; first appearance of Equus in Africa and connections with Eurasia grassland expansion, which is coupled with increased body size in Homo.
2-0.5 Ma
  • 1.9-1.7 Ma: Lake phase in NE Africa.
  • 1.8-1.6 Ma: Development of modern tropical global SST gradients.
  • 1.8-1.6 Ma: Greatest expansion of C4 vegetation in East Africa.
  • ~1 Ma: Enhanced amplitude glacial aridity cycles and shift to 100-ky cyclicity.
  • Paranthropus widespread but goes extinct ~1.2 Ma. New species of Homo with smaller cheek teeth, larger brains, and more sophisticated tools, the extinction of others, and substantial improvements in technology. The first dispersal of Homo out of Africa into Eurasia.
  • ~1.6 Ma: Acheulean stone tool technology.
  • 790 ka: Oldest definite evidence of controlled fire.
  • 1.8 to ~1.0 Ma: African fauna indicate fairly open, grassland habitats.
0.5-0.0 Ma
  • Coldest glacial MIS-6 about time of first H. sapiens.
  • ~140-70 ka: Tropical/subtropical megadroughts.
  • Very low sea level during MIS-6 and MIS-2.
  • ~500 ka: First archaic Homo with substantially enlarged brain size.
  • H. heidelbergensis in Europe, Asia, and Africa beginning at about 400 ka. H. erectus expansion into northern latitude climates within
  • Between 200-60 ka: Evolution of Middle Stone Age innovations.
  • ~400 ka: Oldest thrusting spears known.

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If we are all related, why don’t we look the same?

Skin colour, hair, shape of the face and eyes are again determined by climate.

The most obvious physical difference between peoples of Eurasia is their skin colour, which tends to be darker in the sunnier tropical regions. This is no coincidence. Skin darkness, which depends on the pigment melanin, is controlled by a number of poorly understood genes and is also under evolutionary control. For those who live in tropical and subtropical regions, the risk of burns, blistering, and the likelihood of death from skin cancer induced by ultraviolet light is dramatically reduced by having dark skin. There are other, less dramatic advantages: for example, the melanin in pigmented skin allows it to radiate excess heat efficiently, as well as protecting against the destruction of folic acid, an essential vitamin. So in sunny climes, over many generations, people with dark skin live on average longer and have more successful families. In North Asia (i.e. Asia north of the Tibet-Qinghai Plateau and east of the Urals) and Europe there is less sun and a lower risk of skin cancer, but there is the ever-present risk of rickets, a bone disease caused by lack of sunlight that was still killing London children even at the beginning of the twentieth century. So there are at least two evolutionary selection forces working in concert, tending to grade skin colour according to latitude. The sun-driven change in skin and hair colour evolves over many generations. From the available genetic evidence, Africans appear always to have been under intense selective pressure to remain dark-skinned. Outside Africa, though, we can see gradations of skin and hair colour as we move from Scandinavia in the north of Europe and Siberia in the north of Asia down to Italy and Southeast Asia in the south of those regions. The darkest-skinned groups of non-Africans still tend to live in sunny and tropical countries. Clearly, if change in skin colour takes many generations, we shall sometimes find people whose recent ancestors have moved to live in sunny countries and who are still fair skinned (and vice versa). A good example is Australia, a sunny country where the majority of today’s inhabitants are pale-skinned descendants of recent immigrants. Australia has one of the world’s highest rates of skin cancer, and this has already started it on the slow evolutionary path that will eventually lead to descendants of Europeans becoming generally darker-skinned. Conversely, the first visitors to the north of Europe and Asia probably started their journeys looking very dark skinned and evolved to become paler later. Apart from exceptions such as Australia, the average skin colour around the world is thus tuned to the relative amount of ultraviolet light.

Other, more solid differences, such as the shape of our face, are determined by the underlying skull bones. These do vary between different parts of East, Southeast, and South Asia, and imply a rather long period of separation between the populations of these regions. Throughout East Asia we see the Mongoloid type with an extra, so-called epicanthic fold protecting the upper eyelid, and broad cheeks and skull. This type is often further divided into Northern Mongoloid and Southern Mongoloid, with the latter showing a less marked eye-fold and including southern Chinese and darker-skinned Mongoloid types in Southeast Asia. A great variety of peoples is found in South Asia, particularly in India. The majority of Indians, although dark skinned, are more similar physically to Europeans and Middle Easterners than they are to East Asians. Europeans, with their long, narrow heads, round eyes, and pale skin are sometimes called Caucasian. The farther north in India and Pakistan we go, the closer is the physical resemblance to ‘Caucasoid’ Levantines and Middle Easterners. In southern India, darker-skinned, curly haired, round-eyed peoples predominate. In eastern India, Assam, and Nepal there are peoples with a more Mongoloid appearance.

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Microbial survival:

Throughout evolution, humans, like all mammalian species, have maintained an intimate relationship with the microbial world. We have survived thanks to the efficient defense mechanisms we have developed against potentially dangerous micro-organisms. Pathogenic micro-organisms are still here because they have found ways of avoiding elimination by the host or by the microbial competition. Successful pathogens have developed strategies to enter the body, and reach and colonize their favorite niche, while defying the powerful human immune system.

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Viruses are dominant drivers of human evolution a 2018 study:

In a new study, published in the eLife scientific review, researchers describe the application of large data analyzes to reveal the full extent of influencing viruses in human and other mammalian development. The findings of the study show that 30 percent of all protein adjustments since the time of humans deviating from the chimpanzees have been driven by the viruses. When an environmental change occurs, species are able to adapt to change due to mutations in their DNA. Although these mutations occur accidentally, some of them make the body better adapted to its new environment. These are known as adaptive mutations. Over the last decade, scientists have discovered a large number of adaptive mutations in a wide variety of locations in the genome of humans and other mammals. The fact that adaptive mutations are so diffused is a mystery. What kind of environmental pressure could potentially lead to so much adaptation to so many points of the genome? Viruses are ideal candidates as they are always present, constantly changing and interacting with hundreds of thousands of proteins. When we have a pandemic or epidemic at some point in the evolution, the population targeted by the virus either adapts or disappears.

The first step in the study was to identify all proteins that are known to interact naturally with viruses. After analyzing tens of thousands of scientific publications, they came up with a list of 1,256 proteins. The next step was to construct large data algorithms to define genomic databases and compare the evolution of proteins that interact with viruses with that of other proteins. The results of their analysis revealed that adaptations have occurred three times more frequently in proteins that interact with viruses than other proteins. This discovery that this battle with viruses has shaped us in all respects is profound. All organisms have been living with viruses for billions of years. The new study shows that these interactions have affected every part of the cells. Viruses eclipse almost every function of the cells of an organism host in order to reproduce and spread them, so it makes sense to drive the evolution of the cellular mechanism to a greater extent than other evolutionary pressures such as predation or environmental conditions. The study also sheds light on some long-term biological mysteries, as closely related species have evolved different mechanisms that perform identical cellular functions, such as DNA replication or membrane production.

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Evolution of behavioural modernity, emotion, language and morality:

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Behavioral modernity:

Behavioral modernity is a suite of behavioral and cognitive traits that distinguishes current Homo sapiens from other anatomically modern humans, hominins, and primates. Although often debated, most scholars agree that modern human behavior can be characterized by abstract thinking, planning depth, symbolic behavior (e.g., art, ornamentation, music), exploitation of large game, and blade technology, among others. Underlying these behaviors and technological innovations are cognitive and cultural foundations that have been documented experimentally and ethnographically. Some of these human universal patterns are cumulative cultural adaptation, social norms, language, and extensive help and cooperation beyond close kin. It has been argued that the development of these modern behavioral traits, in combination with the climatic conditions of the Last Glacial Maximum, was largely responsible for the human replacement of Neanderthals and the peopling of the rest of the world.

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Transition to behavioral modernity:

Until about 50,000–40,000 years ago, the use of stone tools seems to have progressed stepwise. Each phase (H. habilis, H. ergaster, H. neanderthalensis) started at a higher level than the previous one, but after each phase started, further development was slow. Currently paleoanthropologists are debating whether these Homo species possessed some or many of the cultural and behavioral traits associated with modern humans such as language, complex symbolic thinking, technological creativity etc. It seems that they were culturally conservative maintaining simple technologies and foraging patterns over very long periods. Around 50,000 BP, modern human culture started to evolve more rapidly. The transition to behavioral modernity has been characterized by most as a Eurasian “Great Leap Forward”, or as the “Upper Palaeolithic Revolution”, due to the sudden appearance of distinctive signs of modern behavior and big game hunting in the archaeological record. Some other scholars consider the transition to have been more gradual, noting that some features had already appeared among archaic African Homo sapiens since 200,000 years ago. Recent evidence suggests that the Australian Aboriginal population separated from the African population 75,000 years ago, and that they made a sea journey of up to 160 km 60,000 years ago, which may diminish the evidence of the Upper Paleolithic Revolution.

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Modern humans started burying their dead, using animal hides to make clothing, hunting with more sophisticated techniques (such as using trapping pits or driving animals off cliffs), and engaging in cave painting. As human culture advanced, different populations of humans introduced novelty to existing technologies: artifacts such as fish hooks, buttons, and bone needles show signs of variation among different populations of humans, something that had not been seen in human cultures prior to 50,000 BP. Typically, H. neanderthalensis populations do not vary in their technologies, although the Chatelperronian assemblages have been found to be Neanderthal innovations produced as a result of exposure to the Homo sapiens Aurignacian technologies.

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Among concrete examples of modern human behavior, anthropologists include specialization of tools, use of jewellery and images (such as cave drawings), organization of living space, rituals (for example, burials with grave gifts), specialized hunting techniques, exploration of less hospitable geographical areas, and barter trade networks. Debate continues as to whether a “revolution” led to modern humans (“the big bang of human consciousness”), or whether the evolution was more “gradual”.

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Archaeologically, a number of empirical traits have been used as indicators of modern human behavior. While these are often debated a few are generally agreed upon. Archaeological evidence of behavioral modernity includes:

  • burial
  • fishing
  • figurative art (cave paintings, petroglyphs, dendroglyphs, figurines)
  • systematic use of pigment (such as ochre) and jewellery for decoration or self-ornamentation
  • Using bone material for tools
  • Transport of resources over long distances
  • Blade technology
  • Diversity, standardization, and regionally distinct artifacts
  • Hearths
  • Composite tools

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The Evolution of Human Emotions:

One question that is, surprisingly, hardly ever asked is this: Why do humans have the capacity to experience, express, and read in others such a wide variety of emotional valences? It is just assumed that humans are emotional, but the question of “why” is left unanswered. One can find somewhat vague pronouncements that emotions are socially constructed, and with big brains came language and culture that allow for an expanded palate of emotions. But is this really the answer? No, because emotions are generated in the subcortical regions of the brain, not in the neocortex. True, culture gives us the capacity to label emotions, and this comes from the neocortex, but the emotions themselves are of deeper origins, not only in the actual structure of brain but also in its evolution over the last 8 million years.

Many believe that humans construct their reality with their capacities for language and culture. This standard social science model is no longer adequate, however. Humans are animals that evolved like any other animal; and our traits are the consequence of adaptation to various habitats and niches in these habitats by our distant and near primate relatives. To assume that culture explains everything is, in essence, an approach that explains very little. Hominins had had to get organized, or die, long before the neocortex grew much beyond that of a contemporary chimpanzee; and thus, it is inconceivable that the only force regulating social conduct and social organization is cultural. Hominins had to get organized without the benefit of culture; and the only hard evidence about how they did so is in the wiring of human brain when compared to the brain of a chimpanzee or any great ape. The differences in subcortical areas of the brain and in the level of connectivity between the subcortex and neocortex are the “smoking gun” of what natural selection did, long before culture evolved as a consequence of natural selection late in hominin development. If we know how the brain became rewired, what the selection pressures were that drove this rewiring, and how emotionality interacts with other hard-wired behavioral propensities of our closest relatives, we have a pretty good idea of how emotions evolved but, equally important, we have much more understanding of how they operate among humans in the present, and what the neurological mechanisms driving this operation are.

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The first work to be done on emotions from an evolutionary standpoint was done by our friend Charles Darwin. His work titled, The Expressions of the Emotions in Man and Animals, was really the seminal work on the subject of emotions. The book, first published in 1872 was an immediate bestseller, and an immediate controversy. In it, Darwin, using accepted physiological and psychological theories, explained the reasons behind movements and expressions, and thus the emotions that are behind them. He proposed three principles to explain the “chief expressive actions” in humans and other animals.

The first is what he referred to as “serviceable associated habits”. If, under a certain circumstance, an animal behaves in a way that gratifies it a desire, or takes away some sensation, it will behave in a similar way when confronted with a similar circumstance. A good example of this principle is in the case of a dog preparing to lie down. In the dog’s natural surroundings (i.e. in brush or woodland), it would circle around the spot it intended to lie down in and maybe scratch at it a few times to push aside branches and then to remove uncomfortable stones or branches. Because this action gave the dog a more comfortable spot, and thus better sleep, the action is performed routinely before sleeping, regardless of whether the dog is in the forest or on the carpet in a home.

The second principle, “The Principle of Antithesis”, stated that an animal, if confronted with a situation opposite the original, would perform a movement that is accordingly opposite. For this principle, a very interesting example was given. Darwin describes a dog and a cat in two emotional states. When affectionate, the dog’s torso is down, its butt is in the air, and its tail is wagging or down. The cat, on the other hand, stands erect, with its back maybe slightly arched, its tail still and upright, and its ears pointed. The positions are opposite of those in which the animals are aggressive. When aggressive, the dog’s body is erect, its head is held back, its hair is bristling, and its tail is stiff. The cat, accordingly, crouches low to the ground, its ears become flat against the head, and its tail whips back and forth. Thus, Darwin concluded that when the animal is trying to display affection, its position is as far from the position of aggression as possible.

The third principle, which Darwin titled as “The principle of actions due to the constitution of the Nervous System, independently from free will, and independently to a certain extent of Habit” , states that some motions (such as trembling under fear) are solely a physiological reaction, and have nothing to do with free will. They are involuntary nerve reactions that in some cases may have been developed, and in others are “side effects” of other physiological programs. Trembling with fear does the subject no good, and in fact could slow it down or render incapable of performing life-promoting tasks, thus it could not have been acquired through habit. Sometimes it was possible to trace the developed nerve reactions to an action acquired through habit. An example of this is the case of an infant tightly shutting its eyes when upset. “This is quite involuntary, and does not occur later in life, but the whole mechanism by which it is produced has been traced out, and it is found that it is a provision to prevent injury to the delicate vessels of the eyes by the increased flow of blood to the head during violent screaming,”.

Darwin’s assertions immediately provoked criticism and dispute, especially in regard to the first principle. What made the first principle so controversial was his claim that the actions acquired through habit were hereditary; “. . . some actions, which were at first performed consciously, have become through habit and association converted into reflex actions, and are now so firmly fixed and inherited. . .,”. There grew a giant rift in the study of emotions between those taking the Nativist approach; usually supporting the genetic approach to emotion originated by Darwin, and those taking the equisitionist approach to human nature, emphasizing the importance of learning over heredity. The two sides of the argument have many titles, including, respectively, nature versus nurture, and biosocial versus constructivist.

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The psychology side of the evolutionary psychological approach to the emotions is largely centered on the theories of several American psychologists. The first of these was William James. According to James, “Instinctive reactions and emotional expressions thus shade imperceptibly into each other. Every object that excites an instinct excites an emotion as well,”. In other words James proposed that a stimulus from the outside environment would create an internal physiological reaction as well as an external reaction/expression. Thus, emotion is the feeling of both the physiological and behavioral processes. Several years later, a Danish physician by the name of Carl Lange constricted James’ original theory to state that emotion is simply the perception of physiological changes taking place internally. The two theorists were clumped together, and their ideas are referred to as the James-Lange theory. Much like Darwin’s claims, the James-Lange theory faced serious criticism. Walter B. Cannon published research on animals whose internal organs were separated from the nervous system yet continued to display emotional expression. These three scientists’ theories form the basis of the psychological view of the emotions. To date, the standard evolutionary psychological approach to the emotions is a combination of the theories of the founders of the field and subsequent theorists and experiments. In general evolutionary theory it is accepted that repeated encounters with similar situations were met with varying actions. Certain actions promoted life, and certain actions promoted death. Thus everything in the mind is “program” designed to solve a specific problem encountered numerous times throughout evolutionary history. These programs are triggered by events in the outside environment.

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But what if the environment triggered the ‘sleep program’ (i.e. the sun went down, its dark and cold) at the same time that a predator came on the scene triggering the ‘run away program’? This is an example of two conflicting adaptive programs. The solution to this problem is that the mind was equipped with ‘governing programs’ that had the authority to override certain programs when others were activated. So when the environment triggered the ‘run away’ program, the governing programs would shut down the ‘sleep program’. Not only would they shut down some programs, but these governing programs, known as superordinate programs would activate and orchestrate a multitude of programs (adrenaline levels rise, heart rate rises, hearing becomes sharper). These governing, or super ordinate programs are the emotions. Just like the sub-programs, they were evolved through a process of repeated encounters, with varying results that determined their success or failure. The emotions affect sub-programs by activating them, deactivating them, or adjusting their parameters so that they all coordinated in confronting the situation . Generally speaking, the situations where emotions play a role are those that recurred ancestrally, those that could not be dealt with without a governing program (emotions are not needed in situations where independent programs solved independent problems), and those “in which an error would have resulted in large fitness costs,”.

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A standard example of an ancestrally recurrent situation where emotion was developed as an adaptive process is being alone at night and hearing a sound. The emotion is fear: ‘I am being stalked’. The super ordinate programs in the brain activate the subprograms. First, shifts in perception and attention take place: Hearing becomes more acute, motion is more detectable, and less evidence is required before acting. Next, priorities change: Tiredness is put aside by physiological processes, hunger is forgotten, any anxieties experienced during the day are also forgotten, and pain sensory systems are dampened. Then information-gathering programs are redirected: Finding a place to sleep or food are no longer important, so finding help or refuge become priorities. After this, conceptual frames change: things normally considered safe become labelled “dangerous”, Memory is redirected: not only everything in the present situation looks suspicious but certain memories previously insignificant become clues, inference systems are activated: i.e. whatever you see, you know, learning systems are activated, physiology changes: blood is redirected, adrenalin is secreted, heart rate goes up, etc, decision-making becomes more automatic. The example of fear is a good one because the scenario that our ancestors faced (being stalked by a wild animal) is similar to the scenario today of being stalked by a stranger who could be a robber, rapist or murderer. This example highlights the major beliefs of evolutionary psychologists in regard to emotions. Generally speaking, according to evolutionary psychologists, emotions are adaptive programs designed through repeated encounters that are intended to either direct other physiological programs or to directly solve adaptive problems faced by a species over time.

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Emotions are universal. Regardless of age, gender, or culture emotions remain constant. The interplay between belief and fact, innate ideas and science, suspicion and proof, between what is inside our brains, and what is part of the outside environment exists in every aspect of humankind’s experience in the world. This is an interplay that makes all science interesting, and difficult to evaluate.

“Feelings are not supposed to be logical. Dangerous is the man who has rationalized his emotions.”

-David Borenstein

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Paul Ekman is most noted in this field for conducting research involving facial expressions of emotions. His work provided data to back up Darwin’s ideas about universality of facial expressions, even across cultures. He conducted research by showing photographs exhibiting expressions of basic emotion to people and asking them to identify what emotion was being expressed. In 1971, Ekman and Wallace Friesen presented to people in a preliterate culture a story involving a certain emotion, along with photographs of specific facial expressions. The photographs had been previously used in studies using subjects from Western cultures. When asked to choose, from two or three photographs, the emotion being expressed in the story, the preliterate subjects’ choices matched those of the Western subjects most of the time. These results indicated that certain expressions are universally associated with particular emotions, even in instances in which the people had little or no exposure to Western culture. The only emotions the preliterate people found hard to distinguish between were fear and surprise. Ekman noted that while universal expressions do not necessarily prove Darwin’s theory that they evolved, they do provide strong evidence of the possibility. He mentioned the similarities between human expressions and those of other primates, as well as an overall universality of certain expressions to back up Darwin’s ideas. The expressions of emotion that Ekman noted as most universal based on research are: anger, fear, disgust, sadness, and enjoyment.

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In sum, basic tendencies to detect and respond to significant events are present in the simplest single cell organisms, and persist throughout all invertebrates and vertebrates. Within vertebrates, the overall brain plan is highly conserved, though differences in size and complexity also exist. The forebrain differs the most between mammals and other vertebrates, though the old notion that the evolution of mammals led to radical changes such that new forebrain structures were added has not held up. Thus, the idea that mammalian evolution is characterized by the addition of a limbic system (devoted to emotion) and a neocortex (devoted to cognition) is flawed. Modern efforts to understand the brain mechanisms of emotion have made more progress by focusing on specific emotion systems, like the fear or defense system, rather than on efforts to find a single brain system devoted to emotion. Also, progress has been made in animal studies by focusing on emotion in terms of brain circuits that contribute to behaviors related to survival functions.

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Evolution of morality:

The evolution of morality refers to the emergence of human moral behavior over the course of human evolution. Morality can be defined as a system of ideas about right and wrong conduct. In everyday life, morality is typically associated with human behavior and not much thought is given to the social conducts of other creatures. Nearly 150 years ago, Charles Darwin proposed that morality was a by-product of evolution, a human trait that arose as natural selection shaped man into a highly social species—and the capacity for morality, he argued, lay in small, subtle differences between us and our closest animal relatives. “The difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind,” he wrote in his 1871 book The Descent of Man. Is morality an adaptation, crafted by the invisible hand of natural selection? Or do we just make it up? This turns out to be a tricky question to answer. On the one hand, there’s little doubt that evolutionary theory can shed light on the origins of some of the behaviours that fall within the rubric of morality, including altruism, empathy, and our characteristic attitudes about certain kinds of sexual behaviour. On the other hand, the morality-as-adaptation hypothesis faces some serious challenges. If morality were a direct product of evolution, why would people constantly argue about what’s right and wrong? Why would we spend so much time teaching our children to be good, and inculcating in them virtues such as generosity? Why would we experience inner conflict between what we think is morally right and what we really want to do? Moral thinking pervades our practical lives, but where did this way of thinking come from, and what purpose does it serve? Is it to be explained by environmental pressures on our ancestors a million years ago, or is it a cultural invention of more recent origin?

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There are at least two reasons to think morality bears the imprint of our evolutionary history. The first comes from observations of a class of individuals that psychologists all too often ignore: other animals. Nonhuman animals obviously don’t reason explicitly about right and wrong, but they do exhibit some aspects of human morality. Rather than being locked into an eternal war of all-against-all, many animals display tendencies that we count among our most noble: They cooperate; they help one another; they share resources; they love their offspring. For those who doubt that human morality has evolutionary underpinnings, the existence of these ‘noble’ traits in other animals poses a serious challenge. When speaking of other species, we inevitably explain these traits in evolutionary terms. No one would want to explain the fact that female dogs love and care for their puppies as an arbitrary product of canine culture, for example. Given that we accept an evolutionary explanation for this behaviour in other species, it seems tenuous to argue that the same behaviour in human beings is entirely a product of a completely different cause: learning or culture. That’s one reason to accept that evolutionary theory has a role to play in the analysis of moral behaviour.

A second is that, not only do we know that these kinds of behaviour are part of the standard behavioural repertoire of humans in all culture and of other animals, we now have a pretty impressive arsenal of theories explaining how such behaviour evolved. Kin selection theory explains why many animals – humans included – are more altruistic toward kin than non-kin: Kin are more likely than chance to share any genes contributing to this nepotistic tendency. Reciprocal altruism theory explains how altruism can evolve even among non-relatives: Helping others can benefit the helper, as long as there’s a sufficient probability that the help will be reciprocated and as long as people avoid helping those who don’t return the favour. Another promising theory is that altruism is a costly display of fitness, which makes the altruist more attractive as a mate or ally. Overall, the evolutionary explanation of altruism represents one of the real success stories of the evolutionary approach to psychology.

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For the last 30 years, the psychologist Michael Tomasello has been trying to determine how our species’ social nature gave rise to morality. The co-director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, Tomasello has spent much of his career conducting experiments that compare the social and cognitive abilities of chimpanzees, our closest relative in the animal kingdom, and human toddlers. In his book A Natural History of Human Morality, he draws on decades’ worth of work to argue for the idea that humans’ morality, unique in the animal kingdom, is a consequence of our tendency to collaborate and cooperate in ways that other great apes do not. Beginning in the early 20th century, research on non-human primates—like chimpanzees, bonobos, and orangutans—has shown that they are capable of many things once considered uniquely human, like tool-making, empathy, discerning the intentions and goals of others, and forming friendships. But humans also have language, laws, institutions, and culture. For a long time, the dominant explanation for these uniquely human concepts was our raw intelligence—the human brain is three times larger than the chimpanzee brain—but in recent years, some scientists have also argued that our more social nature may be what’s allowed us to advance so much further than the apes. But as Tomasello argues in his book, this “social intelligence hypothesis” is something of an understatement. A social nature isn’t enough to fully distinguish between humans and chimpanzees—male chimpanzees can form political alliances, for example, and sometimes work together to hunt, both of which require advanced social skills. Humans are not just socially intelligent, then; as Tomasello and others have put it, we’re “ultra-social” in ways that the great apes are not, with an enhanced capacity for cooperation that arose somewhere along our species’ evolutionary path.

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Tomasello has conducted dozens of studies to support this idea. In one study published in 2007, he and his colleagues gave 105 human toddlers, 106 chimpanzees, and 32 orangutans a battery of tests assessing their cognitive abilities in two domains: physical and social. The researchers found that the children and the apes performed identically on the physical tasks, like using a stick to retrieve food that was out of reach or recalling which cup had food in it. But with the social tests—like learning how to solve a problem by imitating another person, or following an experimenter’s gaze to find a treat—the toddlers performed about twice as well as the apes. Related to this enhanced social ability is a greater tendency to work together, even on tasks where collaboration isn’t necessary. In a 2011 study by Tomasello and his Planck Institute colleagues, 3-year-old children and chimpanzees were given an opportunity to obtain a reward either on their own or by collaborating with another member of their species. The experiment was set up so that the children and the apes knew a) that they would get the reward regardless of whether they worked with a partner, and b) that working with a partner would mean both of them got the same reward. Children, the researchers found, were much more likely to collaborate than chimpanzees.

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There are many theories for why humans became ultra-social. Tomasello subscribes to the idea that it’s at least partly a consequence of the way early humans fed themselves. After humans and chimpanzees diverged from their common ancestor around 6-7 million years ago, the two species adopted very different strategies for obtaining food: Chimpanzees, who eat mostly fruit, gather and eat the majority of their food alone; humans, by contrast, became collaborative foragers. The fossil record shows that as early as 400,000 years ago, they were working together to hunt large game, a practice that some researchers believe may have arisen out of necessity—when fruits and vegetables were scarce, early humans could continue the difficult work of foraging and hunting small game on their own, or they could band together to take home the higher reward of an animal with more meat. Chimps show no signs of this ability. “It is inconceivable,” Tomasello has said, “that you would ever see two chimpanzees carrying a log together.” In one of the earliest studies of chimpanzee cooperation, published in 1937, chimpanzees only worked together to pull in a board with food on it after they’d been extensively trained by an experimenter—they showed no natural ability to do it on their own. (Even when chimpanzees do collaborate, there’s been no evidence to date that they have the ability to adopt complementary roles in group efforts or establish a complex division of labor.)

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But collaboration didn’t just change the way early humans procured food, Tomasello argues; it also changed how humans understood themselves in relation to others. Specifically, people came to think of themselves as part of a larger unit whose members worked together for mutual gain. They began, in other words, to have what Tomasello calls “shared intentionality.” This, he says, is the subtle cognitive capacity—that difference of degree Darwin wrote about—that sets humans apart from the great apes, the reason why we have developed cultural institutions and engage in large-scale collaborative activities. Sharing intentions means that two minds are paying attention to the same thing and working toward the same goal, but each with its own perspective on that shared reality. This shared intentionality, Tomasello believes, is the basis of morality. Some psychologists and philosophers break morality into two components: sympathy, or concern for another individual; and fairness, the idea that everyone should get what they deserve. Many animals are capable of the former—a chimpanzee, for example, will behave in altruistic ways, like retrieving an out-of-reach object for another chimp—but only humans, it appears, have a sophisticated understanding of fairness.

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To illustrate this point, Tomasello uses the example of two people working together to pick fruit from a tree: The first person boosts up the second to get to the top of the tree, where he picks fruit for the both of them. The underlying assumption in this interaction is that each person will fulfil the duties of his unique role, and that, once the fruit has been collected, it will be divided fairly. If one person abandoned the task, or gave in to the impulse to take more than his share, the mutual benefit of their partnership would be negated. A similar scenario has played itself out in Tomasello’s lab: In one experiment, pairs of chimpanzees were brought into a room and given the opportunity to work together to get some fruit. When the fruit was already pre-divided into equal portions, both primates took only their share. But when they had to divide it up themselves, the dominant chimpanzee generally took most or all of it. When toddlers were faced with a similar task of collaborating to obtain food or toys, and then dividing up those toys, they generally split them up equally. If the two children each worked separately on the same task, though, and one obtained more toys that the other, the luckier child generally didn’t share with the unluckier one. Through their actions, the researchers concluded, the children in the study seemed to believe that fairness was the equal division of spoils when both parties worked together to obtain them—that sharing was fair only in the context of collaboration.

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In The Descent of Man, Darwin wrote: “I fully subscribe to the judgment of those writers who maintain that of all the differences between man and the lower animals, the moral sense or conscience is by far the most important.” By extension, then, our enhanced ability to cooperate may be the most significant distinction between us and our closest evolutionary relatives.

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Evolution of language:

All animals communicate. However, only humans communicate through language, which can be written, spoken or signed. The enormous benefits of language have allowed us to teach others, pass on our culture, discuss the past and future, and promote social relationships. Scientists look at the skeletons of our ancestors and the archaeological evidence of their behaviour for clues about their language capability, particularly with regards to speech.

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Self-awareness:

The earliest human burials inform us of the adoption of symbolic behaviour. For the first time man possessed an awareness of his own existence, felt anxiety about death and wondered about an afterlife. These concerns once again socialised human groups. Sima de los Huesos (Pit of Bones) at Atapuerca in the province of Burgos shows evidence of the oldest funeral practice. The bottom of a vertical pit there reveals an accumulation of cadavers of Homo heidelbergensis from 300,000 years ago. This is a unique and exceptional case from the Lower Paleolithic Age, contrasting sharply with the large number of burials from the Mid-Paleolithic Age, such as those at Skhul, Qafzeh and Kebara in Israel. The Neanderthals buried their dead close to their own habitat, in very visible tombs and placed in foetal position. The deceased also received a symbolic tribute in the form of an offering.

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Symbol… the beginning of abstract knowledge:

The emergence of symbolic language shows the complexity of the human mind and its capacity for abstraction. Following this first step, language, art and the civilisation would be developed. Primitive works of art had an aesthetic, mystic function, which also promoted social cohesion. Homo sapiens developed a wide variety of artistic forms, such as cave painting, clay modelling, carving and engraving. The oldest known art samples go back 400,000 years and are found in Germany. Made by Homo heidelbergensis, they consist of elephant bones decorated with engraved stripes. The Venus of Berekhat Ram, found in the Near East, dates back 250,000 years. These are two isolated examples, since the artistic phenomenon truly emerged in the Upper Paleolithic Age, which would show the existence of a mankind already organised and structured from a social standpoint. The artistic representations found in the many caves show the evolution of the figurative styles of parietal art and the variation in the representations of natural objects. They also include signs, animals and the progressive introduction of movement, detailism and realism.

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When did language evolve?

Because language cannot ‘fossilise’, scientists have to rely on purely circumstantial evidence when trying to determine the language and speech capabilities of our ancient ancestors. This has led to continued debates as to when language evolved. There are two main views – some scientists believe language appeared suddenly, and is limited to our own species. Others claim language evolved slowly over the last 2 million years and was not restricted to our own species. Those who support a sudden development of language focus on archaeological evidence of behaviour that could be connected to language use. Much of this evidence appears only in the last 40,000 years and includes the manufacture of highly complex tools, the production of symbolic art and the existence of widespread trade systems. By contrast, those who claim language evolved slowly base their argument on skeletal remains and the evidence of structures related to speech production. Certain physical features associated with spoken language, such as the position of the vocal tract, the structure of the brain and the size of the spinal cord, gradually evolved into the modern human form. This evidence is seen to indicate an increasing ability for language and speech over time.

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Looking at some of our ancestors for language evolution:

  1. ‘Lucy’ – Australopithecus afarensis

Date: 2.8 to 3.9 million years ago

Where lived: eastern Africa

Language ability: commonly thought to have no language or speech abilities. It is likely however, that communication was very important and they may have been as vocal as modern chimpanzees.

The base of Lucy’s skull was ape-like in shape. This indicates that she, and others of her species Australopithecus afarensis, had an ape-like vocal tract. Chimpanzees, for instance, have a vocal tract with a high larynx and a short pharynx. This limits the range of sounds that they are able to produce. Lucy’s sound range would probably have been restricted in the same way. The speech of modern humans requires a complex co-ordination of breathing muscles in order to vary pitch and produce long sentences. Lucy’s relatively narrow spinal cord compared to modern humans indicates that she lacked the nerves responsible for this fine control of the muscles that co-ordinate breathing during speech. Language is more than just speech and experiments with chimpanzees show that they are able to learn and understand simple sign language. This has been called ‘protolanguage’ because it lacks the syntax and grammar of modern language. Lucy’s brain was similar in size and structure to a chimpanzee’s so she may have been able to use simple protolanguage.

  1. The Turkana Boy – Homo ergaster

Date: 1.5 -1.9 million years ago

Lived: Africa, possibly migrated out into regions of the Middle East and Asia

Language ability: limited speech and language ability. Probably had advanced communication skills and the capability to produce some simple words and communicate to a greater degree than is seen in our closest living relatives, the chimpanzees. Evidence for this species language ability comes from their fossilised skeletons and from detailed analysis of their tool technology.

It was initially believed that the ‘Turkana Boy’, and members of his species, Homo ergaster, were capable of language. This was because the inside of the boy’s fossilised skull showed an impression from a part of the brain known as Broca’s Area. Possession of Broca’s Area was once considered to indicate the ability to speak. New technologies such as Positron Emission Tomography (PET) have now caused this idea to be revised. PET scans highlight areas of the brain that are active during language activities. They have shown that Broca’s Area does not always function during speech and cannot be used as evidence of speech in our ancestors. The vertebrae in the upper part of the Turkana Boy’s backbone showed that his spinal cord was only about half the size of a modern human’s. The speech of modern humans requires a complex co-ordination of breathing muscles in order to vary pitch and produce long sentences. The Turkana Boy’s narrow spinal cord indicates that he lacked the nerves responsible for this fine control of the muscles that co-ordinate breathing during speech. The tools made by Homo ergaster are known as Mode 2 or Acheulian. They are simple and repetitive in design and could have been learnt through imitating the actions of others rather than by spoken language.

  1. Neanderthals – Homo neanderthalensis

Date: 300,000 – 28,000 years ago

Where lived: Europe and the Middle East

Language ability: relatively advanced language abilities, but evidence suggests that they may have had a limited vocal range compared to modern humans. If this were the case, then their ability to produce complex sounds and sentences would be affected. There has been considerable debate about whether Neanderthals had the capability for fully modern speech. The Neanderthals (Homo neanderthalensis) became extinct about 28,000 years ago and it is often claimed that a reduced language ability compared with modern humans may have been a factor in their extinction. Evidence for and against their language ability is based on analyses of their skeletal remains and the artefacts that they left behind.

Neanderthals left little in the way of symbolic art, an indication that their thought processes, and hence language ability, were unlike that of their modern human contemporaries. Many scientists reached a similar conclusion after comparing Neanderthal vocal tracts to those of modern humans.

The vocal tract’s structure is revealed in the base of the skull. Modern apes, such as chimpanzees, have a flat skull base and a high larynx whereas modern humans have an arched skull base and a low larynx. Our low larynx allows room for an extended pharynx and this structure enables us to produce the wide range of sounds we use in speech. Neanderthal skull bases appear to be less arched than those of modern humans but more arched than those of modern apes. This suggests that the Neanderthals would have been capable of some speech but probably not the complete range of sounds that modern humans produce. The hyoid bone is a small, U-shaped bone that attaches to the larynx at the top of the vocal tract. Fossilised hyoid bones are very rarely found, so this Neanderthal hyoid from Kebara, Israel, was a fascinating discovery. Its similarity to those of modern humans was seen as evidence by some scientists that Neanderthals possessed a modern vocal tract and were therefore capable of fully modern speech. However, recent studies show that hyoid shape is not linked to the structure of the vocal tract. Pig hyoids, for example, are almost identical to those of modern humans.

Researchers studying Neanderthal genes discovered that they shared the same version of a gene FOXP2 with modern humans. FOXP2 is the only gene known so far that plays a key role in language. When mutated, it primarily affects language without affecting other abilities. This gene appears in different forms in other vertebrates where it performs a slightly different function. This suggests the gene mutated not long before the split between the Neanderthals and modern human lines. However, there are plenty of genes involved in language so it takes more than the FOXP2 gene to prove language ability.

  1. Cro-Magnons – Homo sapiens

Date: 40,000 – 10,000 years ago

Where lived: Europe

Language ability: The Cro-Magnons were members of our own species, Homo sapiens. There is little reason to doubt that these people had the ability to talk and use symbolic language. Although Cro-Magnon people have left no evidence of written language, they produced symbolic art, performed long distance trade, held ritual burial ceremonies and planned and designed a technologically advanced tool kit.

The physical features associated with spoken language, such as the vocal tract, the structure of the brain and the size of the spinal cord, are identical between Cro-Magnon people and humans living today. This means that Cro-Magnon people would have been capable of producing the same sounds we use in speech.

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Molecular evolution of FOXP2, a gene involved in speech and language a 2002 study:

Language is a uniquely human trait likely to have been a prerequisite for the development of human culture. The ability to develop articulate speech relies on capabilities, such as fine control of the larynx and mouth, that are absent in chimpanzees and other great apes. FOXP2 is the first gene relevant to the human ability to develop language. A point mutation in FOXP2 co-segregates with a disorder in a family in which half of the members have severe articulation difficulties accompanied by linguistic and grammatical impairment. This gene is disrupted by translocation in an unrelated individual who has a similar disorder. Thus, two functional copies of FOXP2 seem to be required for acquisition of normal spoken language. Authors sequenced the complementary DNAs that encode the FOXP2 protein in the chimpanzee, gorilla, orang-utan, rhesus macaque and mouse, and compared them with the human cDNA. They also investigated intraspecific variation of the human FOXP2 gene. Here they show that human FOXP2 contains changes in amino-acid coding and a pattern of nucleotide polymorphism, which strongly suggest that this gene has been the target of selection during recent human evolution.

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Evolution and Culture:

Within the blink of an eye on a geological timescale, humans advanced from using basic stone tools to examining the rocks on Mars. Our cultural capacities to create new ideas, to communicate and learn from one another, and to form vast social networks together make us uniquely human, but the origins, the mechanisms, and the evolutionary impact of these capacities remain unknown. Researchers have begun to recognize that understanding non-genetic inheritance, including culture, ecology, the microbiome and regulation of gene expression, is fundamental to fully comprehending evolution. It is essential to understand the dynamics of cultural inheritance at different temporal and spatial scales, to uncover the underlying mechanisms that drive these dynamics, and to shed light on their implications for our current theory of evolution as well as for our interpretation and predictions regarding human behavior.

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Human Cultural Evolution:

There are many examples of human cultural evolution. They include: tool making, the controlled use of fire, manufacture of shelters and clothing, appearance of art and other non-utilitarian products, development of cooperative hunting behaviour, and domestication of plant and animal species (leading to settled agricultural societies). All of these features allowed humans to have greater control of their environment, rather than responsive to it. Thus, the development of these skills would directly contribute to the survival of individuals (& groups) practising these behaviours. (Cultural evolution is also described as non-biological evolution, since what is transmitted to new generations is changes in learned behaviour patterns. However, any genetic underpinnings to these behaviours would also be passed on.)   Some aspects of cultural evolution are easier to trace than others. Examples of stone tools made by hominin species are relatively common and easily recognised. Tools made of other substances, such as wood or bone, do not survive so well in the stratigraphic record. Changes in behaviour, such as the development of cooperative hunting groups or changes in social structure, leave no direct traces at all and their presence must be inferred from other evidence.

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Evidence of developing human culture appears far back in time. Homo habilis was named for its association with the crude cobble tools of the Oldowan culture, and it’s possible that Australopithecus garhi  and one of the robust australopithecines, A. robustus , were also tool users. What differentiates these very simple, ancient tool-making cultures from the tool manufacture and use practised by modern chimpanzees? In fact, how do we define “culture” in the evolutionary sense?   At the time that H. habilis was discovered, manufacture and use of tools was generally viewed as an exclusively human activity. The Oldowan tools marked the earliest hard evidence of culture in our ancestors. We now know that many different animals use tools. Perhaps the best-known example is that of chimpanzees. Jane Goodall first documented this in her studies of wild chimpanzees in Africa’s Gombe Reserve. Not only did her animals use rocks, twigs and vegetation as simple tools, but they modified them: for example, stripping a twig of leaves, and breaking it to the right length, so that they could “fish” for termites in the insects’ tunnels. Young chimps learn these skills by observing their elders, an example of cultural transmission. And chimpanzees from different areas have distinctly different tool-making cultures.  However, one of the differences between chimp and human culture is that chimps seldom carry tools, or the raw materials for tool making, for any distance. In addition, chimps make tools only immediately before using them. Tools used by early humans were typically worked and reworked at different locations

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So is it the complexity of culture that sets humans apart? We think of complex culture as a hallmark of humanity. However, art works, such as jewellery, carving, and cave paintings, do not appear in the record until 30-40,000 years ago. This follows the development of the sophisticated Aurignacian tool kits associated with Cro-Magnon culture. Some authors suggest that the use of highly sophisticated language accompanied this flowering of culture, and marked the appearance of a significant capacity for abstract thought. (This is not to say that earlier humans, and hominins, were not capable of speech.)  Cultural evolution has occurred in different times in different places. This is a reflection both of the time at which different regions of the globe were settled, and also the nature of the biology & geology of an area, which poses constraints on, for example, the domestication of plants & animals. This has had far-reaching consequences on later geopolitical history.

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When did art begin?

The big debate is where and when the ‘human’ cultural and symbolic development began. Some point to the cultural explosion that occurred in Europe some 40,000 years ago, as demonstrated by the dazzling display of Aurignacian art such as that found in the French cave of Chauvet. This implies that Europeans were the first to speak, paint, carve, dress, weave and exchange goods. Others, however, provide evidence in Africa millenia before. It comes down to the evidence.

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In Africa, Makapansgat is the site of the discovery of the Makapansgat pebble. This is a 260-gram jasperite cobble with natural chipping and wear patterns that make it look like a crude rendition of a human face. The pebble, found some distance from any possible natural source, was in the possession of a female Australopithecus africanus, an early hominid living between 3 and 2 million years ago. The pebble was not a manufactured object, but it was possibly recognized it as a symbolic face, and treasured as such. This would make it the oldest known sculpture, or manuport [a natural object which has been moved from its original context by human agency but otherwise remains unmodified] known.  The Tan-Tan sculpture, discovered in ancient river deposits of the river Draa, Morocco, is between 500,000-300,000 years old. The overall shape of this little quartzite pebble, almost 6 cms in height, resembles a human figure but is entirely natural and unmodified by human action. Found near stone tools, it is possible that the pebble was simply collected and kept by someone who noticed its human shape. Examination under a microscope suggests this shape may have been emphasised by deliberate alteration of the natural grooves which run across the body.

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The Berekhat Ram sculpture, discovered in the Golan Heights, Israel, is between 250,000-280,000 years old. It may be the oldest known representation of a woman. This tiny piece – only 3.5 cms in height – of volcanic scoria, reddened by heat and incorporating specks of charcoal does not immediately resemble a figurine. Largely natural, it is the groove around the neck and others on the sides which have been shown to be deliberate modifications absent from other scoria found in the area. The grooves accentuate the natural shape to suggest a human form which has been drawn as female. Does it represent curiosity or artistry on the part of the hand-axe makers of Berekhat Ram?

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The Blombos ochre piece, from the Blombos cave in South Africa, is decorated with a delicate geometric pattern and has been dated conservatively at 77,000 years old. In fact, archaeologist Chris Henshilwood who found the ochre, believes it could be as much as 100,000 years old due to the more recent discovery of paint-workshop artefacts in the Blombos Cave. The cave paintings of Chauvet are up to 35,000 years old. European Palaeolithic art developed over a period of 25-20,000 years and continued until the end of the last ice age, 11,000 years ago. But the art of this time in Europe was not restricted to the paintings and engravings found on the walls of caves. Portable art, though often under-represented, was prevalent during this period. Sculptures depicting human figures, animal figures and therianthropes [hybrid figures, usually a human figure with an animal head] have been discovered. The Vogelherd Horse, discovered in Germany, is between 35,000 and 32,000 years old. The Lion Man of Hohlenstein-Stadel, discovered also in Germany, is 32,000 years old. Of a similar age is The ‘Dancing Figure’ of Galgenburg, discovered in Austria. The Lespugue figurine, discovered in France, is between 24,000 and 22,000 years old.

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It was art that gave Humans the edge over Neanderthals:

A new study suggests that prehistoric humans evolved to become the world’s dominant species, in part, because they created art. The hand-eye coordination and visualization skills developed by creating prehistoric cave drawings helped Homo sapiens master essential hunting skills, the study suggests, giving humans an advantage over their artless cousins, the Neanderthals. The paper was written by psychologist Richard Cross of the University of California-Davis, an expert on art and human evolution. It was published in the Evolutionary Studies in Imaginative Culture journal. In the paper, Cross maintains that there is “a causal relationship between the evolved ability of anatomically modern human to throw spears accurately while hunting and their ability to draw representational images.” The researcher argues that while Neanderthals used thrusting spears to hunt tamer prey in Eurasia, Homo sapiens were spear hunting much more dangerous and alert prey in Africa. As a result, he postulates that Homo sapiens developed a larger parietal cortex—the region of the brain that controls visual imagery and motor coordination. “Neanderthals could mentally visualize previously seen animals from working memory, but they were unable to translate those mental images effectively into the coordinated hand-movement patterns required for drawing,” Cross writes. On the other hand, Homo sapiens were actually sharpening their hunting skills by creating cave drawings, he says: “Since the act of drawing enhances observational skills, perhaps these drawings were useful for conceptualizing hunts, evaluating game attentiveness, selecting vulnerable body areas as targets, and fostering group cohesiveness via spiritual ceremonies.” To research his hypothesis, Cross studied 30,000-year-old drawings in the Chauvet-Pont-d’Arc Cave in southern France and concluded that the motions in the scrawls are similar to the arc that a thrown spear might take. In other words, prehistoric humans weren’t just doodling on cave walls; they were drafting plans, strategies, and representations that showed an acute awareness of their game. The nexus between hunting techniques and drawing prowess may not be intuitive, but if the study is correct, the link between the skills could be one reason why Homo sapiens thrived while the Neanderthals died off.

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How culture drove human evolution:

This approach, termed Dual Inheritance or Gene-Culture Coevolutionary Theory (Boyd & Richerson, 1985; Laland, et al., 1995), can be organized around three key concepts (Henrich & McElreath, 2007):

  1. Cultural capacities as adaptations: Culture, cultural transmission, and cultural evolution arise from genetically evolved psychological adaptations for acquiring ideas, beliefs, values, practices, mental models, and strategies from other individuals by observation and inference. Thus, the first step in theorizing is to use the logic of natural selection to develop hypotheses about the evolution and operation of our cultural learning capacities (Rendell et al., 2011).
  2. Cultural evolution: These cognitive adaptations give rise to a robust second system of inheritance (cultural evolution) that operates by different transmission rules than genetic inheritance, and can thus produce phenomena not observed in other less cultural species. Theorizing about these processes requires taking what we know about human cultural learning and cognition, embedding them into evolutionary models that include social interaction, and studying their emergent properties with the goal of making empirical predictions.
  3. Culture-gene coevolution: The second system of inheritance created by cultural evolution can alter both the social and physical environments faced by evolving genes, leading to a process termed gene-culture coevolution. For example, it appears that the practice of cooking spread by social learning in ancestral human populations. Once spread, ‘cooked food’ became a selective force that shrunk our digestive tracks, teeth, stomachs, and gape (Wrangham, 2009). Such a reduced investment in digestive tissues may have freed up energy for more brain building, and perhaps a greater reliance on cultural information. Cultural traits alter the social and physical environments under which genetic selection operates. For example, the cultural adoptions of agriculture and dairying have, in humans, caused genetic selection for the traits to digest starch and lactose, respectively. Empirical evidence from genetics suggests that culture has long shaped our genome (Laland, et al., 2010; Richerson, et al., 2010).

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Clinical consequences of human evolution shaped by cultural trends a 2013 study:

Recent reports suggest that increased human population size, decreased negative selection pertaining to some phenotypes and associated genotypes and a possibly increased de novo mutation burden for newborns that relates to paternal age at conception are contributing to an expansion of human genetic diversity. Some of this diversity can be expected to contribute to disease. Because all of the preceding diversity-enhancing factors are to a significant degree consequences of cultural developments, it can be argued that the future clinical burden of the human population will be shaped in part by a human evolutionary trajectory substantially influenced by culturally mediated effects on the number of mutations in the gene pool and on the intensity of selection on some of the phenotypes associated with new genetic variants.

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Several recent studies have added, or at least highlighted, a twist to the rather familiar conception of human evolution and this new variation on the standard theme may have substantial implications for both biomedical research and clinical medicine. Two of these studies, published recently determined the nucleotide sequences of thousands or hundreds of human protein-coding genes in thousands of people. What their data revealed was that there were many rare (frequency <0.5%) genetic variants, most of which were previously unknown and relatively localized geographically or ethnically. These mutations were enriched among individuals with diagnosable medical conditions. Although there may always be some holdouts, especially among non-experts and non-scientists, most biomedical scientists and biologists recognize that humans have not stopped evolving and continue to be subject to selection and to change at a population level, however slowly or subtly. In terms of both genotypes and phenotypes, there is growing evidence for human evolution in response to selection.

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The authors of both of the recent studies on the prevalence of rare genetic variants cited above inferred that many of the rare variants they described were surviving in the human population in part because selection against certain types of functional deficits was diminished in recent decades in comparison with the past. Examples of medical advances that have saved many lives and likely permitted the generation of offspring who would not otherwise have been born include blood and marrow transplantation for pediatric lymphoid malignancies and vaccines against pediatric pathogens capable of causing mortality. Since 1971, over a million individuals have received hematopoietic cell transplants, generally for otherwise fatal diseases. A significant proportion of these recipients were of reproductive age or younger. The implementation of routine immunization for diphtheria, mumps, pertussis and tetanus resulted in a greater than 99% reduction in mortality from these infectious diseases between 1940 and 2004. If instead we consider a disease directly associated with mutations at a single locus, such as cystic fibrosis (CF), the improvement in mortality over the past 40 years is also highly significant. For example, in the UK, in the period from 1968 to 1970, approximately half of the population of males or females succumbed to the disease by the time of entry into reproductive competency, but by the early 1990s, the majority of UK CF patients could be expected to survive well into their reproductive years. Similar data have been obtained in Australian CF patients. There are undoubtedly a number of other potentially fatal conditions associated with one or more alleles at a single predominant genetic locus where improvements in care have increased survival and reproductive success.

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In part as a consequence of the contributions of public health measures and advances in medical care, an increased pace of population growth has been sustained for many generations and has made available many new genetic variants for which selection has had insufficient time to act irrespective of any attenuation of selection intensity. The enormously expanded human population of recent decades has also meant that there are many more opportunities for genomes to sample what might be regarded as the envelope of human genetic possibility. It is sobering to realize that, starting with any particular human genome, the number of possible genomes one mutational step away is three raised to roughly the three billionth power, a number staggeringly larger than estimates for the number of atoms in the universe (which generally cluster around 10^79 to 10^80), a reasonable gold standard for impressive magnitudes.

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Another even more recent study found that the number of new mutations in offspring is strongly correlated with the age of the father at the time of conception. This correlation helps to explain the substantial correlation between the occurrence of de novo mutation and the incidence of autism. According to Kong et al., the average newborn has 60 new small-scale mutations, but the paternal contribution can vary over a wide range from about 25 for a 20-year-old father to 65 for a 40-year-old father with a fairly constant 15 new mutations contributed by the mother. Available evidence suggests that up to 10% of new point mutations are expected to be deleterious, so it is expected that, on average, each newborn could have as many as six new potentially disease-causing genetic alterations.

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One far-reaching implication of these new results is that personalized medicine pertaining to some conditions will likely face greater obstacles than previously believed. Establishing the causal connections between rare variants found in geographically circumscribed populations and diseases or other medically relevant phenotypes will be much more difficult, requiring much larger study sample sizes for example, than has been the case for more common variants that occur in multiple populations on different continents. Furthermore, once such causal links are established, developing relevant genetically guided diagnostic tests or therapies could be more challenging than has generally been assumed.

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Thus, the crux of the current thesis is (i) due to cultural developments such as technologically advanced medical care, public health measures and increased food availability, there are many more human genomes subject to mutation than there otherwise would be and (ii) many new variants that in a context with less medical technology, public health infrastructure and food availability would be much more likely to disappear quickly now persist in the human population. So cultural developments have made it possible for more human genetic variants to arise and, by relaxing selection on many of the variant-associated phenotypes, allowed far more of these variants to persist in the human genome pool. A culturally mediated increase in mutation rate may further enhance this process but is not essential for its general direction.

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Of course, strong interactions between cultural evolution and biological evolution have been noted before, and the empirical evidence supporting such interactions is consistent with theoretical analyses. A now widely cited and well-accepted example of cultural influence on human evolution is the effect of dairying on the frequency of alleles that favor the adult persistence of lactase expression in the intestines. In this study, Tishkoff et al. reported evidence implicating several independently originating variants associated with lactase persistence in European and African populations due to positive selection.

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The new data, in contrast, reveal the persistence and possible spread of variants primarily due to a lack of selection resulting from cultural factors. These results further support the argument that cultural and biological forms of evolution are better regarded as a single integrated process than as separate influences on human populations. Physicians who understand these realities will be better able to understand the eternally changing spectrum of human disease and disability.

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Environmental stress, human adaptations and culture:

Culture is often defined as human achievements—artistic expression, science, technology, morals and laws, for example—but it can be defined more simply as shared, learned social behaviour, or a non-biological means of adaptation that extends beyond the body (White, 1959). In this respect, humans have been regarded as a species so dependent on culture and technology that cultural adaptation has replaced biological adaptation. During the past 12,000 years, humans have increasingly used culture and technology—built upon agriculture and animal domestication—to control and modify the natural environment. Therefore, culture has an important role in understanding whether evolution is still influencing the biology of our species.

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Adaptation, in the simplest sense, is a mechanism that allows organisms to mediate the stresses of their environment to ensure survival and reproduction. We often think that adaptation takes place through direct genetic modifications in response to environmental stress. However, many animal species are able to accommodate environmental stress simply by changing their behaviour in response to environmental conditions, without the need to resort to genetic adaptation. This could involve modifications as simple as moving to another area, changing annual or daily activities, or changing strategies for food procurement. If behavioural flexibility cannot accommodate environmental stress, animals also have a range of physiological mechanisms that help them to respond—again, without the need for genetic adaptation. Examples include adaptive changes in heart rate, respiration and the accumulation of body fat. In combination, behavioural and physiological flexibility form a two-tiered defence against environmental stress as seen in the figure below. These mechanisms might be linked to the regulation of genes, but their variability might be mediated by environmental conditions without changes in gene frequency. If these defences fail or only partly buffer against environmental stress, then survivorship or reproductive rates might vary. In this case, changes in gene frequencies will occur over time and evolution will take place.

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Figure above shows model of the relationship between the environment and human adaptation.

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How do humans fit into this two-tiered system of defence against environmental stress? Most importantly, we have developed an extensive dependence on culture and technology that has allowed us to populate the most extreme environments worldwide. There is also evidence that other complex social species such as chimpanzees show cultural variability that is important for their survival (McGrew, 2004). However, our dependence on technology can be seen as different to that of other species in our capacity for cumulative cultural change, which provides greater potential to remove humans from a direct relationship with the natural world.

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The earliest direct evidence of this trend might have been the first use of fire roughly 700,000 years ago, which probably allowed the early human species Homo heidelbergensis to spread into and occupy northern latitudes. We know from the fossil record that anatomically modern humans, Homo sapiens, originated in Africa between 150,000 and 200,000 years ago, but did not migrate to other parts of the world until between 50,000 and 70,000 years ago. Evidence of what we can call ‘modern human behaviour’ appears in the archaeological record over a long period of time, from 300,000 to 50,000 years ago. It was not until early humans had developed a complete range of behaviour that we consider to be ‘modern’—including artistic expression and symbolism—that they colonized all habitable regions of the world. Culture and technology were clearly crucial to the successful colonization of the world by our species. They allowed us to occupy most regions of the planet through the use of fire, housing, watercraft, versatile tools and cognition, which enormously improved our ability to hunt and forage for food in markedly different environments—and, in the process, to occupy more environmental niches than most other species.

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Nepotism has its Benefits when it comes to Survival:

Evolution influences every aspect of the form and behaviour of organisms. Most prominent are the specific behavioural and physical adaptations that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by cooperating with each other, usually by aiding their relatives or engaging in mutually beneficial symbiosis. Kin selection theory predicts that individuals gain inclusive fitness benefits from cooperating with relatives, because the costs of helping is outweighed by the increased fitness of individuals with whom they share genes identical by decent. Coined as Hamilton’s rule, it follows that inclusive fitness gained through helping behaviour will generally increase with the relatedness coefficient between helper and receiver. This should select for kin discrimination, as directing help towards relatives requires the ability to distinguish kin from non-kin, based on either environmentally or genetically determined cues. Indeed, there is wide evidence for kin discrimination in social animals, emphasizing the significance of nepotism, i.e. preferential cooperation with kin, in social evolution. Given that recognition systems are costly to maintain, kin discrimination is expected to be most pronounced when there are significant inclusive fitness benefits of nepotism.

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An evolutionary model explains Neolithic transition from egalitarianism to leadership and despotism a 2014 study:

The Neolithic was marked by a transition from small and relatively egalitarian groups to much larger groups with increased stratification. But, the dynamics of this remain poorly understood. It is hard to see how despotism can arise without coercion, yet coercion could not easily have occurred in an egalitarian setting. Using a quantitative model of evolution in a patch-structured population, authors demonstrate that the interaction between demographic and ecological factors can overcome this conundrum. Authors model the coevolution of individual preferences for hierarchy alongside the degree of despotism of leaders, and the dispersal preferences of followers. They show that voluntary leadership without coercion can evolve in small groups, when leaders help to solve coordination problems related to resource production. An example is coordinating construction of an irrigation system. Their model predicts that the transition to larger despotic groups will then occur when: (i) surplus resources lead to demographic expansion of groups, removing the viability of an acephalous (headless, without leader) niche in the same area and so locking individuals into hierarchy; (ii) high dispersal costs limit followers’ ability to escape a despot. Empirical evidence suggests that these conditions were probably met, for the first time, during the subsistence intensification of the Neolithic.

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Evolution and lifestyle diseases:

In the course of a few generations, conditions that were once rare, such as obesity, diabetes, hypertension, and heart attacks are now contributing to a global epidemic of metabolic disease. As one of its core questions, the field of evolutionary medicine seeks to understand the origins of these health trends. A central assumption is that the human genome gradually became adapted to the diet, behavior, and reproductive and social practices of our ancestors, who subsisted for several million years as band-level foragers. We also know that our human genome changes fairly slowly, and several researchers have therefore focused on the connection between our human genes and the current diet and lifestyle.  The slow pace of genetic change means that these genetic adaptations linger as a sort of biological memory of ancestral experience, and the health impacts of our current lifestyle can best be understood as an interaction between that memory and the dramatically changed diet and lifestyle that many of us experience today.

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The DNA we receive from our mother and father code for thousands of different enzymes, hormones, and other proteins. Although we inherit our DNA from mom and dad, the way we express the genes in our genome is largely determined by our diet and lifestyle. The current dietary pattern (fast food and junk food), characterized by high intakes of sugar, flours, salt and refined fats, seems to increase expression of genes involved in chronic disease.  Modern diseases could also be due to the mismatch between our current lifestyles and those of our ancestors. Modernisation has drastically changed our diets, daily routine, social structures and reproductive lives. Metabolic syndrome fits this picture. It is linked to unhealthy and large diets that overload the body’s metabolism and the decrease in activity seen in modern lifestyles. We eat far more food and burn far fewer calories than that at any other point in our evolutionary history, and the effects of our sedentary lifestyles are seen in the increasing incidence of diabetes, hypertension, heart disease and obesity.

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The Evolutionary Mismatch Hypothesis a 2017 study:

Evolutionary mismatch occurs when the environment that organisms are adapted to, via a slow process of biological evolution, changes so quickly and intensely that it hinders these organisms to fulfil their reproductive needs. Take an example from nature. Deforestation has changed the habitats of many species so profoundly that they are no longer able to thrive, or even survive, in these altered environments. Just consider the alarming reports of the decline in Borneo’s orangutans’ populations, the result of human interference that is destroying their habitats. Mismatches such as these are forced upon a species (think of the meteorite strike that called off the dinosaurs). Other mismatches occur because environmental changes hijack psychological systems such that individuals of a species make the wrong kinds of choices.

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Mismatch hypothesis help us to understand all kinds of ills of modern society, from depression to drug-abuse, from bottle-feeding to bad parenting, and from toxic leadership to stress in the workplace. The basic tenet of mismatch hypothesis is that if we have two options, A and B, mismatch occurs when we prefer option B, where option A would be better for us in the long run. Take the classic example of food-intake. Humans have an evolved preference for high-calorie foods—this preference helped them survive in ancestral environments where food supplies were short. Yet, in the modern world, high-calorie foods are abundant and easy to get, and so humans would be better off showing some restraint in what they eat and how much. Yet many of us lack in self-control, which was not needed in our ancestral environment, and the result is an epidemic of obesity, diabetes, and heart disease. Mental health problems may also result from mismatch. For instance, postpartum depression may be the result of living in an environment where the physical (diet, sunlight exposure) and social resources (a tight family network) are lacking to cope with the increasing demands of child care. Postpartum depression rates in the U.S. are lower, for instance, among young mothers from relatively poor but supportive families than those from more privileged backgrounds (this phenomenon is also known as the Latina paradox).

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Problems in the modern workplace may also result from the mismatch. More than 99 percent of human evolution took place in small-scale societies, hunter-gatherer groups of 50-150 individuals that roamed the savannah looking for food and safety. These were societies without bosses, production targets, and pension plans. There was no strict separation between work and private life. Only since the agricultural revolution, the last 1 percent of human evolution, did human societies grow in scale and complexity and this produced toxic work arrangements for many. The agricultural revolution, and thereafter the industrial revolution, produced inequalities in health, income, and decision-making power, and a marked separation between one’s private and work life—conditions unknown to our ancestors. In small-scale societies, trust and cooperation are established on the basis of frequent face-to-face interactions. Yet these interactions are increasingly lacking as remote workplace arrangements have become the norm. Small-scale societies have no formal leaders and status and power differences between individuals were minimal. Yet modern organizations have CEOs with excessive pay schemes and middle managers who in principle can control all aspects of your working life. The result is job stress, job alienation, and the potential for corruption and power abuse. Work also causes many novel stressors like handling deadlines and dealing with temporary contracts that were unknown to our ancestors, these are stressors that our immune system is poorly adapted to.

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Misconceptions regarding evolution:

  1. Misconception: Evolution and religion are incompatible.

Correction: Because of some individuals and groups stridently declaring their beliefs, it’s easy to get the impression that science (which includes evolution) and religion are at war; however, the idea that one always has to choose between science and religion is incorrect. People of many different faiths and levels of scientific expertise see no contradiction at all between science and religion. For many of these people, science and religion simply deal with different realms. Science deals with natural causes for natural phenomena, while religion deals with beliefs that are beyond the natural world. Of course, some religious beliefs explicitly contradict science (e.g., the belief that the world and all life on it was created in six literal days does conflict with evolutionary theory); however, most religious groups have no conflict with the theory of evolution or other scientific findings. Some people erroneously believe that evolution and religious faith are incompatible and so assume that accepting evolutionary theory encourages immoral behavior. Neither is correct.  In fact, many religious people, including theologians, feel that a deeper understanding of nature actually enriches their faith. Moreover, in the scientific community there are many scientists who are devoutly religious and also accept evolution. In my view, evolution proves that God did not create life and as a corollary, God does not exist. But that is my view and you are entitled your view.

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  1. Misconception: Natural selection involves organisms trying to adapt.

Correction: Natural selection leads to the adaptation of species over time, but the process does not involve effort, trying, or wanting. Natural selection naturally results from genetic variation in a population and the fact that some of those variants may be able to leave more offspring in the next generation than other variants. That genetic variation is generated by random mutation — a process that is unaffected by what organisms in the population want or what they are “trying” to do. Either an individual has genes that are good enough to survive and reproduce, or it does not; it can’t get the right genes by “trying.” For example bacteria do not evolve resistance to our antibiotics because they “try” so hard. Instead, resistance evolves because random mutation happens to generate some individuals that are better able to survive the antibiotic, and these individuals can reproduce more than other, leaving behind more resistant bacteria. On the other hand, there are bacteria who are always sensitive to penicillin for decades because they could not generate random mutation to combat penicillin.

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  1. Misconception: Natural selection gives organisms what they need.

Correction: Natural selection has no intentions or senses; it cannot sense what a species or an individual “needs.” Natural selection acts on the genetic variation in a population, and this genetic variation is generated by random mutation — a process that is unaffected by what organisms in the population need. If a population happens to have genetic variation that allows some individuals to survive a challenge better than others or reproduce more than others, then those individuals will have more offspring in the next generation, and the population will evolve. If that genetic variation is not in the population, the population may survive anyway (but not evolve via natural selection) or it may die out. But it will not be granted what it “needs” by natural selection.

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  1. Misconception: Natural selection acts for the good of the species.

Correction: When we hear about altruism in nature (e.g., dolphins spending energy to support a sick individual, or a meerkat calling to warn others of an approaching predator, even though this puts the alarm sounder at extra risk), it’s tempting to think that those behaviors arose through natural selection that favors the survival of the species — that natural selection promotes behaviors that are good for the species as a whole, even if they are risky or detrimental for individuals in the population. However, this impression is incorrect. Natural selection has no foresight or intentions. In general, natural selection simply selects among individuals in a population, favoring traits that enable individuals to survive and reproduce, yielding more copies of those individuals’ genes in the next generation. Theoretically, in fact, a trait that is advantageous to the individual (e.g., being an efficient predator) could become more and more frequent and wind up driving the whole population to extinction (e.g., if the efficient predation actually wiped out the entire prey population, leaving the predators without a food source).

So what’s the evolutionary explanation for altruism if it’s not for the good of the species?

There are many ways that such behaviors can evolve. For example, if altruistic acts are “repaid” at other times, this sort of behavior may be favored by natural selection. Similarly, if altruistic behavior increases the survival and reproduction of an individual’s kin (who are also likely to carry altruistic genes), this behavior can spread through a population via natural selection.

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  1. Misconception: Natural selection is about survival of the very fittest individuals in a population.

Correction: Though “survival of the fittest” is the catchphrase of natural selection, “survival of the fit enough” is more accurate. In most populations, organisms with many different genetic variations survive, reproduce, and leave offspring carrying their genes in the next generation. It is not simply the one or two “best” individuals in the population that pass their genes on to the next generation. This is apparent in the populations around us: for example, a plant may not have the genes to flourish in a drought, or a predator may not be quite fast enough to catch her prey every time she is hungry. These individuals may not be the “fittest” in the population, but they are “fit enough” to reproduce and pass their genes on to the next generation.

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  1. Misconception: Natural selection produces organisms perfectly suited to their environments.

Correction: Natural selection is not all-powerful. There are many reasons that natural selection cannot produce “perfectly-engineered” traits. For example, living things are made up of traits resulting from a complicated set of trade-offs — changing one feature for the better may mean changing another for the worse (e.g., a bird with the “perfect” tail plumage to attract mates maybe be particularly vulnerable to predators because of its long tail). And of course, because organisms have arisen through complex evolutionary histories (not a design process), their future evolution is often constrained by traits they have already evolved. For example, even if it were advantageous for an insect to grow in some way other than molting, this switch simply could not happen because molting is embedded in the genetic makeup of insects at many levels.

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  1. Misconception: All traits of organisms are adaptations.

Correction: Because living things have so many impressive adaptations (incredible camouflage, sneaky means of catching prey, flowers that attract just the right pollinators, etc.), it’s easy to assume that all features of organisms must be adaptive in some way — to notice something about an organism and automatically wonder, “Now, what’s that for?” While some traits are adaptive, it’s important to keep in mind that many traits are not adaptations at all. Some may be the chance results of history. For example, the base sequence GGC codes for the amino acid glycine simply because that’s the way it happened to start out — and that’s the way we inherited it from our common ancestor. There is nothing special about the relationship between GGC and glycine. It’s just a historical accident that stuck around. Others traits may be by-products of another characteristic. For example, the color of blood is not adaptive. There’s no reason that having red blood is any better than having green blood or blue blood. Blood’s redness is a by-product of its chemistry, which causes it to reflect red light. The chemistry of blood may be an adaptation, but blood’s color is not an adaptation.

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  1. Misconception: Evolution can’t explain complex organs.

Correction: A common argument in favour of creationism is the evolution of the eye. A half developed eye would serve no function, so how can natural selection slowly create a functional eye in a step-wise manner? Darwin himself suggested that the eye could have had its origins in organs with different functions. Organs that allow detection of light could then have been favoured by natural selection, even if it did not provide full vision. These ideas have been proven correct many years later by researchers studying primitive light-sensing organs in animals. In molluscs like snails and segmented worms, light-sense cells spread across the body surface can tell the difference between light and dark.

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  1. Misconception: Evolution results in progress; organisms are always getting better through evolution.

Correction: One important mechanism of evolution, natural selection, does result in the evolution of improved abilities to survive and reproduce; however, this does not mean that evolution is progressive — for several reasons. First, natural selection does not produce organisms perfectly suited to their environments. It often allows the survival of individuals with a range of traits — individuals that are “good enough” to survive. Hence, evolutionary change is not always necessary for species to persist. Many taxa (like some mosses, fungi, sharks, opossums, and crayfish) have changed little physically over great expanses of time. Second, there are other mechanisms of evolution that don’t cause adaptive change. Mutation, migration, and genetic drift may cause populations to evolve in ways that are actually harmful overall or make them less suitable for their environments. For example, the Afrikaner population of South Africa has an unusually high frequency of the gene responsible for Huntington’s disease because the gene version drifted to high frequency as the population grew from a small starting population. Finally, the whole idea of “progress” doesn’t make sense when it comes to evolution. Climates change, rivers shift course, new competitors invade — and an organism with traits that are beneficial in one situation may be poorly equipped for survival when the environment changes. And even if we focus on a single environment and habitat, the idea of how to measure “progress” is skewed by the perspective of the observer. From a plant’s perspective, the best measure of progress might be photosynthetic ability; from a spider’s it might be the efficiency of a venom delivery system; from a human’s, cognitive ability. It is tempting to see evolution as a grand progressive ladder with Homo sapiens emerging at the top. But evolution produces a tree, not a ladder — and we are just one of many twigs on the tree.

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  1. Misconception: Individual organisms can evolve during a single lifespan.

Correction: Evolutionary change is based on changes in the genetic makeup of populations over time. Populations, not individual organisms, evolve. Changes in an individual over the course of its lifetime may be developmental (e.g., a male bird growing more colorful plumage as it reaches sexual maturity) or may be caused by how the environment affects an organism (e.g., a bird losing feathers because it is infected with many parasites); however, these shifts are not caused by changes in its genes. While it would be handy if there were a way for environmental changes to cause adaptive changes in our genes — who wouldn’t want a gene for malaria resistance to come along with a vacation to Mozambique? — evolution just doesn’t work that way. New gene variants (i.e., alleles) are produced by random mutation, and over the course of many generations, natural selection may favor advantageous variants, causing them to become more common in the population.

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  1. Misconception: Evolution only occurs slowly and gradually.

Correction: Evolution occurs slowly and gradually, but it can also occur rapidly. We have many examples of slow and steady evolution — for example, the gradual evolution of whales from their land-dwelling, mammalian ancestors, as documented in the fossil record. But we also know of many cases in which evolution has occurred rapidly. For example, we have a detailed fossil record showing how some species of single-celled organism, called foraminiferans, evolved new body shapes in the blink of a geological eye. Similarly, we can observe rapid evolution going on around us all the time. Over the past 50 years, we’ve observed squirrels evolve new breeding times in response to climate change, a fish species evolve resistance to toxins dumped into the Hudson River, and a host of microbes evolve resistance to new drugs we’ve developed. Many different factors can foster rapid evolution — small population size, short generation time, big shifts in environmental conditions — and the evidence makes it clear that this has happened many times.

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  1. Misconception: Genetic drift only occurs in small populations.

Correction: Genetic drift has a larger effect on small populations, but the process occurs in all populations — large or small. Genetic drift occurs because, due to chance, the individuals that reproduce may not exactly represent the genetic makeup of the whole population. For example, in one generation of a population of captive mice, brown-furred individuals may reproduce more than white-furred individuals, causing the gene version that codes for brown fur to increase in the population — not because it improves survival, just because of chance. The same process occurs in large populations: some individuals may get lucky and leave many copies of their genes in the next generation, while others may be unlucky and leave few copies. This causes the frequencies of different gene versions to “drift” from generation to generation. However, in large populations, the changes in gene frequency from generation to generation tend to be small, while in smaller populations, those shifts may be much larger. Whether its impact is large or small, genetic drift occurs all the time, in all populations. It’s also important to keep in mind that genetic drift may act at the same time as other mechanisms of evolution, like natural selection and migration.

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  1. Misconception: Species are distinct natural entities, with a clear definition, that can be easily recognized by anyone.

Correction: Many of us are familiar with the biological species concept, which defines a species as a group of individuals that actually or potentially interbreed in nature. That definition of a species might seem cut and dried — and for many organisms (e.g., mammals), it works well — but in many other cases, this definition is difficult to apply. For example, many bacteria reproduce mainly asexually. How can the biological species concept be applied to them? Many plants and some animals form hybrids in nature, even if they largely mate within their own groups. Should groups that occasionally hybridize in selected areas be considered the same species or separate species? The concept of a species is a fuzzy one because humans invented the concept to help get a grasp on the diversity of the natural world. It is difficult to apply because the term species reflects our attempts to give discrete names to different parts of the tree of life — which is not discrete at all, but a continuous web of life, connected from its roots to its leaves.

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  1. Misconception: Humans can’t negatively impact ecosystems, because species will just evolve what they need to survive.

Correction: As discussed earlier, natural selection does not automatically provide organisms with the traits they “need” to survive. Of course, some species may possess traits that allow them to thrive under conditions of environmental change caused by humans and so may be selected for, but others may not and so may go extinct. If a population or species doesn’t happen to have the right kinds of genetic variation, it will not evolve in response to the environmental changes wrought by humans, whether those changes are caused by pollutants, climate change, habitat encroachment, or other factors. For example, as climate change causes the Arctic sea ice to thin and break up earlier and earlier, polar bears are finding it more difficult to obtain food. If polar bear populations don’t have the genetic variation that would allow some individuals to take advantage of hunting opportunities that are not dependent on sea ice, they could go extinct in the wild.

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  1. Misconception: The fittest organisms in a population are those that are strongest, healthiest, fastest, and/or largest.

Correction: Without differences in fitness natural selection cannot act and adaptation cannot occur.  In evolutionary terms, fitness has a very different meaning than the everyday meaning of the word. An organism’s evolutionary fitness does not indicate its health, but rather its ability to get its genes into the next generation. Although biologists have offered a staggering number of definitions of fitness, they agree broadly on the essence of the idea. In the crudest terms, fitness involves the ability of organisms— or, more rarely, populations or species— to survive and reproduce in the environment in which they find themselves. The consequence of this survival and reproduction is that organisms contribute genes to the next generation. The more fertile offspring an organism leaves in the next generation, the fitter it is. This doesn’t always correlate with strength, speed, or size. For example, a puny male bird with bright tail feathers might leave behind more offspring than a stronger, duller male, and a spindly plant with big seed pods may leave behind more offspring than a larger specimen — meaning that the puny bird and the spindly plant have higher evolutionary fitness than their stronger, larger counterparts.

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  1. Misconception: Evolution is not science because it is not observable or testable.

Correction: This misconception encompasses two incorrect ideas: (1) that all science depends on controlled laboratory experiments, and (2) that evolution cannot be studied with such experiments. First, many scientific investigations do not involve experiments or direct observation. Astronomers cannot hold stars in their hands and geologists cannot go back in time, but both scientists can learn a great deal about the universe through observation and comparison. In the same way, evolutionary biologists can test their ideas about the history of life on Earth by making observations in the real world. Second, though we can’t run an experiment that will tell us how the dinosaur lineage radiated, we can study many aspects of evolution with controlled experiments in a laboratory setting. In organisms with short generation times (e.g., bacteria or fruit flies), we can actually observe evolution in action over the course of an experiment. And in some cases, biologists have observed evolution occurring in the wild.

Because for many species, humans included, evolution happens over the course of many thousands of years, it is rare to observe the process in a human lifetime. Usually only laboratory scientists studying quickly reproducing life forms, like single-celled creatures and some invertebrates, have the opportunity to see evolutionary change happen before their eyes. All of us can and do experience the indirect effects of evolution nearly every day, however. One of the more important evolutionary concerns facing humans today is the emergence of antibiotic-resistant microbes. A battle against bacteria that we have been winning with medicine for the last 50 years or so is now an even race, according to some scientists — because of the rapid rate of bacterial evolution. Similarly, the use of pesticides in agriculture has driven the evolution of resistant insects that require more or harsher chemicals to be killed. Scientists studying Galapagos finches have seen evolutionary changes in beak size and shape in just a few years. Major evolutionary transformations take much, much longer time and therefore not observable.

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  1. Misconception: Evolution is ‘just’ a theory.

Correction: This misconception stems from a mix-up between casual and scientific use of the word theory. In everyday language, theory is often used to mean a hunch with little evidential support. Scientific theories, on the other hand, are broad explanations for a wide range of phenomena. In order to be accepted by the scientific community, a theory must be strongly supported by many different lines of evidence. Evolution is a well-supported and broadly accepted scientific theory; it is not ‘just’ a hunch.

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  1. Misconception: Evolutionary theory is invalid because it is incomplete and cannot give a total explanation for the biodiversity we see around us.

Correction: This misconception stems from a misunderstanding of the nature of scientific theories. All scientific theories (from evolutionary theory to atomic theory) are works in progress. As new evidence is discovered and new ideas are developed, our understanding of how the world works changes and so too do scientific theories. While we don’t know everything there is to know about evolution (or any other scientific discipline, for that matter), we do know a great deal about the history of life, the pattern of lineage-splitting through time, and the mechanisms that have caused these changes. And more will be learned in the future. Evolutionary theory, like any scientific theory, does not yet explain everything we observe in the natural world. However, evolutionary theory does help us understand a wide range of observations (from the rise of antibiotic-resistant bacteria to the physical match between pollinators and their preferred flowers), does make accurate predictions in new situations (e.g., that treating AIDS patients with a cocktail of medications should slow the evolution of the virus), and has proven itself time and time again in thousands of experiments and observational studies. To date, evolution is the only well-supported explanation for life’s diversity.

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  1. Misconception: Gaps in the fossil record disprove evolution.

Correction: While it’s true that there are gaps in the fossil record, this does not constitute evidence against evolutionary theory. Scientists evaluate hypotheses and theories by figuring out what we would expect to observe if a particular idea were true and then seeing if those expectations are borne out. If evolutionary theory were true, then we’d expect there to have been transitional forms connecting ancient species with their ancestors and descendants. This expectation has been borne out. Paleontologists have found many fossils with transitional features, and new fossils are discovered all the time. However, if evolutionary theory were true, we would not expect all of these forms to be preserved in the fossil record. Many organisms don’t have any body parts that fossilize well, the environmental conditions for forming good fossils are rare, and of course, we’ve only discovered a small percentage of the fossils that might be preserved somewhere on Earth. So scientists expect that for many evolutionary transitions, there will be gaps in the fossil record.

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  1. Misconception: The theory of evolution is flawed, but scientists won’t admit it.

Correction: Scientists have studied the supposed “flaws” that anti-evolution groups claim exist in evolutionary theory and have found no support for these claims. These “flaws” are based on misunderstandings of evolutionary theory or misrepresentations of the evidence. As scientists gather new evidence and as new perspectives emerge, evolutionary theory continues to be refined, but that doesn’t mean that the theory is flawed. Science is a competitive endeavour, and scientists would be eager to study and correct “flaws” in evolutionary theory if they existed.

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  1. Misconception: Evolution is a theory in crisis and is collapsing as scientists lose confidence in it.

Correction: Evolutionary theory is not in crisis; scientists accept evolution as the best explanation for life’s diversity because of the multiple lines of evidence supporting it, its broad power to explain biological phenomena, and its ability to make accurate predictions in a wide variety of situations. Scientists do not debate whether evolution took place, but they do debate many details of how evolution occurred and occurs in different circumstances. Antievolutionists may hear the debates about how evolution occurs and misinterpret them as debates about whether evolution occurs. Evolution is sound science and is treated accordingly by scientists and scholars worldwide.

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  1. Misconception: Most biologists have rejected ‘Darwinism’.

Correction: It is true that we have learned a lot about evolution since Darwin’s time. Today, we understand the genetic basis for the inheritance of traits, we can date many events in the fossil record to within a few hundred thousand years, and we can study how evolution has shaped development at a molecular level. These advances — ones that Darwin likely could not have imagined — have expanded evolutionary theory and made it much more powerful; however, they have not overturned the basic principles of evolution by natural selection and common ancestry that Darwin laid out, but have simply added to them. It’s important to keep in mind that elaboration, modification, and expansion of scientific theories is a normal part of the process of science.

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  1. Misconception: Evolution supports the idea of ‘might make right’ and rationalizes the oppression of some people by others.

Correction: In the nineteenth and early twentieth centuries, a philosophy called Social Darwinism arose from a misguided effort to apply lessons from biological evolution to society. Social Darwinism suggests that society should allow the weak and less fit to fail and die and that this is good policy and morally right. Supposedly, evolution by natural selection provided support for these ideas. Pre-existing prejudices were rationalized by the notion that colonized nations, poor people, or disadvantaged minorities must have deserved their situations because they were “less fit” than those who were better off. In this case, science was misapplied to promote a social and political agenda. While Social Darwinism as a political and social orientation has been broadly rejected, the scientific idea of biological evolution has stood the test of time.

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  1. Misconception: If students are taught that they are animals, they will behave like animals.

Correction: Part of evolutionary theory includes the idea that all organisms on Earth are related. The human lineage is a small twig on the branch of the tree of life that constitutes all animals. This means that, in a biological sense, humans are animals. We share anatomical, biochemical, and behavioral traits with other animals. For example, we humans care for our young, form cooperative groups, and communicate with one another, as do many other animals. And of course, each animal lineage also has behavioral traits that are unique to that lineage. In this sense, humans act like humans, slugs act like slugs, and squirrels act like squirrels. Some people misinterpret the fact that evolution has shaped animal behavior as supporting the idea that whatever behaviors are “natural” are the “right” ones. This is not the case.  It is unlikely that children, upon learning that they are related to all other animals, will start behaving like cows or goats.

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Why Evolution is Important:

Understanding evolution helps us solve biological problems that impact our lives. There are excellent examples of this in the field of medicine. To stay one step ahead of pathogenic diseases, researchers must understand the evolutionary patterns of disease-causing organisms. To control hereditary diseases in people, researchers study the evolutionary histories of the disease-causing genes. In these ways, knowledge of evolution can improve the quality of human life.

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The outbreak of the H1N1 “swine flu” in 2009 reminds us of our vulnerability to emerging diseases. Like SARS in 2002, H1N1’s abrupt appearance emphasizes the fact that viruses evolve, producing new and potentially pandemic-causing contagions. In our highly mobile world, new viruses can jump continents in mere hours via planes. Rapid evolution combined with rapid travel mean that emerging diseases threaten human health as never before—and therefore, understanding how these diseases evolve is vital as never before.  One reason no vaccine against HIV has yet been found is that HIV is one of the fastest evolving entities known to science. HIV’s rapid adaptability means that the key to defeating this scourge may lie in better understanding of how viruses evolve. Evolution helps us understand HIV’s origins. Because we know that HIV and SIV (simian immunodeficiency virus) share a common viral ancestor, this opens other avenues of research into ultimately defeating HIV. The technique of applying drug cocktails to HIV-infected patients has proven remarkably successful. The evolutionary idea with drug cocktails is that because HIV evolves so quickly, one single drug will usually leave some surviving viruses; a multi-drug approach has better success. Moreover, periodically switching the cocktail’s components helps eliminate viruses which have evolved resistance. All of these techniques rest upon a scientific understanding of evolution.

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With the exception of clean drinking water, few technologies have improved human health more than vaccines. Vaccines work so well, in fact, that today the horrors of smallpox and polio epidemics are fading memories. Vaccines exploit the efficiency of our own immune system to recognize and eliminate microbial threats that have been previously introduced into our bodies. Because these threats evolve, vaccines must change too. The flu shot you received this year will not protect you against next year’s bug because flu viruses evolve quickly. Evolution makes sense of the need for a new vaccine every year, and point the way toward developing it.

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Penicillin was once a “miracle” drug, but today medical professionals find a host of diseases—from staph infections to tuberculosis—evolving resistance to antibiotics. The origin of antibiotic-resistant organisms is a textbook example of natural selection. Patients infected with a diverse population of bacteria are given an antibiotic that wipes out almost all the bacteria. If they start to feel better and do not finish the full course of antibiotics, what is left behind are those bacteria most resistant to the drug. Those survivors then become the nucleus of a new, resistant population. Understanding this evolutionary process is an important part of modern public health.

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New drugs must be tested for a variety of safety factors, yet we cannot simply give unknown drugs to human test subjects and hope for the best. Because we know from evolution that we share a common ancestor with animals such as mice, dogs, and macaques, we can test drugs on these animals without endangering humans. The billions of dollars spent by pharmaceutical companies on animals testing depend on a practical application of evolution. Evolution has also helped scientists identify sources of lifesaving drugs. The Pacific Yew tree, for example, was once the only source of Taxol, a remarkable drug used to fight ovarian, lung, and breast cancer. This endangered tree grows very slowly, however, and 4-6 trees would be destroyed to produce just one dose of Taxol. Evolution came to rescue. Scientists used the evolutionary history of the Pacific Yew to trace back other trees in its family line, discovering Taxol-like compounds in more common trees. Evolution guided scientists in finding a replacement to the Pacific Yew, thus dramatically increasing the supply of Taxol available to cancer patients. Evolution saves lives.

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These are only a handful of the reasons why evolution is important to medicine. There are a host of other applications of evolution—agriculture, forensics, bioengineering. But the importance of evolution extends beyond its practical side; evolution explains the diversity of life on this planet, shows us our connection to other living things, and reveals profound insights into the processes of nature.

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Public’s Views on Human Evolution:

According to 2013 Pew Research Center analysis, six-in-ten Americans (60%) say that “humans and other living things have evolved over time,” while a third (33%) reject the idea of evolution, saying that “humans and other living things have existed in their present form since the beginning of time.” The share of the general public that says that humans have evolved over time is about the same as it was in 2009, when Pew Research last asked the question. About half of those who express a belief in human evolution take the view that evolution is “due to natural processes such as natural selection” (32% of the American public overall). But many Americans believe that God or a supreme being played a role in the process of evolution. Indeed, roughly a quarter of adults (24%) say that “a supreme being guided the evolution of living things for the purpose of creating humans and other life in the form it exists today.” These beliefs differ strongly by religious group. White evangelical Protestants are particularly likely to believe that humans have existed in their present form since the beginning of time. Roughly two-thirds (64%) express this view, as do half of black Protestants (50%). By comparison, only 15% of white mainline Protestants share this opinion. There also are sizable differences by party affiliation in beliefs about evolution, and the gap between Republicans and Democrats has grown. In 2009, 54% of Republicans and 64% of Democrats said humans have evolved over time, a difference of 10 percentage points. Today, 43% of Republicans and 67% of Democrats say humans have evolved, a 24-point gap. These are some of the key findings from a nationwide Pew Research Center survey conducted March 21-April 8, 2013, with a representative sample of 1,983 adults, ages 18 and older. The survey was conducted on landlines and cellphones in all 50 U.S. states and the District of Columbia. The margin of sampling error is +/- 3.0 percentage points.

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Figure above shows that while 98% of scientists connected to the American Association for the Advancement of Science say they believe humans evolved over time, only two-thirds (66%) of Americans overall perceive that scientists generally agree about evolution, according to 2014 data from a recent Pew Research Center survey on science and society. Those in the general public who reject evolution are divided on whether there is a scientific consensus on the topic, with 47% saying scientists agree on evolution and 46% saying they do not.

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Counter Creationists by logic and facts:

Despite definitive legal cases that have established the unconstitutionality of teaching intelligent design or creationist ideology in science class, the theory of evolution remains consistently under attack. It is not necessary or even possible to argue against “creationism” because creationism is a belief system based on faith. Science, on the other hand, is all about arguing about interpretation of observations and developing the best descriptions and explanations we can of the natural world. The political debate, not a scientific debate, between a religious belief system (creationism) and science (evolutionary biology), persisted through the 20th century and into the 21st century and it has been used by religious institutions and individuals as a tool. There is no longer a scientific debate about the validity of evolution, and there has not been one for a very long time.

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Historically, the strongest opposition to Darwinism, in the sense of being a synonym for the theory of evolution, has come from those advocating religious viewpoints. In essence, the chance component involved in the creation of new designs, which is inherent in the theory of evolution, runs counter to the concept of a Supreme Being who has designed and created humans and all phyla. Chance (stochastic processes) is centrally involved in the theory of evolution. As noted by Mayr (2001), chance plays an important role in two steps. First, the production of genetic variation “is almost exclusively a chance phenomenon.” Secondly, chance plays an important role even in “the process of the elimination of less fit individuals,” and particularly during periods of mass extinction. This element of chance counters the view that the development of new evolutionary designs, including humans, was a progressive, purposeful creation by a Creator God. According to the theory of evolution, creation of human beings was an accident, the end of a long, chance-filled process involving adaptations to local environments. There is no higher purpose, no progressive development, just natural forces at work. Such views are squarely at odds with many religious interpretations.

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However, natural selection is not “random” nor does it operate by “chance.” Natural selection preserves the gains and eradicates the mistakes. To illustrate this, imagine a monkey at a typewriter. In order for the monkey to type the first 13 letters of Hamlet’s soliloquy by chance, it would take 26^13 number of trials for success. This is 16 times as great as the total number of seconds that have elapsed in the lifetime of the solar system. But if each correct letter is preserved and each incorrect letter eradicated, the phrase “tobeornottobe” can be “selected for” in only 335 trials, or just seconds in a computer program. Richard Dawkins defines evolution as “random mutation plus nonrandom cumulative selection.” It is the cumulative selection that drives evolution. The eye evolved from a single, light sensitive spot in a cell into the complex eye of today not by chance, but through thousands of intermediate steps, each preserved because they made a better eye. Many of these steps still exist in nature in simpler organisms.

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Some creationists cite what they say is an incomplete fossil record as evidence for the failure of evolutionary theory. The fossil record was incomplete in Darwin’s time, but many of the important gaps that existed then have been filled by subsequent paleontological research. Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent.  Creationists’ demand for fossils that represent “missing links” reveals a deep misunderstanding of science. Nineteenth-century English social scientist Herbert Spencer made this prescient observation: “Those who cavalierly reject the Theory of Evolution, as not adequately supported by facts, seem quite to forget that their own theory is supported by no facts at all.”  Well over a century later nothing has changed. Creationists present not one fact in favor of creation and instead demand transitional fossil that proves evolution. We know evolution happened not because of transitional fossils such as A. natans but because of the convergence of evidence from such diverse fields as geology, paleontology, biogeography, comparative anatomy and physiology, molecular biology, genetics, and many more. No single discovery from any of these fields denotes proof of evolution, but together they reveal that life evolved in a certain sequence by a particular process.

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In fact, there are lots of intermediate fossils. Archaeopteryx, for example, is one of the earliest known fossil birds with a reptilian skeleton and feathers. There is now evidence that some dinosaurs had hair and feathers. Therapsids are the intermediates between reptiles and mammals, Tiktaalik is an extinct lobe-finned fish intermediate to amphibians, there are now at least six intermediate fossil stages in the evolution of whales, and in human evolution there are at least a dozen intermediate fossil stages since hominids branched off from the great apes seven million years ago. Considering the exceptionally low probability that a dead plant or animal will fossilize it is remarkable we have as many fossils as we do. First the dead animal has to escape the jaws of scavengers. Then is has to be buried under the rare circumstances that will cause it to fossilize instead of decay. Then geological forces have to somehow bring the fossil back to the surface to be discovered millions of years later by the handful of paleontologists looking for them.

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One of the finest compilations of evolutionary data and theory since Charles Darwin’s On the Origin of Species is Richard Dawkins’s magnum opus, The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution. Dawkins traces numerous transitional fossils (what he calls “concestors,” the last common ancestor shared by a set of species) from Homo sapiens back four billion years to the origin of heredity and the emergence of evolution. No single concestor proves that evolution happened, but together they reveal a majestic story of process over time.  No single fossil proves that dogs came from wolves, but archaeological, morphological, genetic and behavioral “fossils” converge to reveal the concestor of all dogs to be the East Asian wolf. The tale of human evolution is divulged in a similar manner (although here we do have an abundance of fossils), as it is for all concestors in the history of life. We know evolution happened because innumerable bits of data from myriad fields of science conjoin to paint a rich portrait of life’s pilgrimage

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Creationists say that if evolution happened gradually over millions of years, why doesn’t the Fossil Record show gradual change?

Sudden changes in the fossil record are not missing evidence of gradualism; they are extant evidence of punctuation. Species are stable over long periods of time and so they leave plenty of fossils in the strata while in their stable state. The change from one species to another, however, happens relatively quickly (on a geological time scale) in a process called punctuated equilibrium. One species can give rise to a new species when a small “founder” group breaks away and becomes isolated from the ancestral group. This new founder group, as long as it remains small and detached, may experience relatively rapid change (large populations are genetically stable). The speciational change happens so rapidly that few fossils are left to record it. But once changed into a new species, the individuals will retain their phenotype for a long time, leaving behind many well-preserved fossils. Millions of years later this process results in a fossil record that records mostly stability. The punctuation is there in between the equilibrium.

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Special creationists argue that “no one has seen evolution occur.” This misses the point about how science tests hypotheses. We don’t see Earth going around the sun or the atoms that make up matter. We “see” their consequences. Scientists infer that atoms exist and Earth revolves because they have tested predictions derived from these concepts by extensive observation and experimentation. Furthermore, on a minor scale, we “experience” evolution occurring every day. The annual changes in influenza viruses and the emergence of antibiotic-resistant bacteria are both products of evolutionary forces. Indeed, the rapidity with which organisms with short generation times, such as bacteria and viruses, can evolve under the influence of their environments is of great medical significance. Many laboratory experiments have shown that, because of mutation and natural selection, such microorganisms can change in specific ways from those of immediately preceding generations. On a larger scale, the evolution of mosquitoes resistant to insecticides is another example of the tenacity and adaptability of organisms under environmental stress. Similarly, malaria parasites have become resistant to the drugs that were used extensively to combat them for many years. As a consequence, malaria is on the increase, with more than 300 million clinical cases of malaria occurring every year. Creationist arguments are notoriously errant and based on a misunderstanding of evolutionary science and evidence.

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Evolution is a historical science confirmed by the fact that so many independent lines of evidence converge to this single conclusion. Independent sets of data from geology, paleontology, botany, zoology, biogeography, comparative anatomy and physiology, genetics, molecular biology, developmental biology, embryology, population genetics, genome sequencing, and many other sciences each point to the conclusion that life evolved. Hundreds of studies verify the facts of evolution, at both the microevolutionary and macroevolutionary scale—from the origin of new traits and new species to the underpinnings of the complexity we see in life and the statistical probability of such complexity arising. Creationists demand “just one fossil transitional form” that shows evolution. But evolution is not proved through a single fossil. It is proved through a convergence of fossils, along with a convergence of genetic comparisons between species, and a convergence of anatomical and physiological comparisons between species, and many other lines of inquiry. In fact we can see evolution happen—especially among organisms with short reproductive cycles that are subject to extreme environmental pressures. Knowledge of the evolution of viruses and bacteria is vital to medical science.

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Molecular evolutionary data counter a recent proposition called “intelligent design theory.” Proponents of this idea argue that structural complexity is proof of the direct hand of God in specially creating organisms as they are today. These arguments echo those of the 18th century cleric William Paley who held that the vertebrate eye, because of its intricate organization, had been specially designed in its present form by an omnipotent Creator. Modem-day intelligent design proponents argue that molecular structures such as DNA, or molecular processes such as the many steps that blood goes through when it clots, are so irreducibly complex that they can function only if all the components are operative at once. Thus, proponents of intelligent design say that these structures and processes could not have evolved in the stepwise mode characteristic of natural selection. However, structures and processes that are claimed to be “irreducibly” complex typically are not on closer inspection. For example, it is incorrect to assume that a complex structure or biochemical process can function only if all its components are present and functioning as we see them today. Complex biochemical systems can be built up from simpler systems through natural selection. Thus, the “history” of a protein can be traced through simpler organisms. Jawless fish have a simpler hemoglobin than do jawed fish, which in turn have a simpler hemoglobin than mammals. The evolution of complex molecular systems can occur in several ways. Natural selection can bring together parts of a system for one function at one time and then, at a later time, recombine those parts with other systems of components to produce a system that has a different function. Genes can be duplicated, altered, and then amplified through natural selection. The complex biochemical cascade resulting in blood clotting has been explained in this fashion. Similarly, evolutionary mechanisms are capable of explaining the origin of highly complex anatomical structures. For example, eyes may have evolved independently many times during the history of life on Earth. The steps proceed from a simple eye spot made up of light-sensitive retinula cells (as is now found in the flatworm), to formation of individual photosensitive units (ommatidia) in insects with light focusing lenses, to the eventual formation of an eye with a single lens focusing images onto a retina. In humans and other vertebrates, the retina consists not only of photoreceptor cells but also of several types of neurons that begin to analyze the visual image. Through such gradual steps, very different kinds of eyes have evolved, from simple light-sensing organs to highly complex systems for vision. Eyes evolved over many millions of years from simple organs that can detect light.

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Eager to discredit evolution, creationists ignore hominid fossil discoveries and cherry pick examples of hoaxes and mistakes in the belief that mistakes in science are a sign of weakness. This is a gross misunderstanding of the nature of science, which constantly advances by using both its mistakes and the successes. Its ability to build cumulatively on the past is how science progresses. The self-correcting feature of the scientific method is one of its most powerful assets. Hoaxes like Piltdown Man, and honest mistakes like Nebraska Man, Calaveras Man, and Hespero-pithecus, are, in time, corrected. In fact, it wasn’t creationists who exposed these errors, it was scientists who did so. Creationists simply read about the scientific exposé of these errors, and then duplicitously claimed them as their own.

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Current and future human evolution:

Humans are now able to modify our environments with technology. We have invented medical treatments, agricultural practices, and economic structures that significantly alter the challenges to reproduction and survival faced by modern humans. So, for example, because we can now treat diabetes with insulin, the gene versions that contribute to juvenile diabetes are no longer strongly selected against in developed countries. Some have argued that such technological advances mean that we’ve opted out of the evolutionary game and set ourselves beyond the reach of natural selection — essentially, that we’ve stopped evolving. However, this is not the case. Humans still face challenges to survival and reproduction, just not the same ones that we did 20,000 years ago. The direction, but not the fact of our evolution has changed. For example, modern humans living in densely populated areas face greater risks of epidemic diseases than did our hunter-gatherer ancestors (who did not come into close contact with so many people on a daily basis) — and this situation favors the spread of gene versions that protect against these diseases. Scientists have uncovered many such cases of recent human evolution.

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Are contemporary humans experiencing natural selection and evolving in response to it?

The answer to that question depends on whom one asks. A long tradition in the medical community holds that natural selection does not operate on contemporary human populations because medicine keeps “alive many who otherwise would have perished”. No evolutionary biologist would now agree with that claim, for natural selection works through differential reproductive success rather than simple differential survival, and individuals in contemporary human populations vary in lifetime reproductive success (LRS). Selection operates on any trait that varies and is correlated with LRS, and traits respond to selection with change across generations if they vary genetically. But what traits is selection operating on? Do they include the traits treated by physicians? Previous work has shown that human life history traits, most significantly age at first reproduction, are currently under selection, but evidence for selection operating on traits of medical importance is scarce.

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The British geneticist Steve Jones has given a lecture at University College London entitled “Is human evolution over?”  His answer to his own question is in the affirmative.  His argument is that human evolution, at least in the western societies, has stopped or slowed down because very few older men in such societies reproduce.  Sperm of older men carry many more mutations than those of younger men.  Mutations provide the source of genetic variations on which natural selection works.  Hence, no older fathers, no genetic mutations, no evolution. Jones also argues that the human species is nearing the end of its capacity for change. He uses as an example the length of the average human life, which increased encouragingly over the last century as a result of improved sanitation, better nutrition, and immunization. Lately, though, this increase seems to have reached a limit. If we can’t be improved any further, he says, then evolution must really have come to a stop for us.

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There are two things wrong with this argument. First, it implies that evolution must result in improvement. Species evolve in response to whatever environment they encounter–if short lives were advantageous, shorter life spans would be selected for. Second, Jones confuses changes in our life spans that can be traced to alterations in the environment, such as better hygiene, with changes owing to our genes. It is not true that we are running out of the genetic potential to increase (or decrease) our life span. No despots have ever set out to select for increased or decreased longevity in the populations they control. If they did, the experiment would doubtless work. We already know it works with mice, some strains of which have been bred to have nearly twice the normal mouse life span and others only half. In this regard, humans are no different from the pigs, cattle, and wheat that our farmers subject to artificial selection. As a species we harbour ample amounts of genetic variation on which selection, either natural or artificial, can act. This variation comes ultimately from mutations in our genes, the stretches of DNA that code for proteins. Researchers estimate that each individual human inherits some 60 genetic mutations not found in either parent—an average of one mutation for every 100 million nucleotides.  Since there are more than 7 billion people on Earth, that means there are at least 420 billion new mutations flooding into the total human gene pool every generation–adding to the billions and billions of mutant genes that are already there. Many have no immediate consequence, some are catastrophic, and a tiny fraction are beneficial.  Luckily for our species, natural selection is continually sorting out this flood, retaining good mutations, removing bad ones. Because most have slight effects, the selection process is largely invisible. If you carry a gene that reduces by 1 percent the likelihood of your having children, you are unlikely to notice its effects. Even so, this weak selection is enough to reduce the frequency of the gene in the population over time. Indeed, once the gene is rare enough, it might be eliminated entirely if all its carriers fail by chance to reproduce. Conversely, if a new mutant gene increases by 1 percent the likelihood that you will have children, chances are it will stealthily spread through the population. Evolution is going on invisibly all the time.

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Adaptive evolution in the human genome:

Adaptive evolution results from the propagation of advantageous mutations through positive selection. This is the modern synthesis of the process which Darwin and Wallace originally identified as the mechanism of evolution. However, in the last half century there has been considerable debate as to whether evolutionary changes at the molecular level are largely driven by natural selection or random genetic drift. Unsurprisingly, the forces which drive evolutionary changes in our own species’ lineage have been of particular interest. Quantifying adaptive evolution in the human genome gives insights into our own evolutionary history and helps to resolve this neutralist-selectionist debate. Identifying specific regions of the human genome that show evidence of adaptive evolution helps us find functionally significant genes, including genes important for human health, such as those associated with diseases.

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Regions of the genome which show evidence of adaptive evolution:

A considerable number of studies have used genomic methods to identify specific human genes that show evidence of adaptive evolution. Table below gives selected examples of such genes for each gene type discussed, but provides nowhere near an exhaustive list of the human genes showing evidence of adaptive evolution.

Type of gene Gene name Phenotype produced by gene/Region where gene expressed Study
Disease ASPM Microcephaly (characterised by small head and mental retardation) Mekel-Bobrov et al. 2005
Disease HYAL3 Cancers, tumour suppression Nielsen et al. 2005a
Disease DISC1 Schizophrenia Crespi et al. 2007
Immune CD72 Immune system signalling Nielsen et al. 2005a
Immune IGJ Links immunoglobulin monomers Williamson et al. 2007
Immune PTCRA Pre T-cell antigen receptor Bakewell et al. 2007
Testes USP26 Testes specific expression Nielsen et al. 2005a
Testes RSBN1 Protein structure of sperm Voight et al. 2006
Testes SPAG5 Sperm associated antigen 5 Bakewell et al. 2007
Olfactory OR2B2 Olfactory receptor Nielsen et al. 2005a
Olfactory OR4P4 Olfactory receptor Williamson et al. 2007
Olfactory OR10H3 Olfactory receptor 10H3 Bakewell et al. 2007
Nutrition LCT Lactose metabolism Williamson et al. 2007
Nutrition NR1H4 Nuclear hormone receptor related to phenotypes including bile acid and lipoprotein Williamson et al. 2007
Nutrition SLC27A4 Uptake of fatty acids Voight et al. 2006
Pigmentation OCA2 Lightened skin Voight et al. 2006
Pigmentation ATRN Skin pigmentation Willamson et al. 2007
Pigmentation TYRP1 Lightened skin Voight et al. 2006

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Humans are still Evolving:

When we think of human evolution, our minds wander back to the thousands of years it took natural selection to produce the modern-day man. But are we still changing as a species, even today? New research suggests that, despite modern technology and industrialization, humans continue to evolve. “It is a common misunderstanding that evolution took place a long time ago, and that to understand ourselves we must look back to the hunter-gatherer days of humans,” says Dr. Virpi Lummaa from the University of Sheffield’s department of animal and plant sciences. But not only are we still evolving, we’re doing so even faster than before. In the last 10,000 years, the pace of our evolution has sped up 100 times, creating more mutations in our genes, and more natural selections from those mutations. Here are some clues that show humans are continuing to evolve.

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  1. We drink Milk:

Historically, the gene that regulated a human’s ability to digest lactose shut down as they were weaned off of their mother’s breast milk. But when we began domesticating cows, sheep and goats, being able to drink milk became a nutritionally advantageous quality, and people with the genetic mutation that allowed them to digest lactose were better able to propagate their genes. A 2006 study suggests this tolerance for lactose was still developing as early as 3,000 years ago in East Africa. That genetic mutation for digesting milk is now carried by more than 95 percent of Northern European descendants.

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  1. We’re losing our Wisdom Teeth:

Our ancestors had much bigger jaws than we do, which helped them chew a tough diet of roots, nuts and leaves. And what meat they ate they tore apart with their teeth, all of which led to worn down teeth that needed replacing. Enter the wisdom teeth: A third set of molars is believed to be the evolutionary answer to accommodate our ancestors’ eating habits. Today, we have utensils to cut our food. Our meals are softer and easier to chew, and our jaws are much smaller as a result, which is why wisdom teeth are often impacted when they come in — there just isn’t room for them. Like the appendix, wisdom teeth have become vestigial organs. One estimate says 35 percent of the population is born without wisdom teeth, and some say they will disappear altogether.

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  1. We’re resisting Diseases:

In 2007, a group of researchers looking for signs of recent evolution uncovered 1,800 genes that have only become prevalent in humans in the last 40,000 years, many of which are devoted to fighting infectious diseases like malaria. More than a dozen new genetic variants for fighting malaria are spreading rapidly among Africans. Another study found that natural selection has favored city-dwellers. Living in cities has produced a genetic variant that allows us to be more resistant to diseases like tuberculosis and leprosy. “This seems to be an elegant example of evolution in action,” says Dr. Ian Barnes from the School of Biological Sciences at Royal Holloway. “It flags up the importance of a very recent aspect of our evolution as a species, the development of cities as a selective force.”

Malaria:

In regions where malaria is endemic, anyone with a genotype giving resistance to malaria would be at an advantage in evolutionary terms, because they would be more likely to survive and reproduce, passing their advantageous combination of genes on to at least some of their children. The overlap between the geographic spread of malaria in Africa with the presence of the sickle-cell allele is an example: individuals heterozygous for this allele are at a selective advantage over unaffected individuals (and those homozygous for the allele) where malaria is present.

CCR5:

The “CCR5” gene is another example. This gene codes for CCR5, a surface protein on white blood cells that is also the docking site for the HIV virus. People homozygous for the ‘delta 32’ mutation in this gene are resistant to attack by HIV, and so they are at a selective advantage in populations where HIV infection (and AIDS) is common. But surprisingly the mutation is most common in white Europeans, and very rare in other ethnic groups, including Africans. AIDS is far more common in Africa than in Europe, so these differences in allele frequency are difficult to explain, unless they are the result of some other selective pressure that predates the AIDS epidemic. Scientists have dated the origin of the delta 32 mutation to around 700 years ago, and the current hypothesis is that it provided protection against an epidemic disease of that time, perhaps plague or smallpox.

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  1. Our brains are shrinking:

While we may like to believe our big brains make us smarter than the rest of the animal world, our brains have actually been shrinking over the last 30,000 years. The average volume of the human brain has decreased from 1,500 cubic centimeters to 1,350 cubic centimeters, which is equivalent to a chunk the size of a tennis ball. There are several different conclusions as to why this is: One group of researchers suspects our shrinking brains mean we are in fact getting dumber. Historically, brain size decreased as societies became larger and more complex, suggesting that the safety net of modern society negated the correlation between intelligence and survival. But another, more encouraging theory says our brains are shrinking not because we’re getting dumber, but because smaller brains are more efficient. This theory suggests that, as they shrink, our brains are being rewired to work faster but take up less room. There’s also a theory that smaller brains are an evolutionary advantage because they make us less aggressive beings, allowing us to work together to solve problems, rather than tear each other to shreds.

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  1. We have Blue Eyes:

Originally, we all had brown eyes. But about 10,000 years ago, someone who lived near the Black Sea developed a genetic mutation that turned brown eyes blue. While the reason blue eyes have persisted remains a bit of a mystery, one theory is that they act as a sort of paternity test. “There is strong evolutionary pressure for a man not to invest his paternal resources in another man’s child,” says the lead author of a study on the development of our baby blues. Because it is virtually impossible for two blue-eyed mates to create a brown-eyed baby, our blue-eyed male ancestors may have sought out blue-eyed mates as a way of ensuring fidelity. This would partially explain why, in a recent study, blue-eyed men rated blue-eyed women as more attractive compared to brown-eyed women, whereas females and brown-eyed men expressed no preference.

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  1. New traits:

Researchers have found tell-tale signs of newly evolved traits like immunity from some infectious diseases, increased tolerance of ultraviolet radiation from sunlight, the ability to handle specific dietary changes, and tolerance for low-oxygen in mountainous environments.

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  1. Birth patterns:

Population records, like those kept by governments and churches, show that changes in the timing of life events, like births and deaths, have continued to evolve through natural selection. A common theme in such studies is that natural selection favors women who become mothers at an earlier age. Women who have children at a younger age tend to have more children over the span of their lifetime. This evolutionary pressure to reproduce at a younger age conflicts with societal trends toward delaying reproduction and highlights why we need to better understand how evolution is progressing—cultural and evolutionary forces can act in opposition to one another.

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  1. Heart data:

The Framingham Heart Study continues today, with three generations of participants contributing to what has become the longest-running multigenerational study in medical history. Yet the Framingham data speak to more than just cardiovascular health. They have shown that people (specifically, women) with lower total cholesterol levels and lower systolic blood pressures tend to have more children, who inherit their genes for these traits. Over generations, this means that those traits will become more and more common. In other words, the population is evolving.

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  1. It has also been shown that height and body mass index (BMI) have been under selection in Europeans.

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People commonly assume that our species has evolved very little since prehistoric times. Yet new studies using genetic information from populations around the globe suggest that the pace of human evolution increased with the advent of agriculture and cities.

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In a study published in 2007 Henry C. Harpending of the University of Utah, John Hawks of the University of Wisconsin–Madison and their colleagues analyzed data from the international haplotype map of the human genome. They focused on genetic markers in 270 people from four groups: Han Chinese, Japanese, Yoruba and northern Europeans. They found that at least 7 percent of human genes underwent evolution as recently as 5,000 years ago. Much of the change involved adaptations to particular environments, both natural and human-shaped. For example, few people in China and Africa can digest fresh milk into adulthood, whereas almost everyone in Sweden and Denmark can. This ability presumably arose as an adaptation to dairy farming.

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Another study by Pardis C. Sabeti of Harvard University and her colleagues used huge data sets of genetic variation to look for signs of natural selection across the human genome. More than 300 regions on the genome showed evidence of recent changes that improved people’s chance of surviving and reproducing. Examples included resistance to one of Africa’s great scourges, the virus causing Lassa fever; partial resistance to other diseases, such as malaria, among some African populations; changes in skin pigmentation and development of hair follicles among Asians; and the evolution of lighter skin and blue eyes in northern Europe.

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Harpending and Hawks’s team estimated that over the past 10,000 years humans have evolved as much as 100 times faster than at any other time since the split of the earliest hominid from the ancestors of modern chimpanzees. The team attributed the quickening pace to the variety of environments humans moved into and the changes in living conditions brought about by agriculture and cities. It was not farming per se or the changes in the landscape that conversion of wild habitat to tamed fields brought about but the often lethal combination of poor sanitation, novel diet and emerging diseases (from other humans as well as domesticated animals). Although some researchers have expressed reservations about these estimates, the basic point seems clear: humans are first-class evolvers.

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mtDNA and recent human evolution:

A recent study (Ruiz-Pesini et al. 2004) of mtDNA has demonstrated that gene frequencies have changed over the last 50,000 years i.e. human populations have still been subject to evolution. Some mutations in mtDNA may make aerobic respiration less efficient, so that the mitochondria generate more heat and less ATP. These mutations will be selected for if they are beneficial to the person carrying them – and they would certainly be advantageous for humans living in the cold climates that prevailed during the Ice Age. Examination of the mtDNA from over 1,000 people has found that such a mutation is present in populations of Northern Europeans, East Asians, and Amerindians. Of those in the sample that live in Arctic regions, 75% had the mutation, which was also found in the 14% of the sample living in temperate zones. Some of the ancestors of these groups would have lived in Siberia, and all would have experienced the Ice Age’s glacial conditions. However, the mutation is not found at all in people of African ancestry. The study concludes that the correlation between habitat and presence of the beneficial mutation is evidence of positive selection for the changed gene sequence. That is, the mutation was selected for because those people who had them were able to generate more body heat in an extremely cold climate.

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Still evolving, Human genes tell New Story a 2006 study:

Providing the strongest evidence yet that humans are still evolving, researchers have detected some 700 regions of the human genome where genes appear to have been reshaped by natural selection, a principal force of evolution, within the last 5,000 to 15,000 years. The genes that show this evolutionary change include some responsible for the senses of taste and smell, digestion, bone structure, skin color and brain function. Many of these instances of selection may reflect the pressures that came to bear as people abandoned their hunting and gathering way of life for settlement and agriculture, a transition well under way in Europe and East Asia some 5,000 years ago. Under natural selection, beneficial genes become more common in a population as their owners have more progeny. Three populations were studied, Africans, East Asians and Europeans. In each, a mostly different set of genes had been favored by natural selection. The selected genes, which affect skin color, hair texture and bone structure, may underlie the present-day differences in racial appearance. The study of selected genes may help reconstruct many crucial events in the human past. It may also help anthropologists explain why people over the world have such a variety of distinctive appearances, even though their genes are on the whole similar. The finding adds substantially to the evidence that human evolution did not grind to a halt in the distant past, as is tacitly assumed by many social scientists. Even evolutionary psychologists, who interpret human behavior in terms of what the brain evolved to do, hold that the work of natural selection in shaping the human mind was completed in the pre-agricultural past, more than 10,000 years ago. “There is ample evidence that selection has been a major driving point in our evolution during the last 10,000 years, and there is no reason to suppose that it has stopped,” said Jonathan Pritchard, a population geneticist at the University of Chicago who headed the study.

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Genetic evidence for natural selection in humans in the contemporary United States a 2016 study:

Recent findings from molecular genetics now make it possible to test directly for natural selection by analyzing whether genetic variants associated with various phenotypes have been under selection. Author leverage these findings to construct polygenic scores that use individuals’ genotypes to predict their body mass index, educational attainment (EA), glucose concentration, height, schizophrenia, total cholesterol, and (in females) age at menarche. He then examines associations between these scores and fitness to test whether natural selection has been occurring. His study sample includes individuals of European ancestry born between 1931 and 1953 who participated in the Health and Retirement Study, a representative study of the US population. The results imply that natural selection has been slowly favoring lower EA in both females and males, and are suggestive that natural selection may have favored a higher age at menarche in females. For EA, estimates imply a rate of selection of about −1.5 months of education per generation (which pales in comparison with the increases in EA observed in contemporary times). Although they cannot be projected over more than one generation, the results provide additional evidence that humans are still evolving—albeit slowly, especially compared with the rapid changes that have occurred over the past few generations due to cultural and environmental factors.

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Humans are still evolving, say scientists in 2017 study:

While there is overwhelming evidence for human evolution and unequivocal footprints of adaptation in the genome, rarely have scientists been able to directly observe natural selection operating in people. As a result, biologists still understand very little about the workings of natural selection in humans. Authors’ basic idea was that mutations that lower the chance of survival should be present at lower frequency in older individuals. For example, if a mutation becomes harmful at the age of 60 years, people who carry it have a lower chance to survive past 60 – and the mutation should be less common among those who live longer than that. Authors therefore looked for mutations that change in frequency with age among around 60,000 individuals from California (part of the GERA cohort) and around 150,000 from the U.K. Biobank. To avoid the complication that people whose ancestors lived in different places carry a somewhat different set of mutations, they focused on the largest group with shared ancestry within each study.

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Across the genome, they found two variants that endanger survival. The first is a variant of the APOE gene, which is a well-known risk factor for Alzheimer’s disease. It drops in frequency beyond age 70. The second harmful variant we found is a mutation in the CHRNA3 gene. Associated with heavy smoking, this inherited mutation starts to decrease in frequency at middle age in men, because carriers of this mutation are less likely to survive longer. Both deleterious variants only had an effect long after the typical ages of reproduction for both females and males. Biologists usually consider such mutations to not be under selection. After all, by late middle age, most people have already passed their genes on to whatever offspring they’ll have, so it seems like it might not matter how long they live beyond that point. Why then would authors only find two, when their study was large enough to detect any such variant, if common in the population? One possibility is that mutations that only imperil survival so late in life almost never arise. While that is possible, the genome is a large place, so that seems unlikely. The other intriguing possibility is that natural selection prevents even late-acting variants from becoming common in the population by natural selection, if they have large enough effects. Why might that be? For one, men can father children in old age. Even if only a tiny fraction of them do so, it may be enough of an evolutionary fitness cost for selection to act on. Survival beyond the age of reproduction could also be beneficial for the survival of related individuals who carry the same mutations, most directly children. In other words, surviving past typical reproductive ages may be beneficial for humans after all. Perhaps more surprisingly, they discovered that people who carry mutations that delay puberty or the age at which they have their first child tend to live longer. It was known from epidemiological studies that early puberty is associated with adverse effects later in life such as cancer and obesity. The results indicate some of that effect is probably due to heritable factors. So humans carry common mutations that affect their survival and natural selection appears to act on at least a subset, in some contemporary environments.

Bottom line: Comparing genomes of more than 200,000 people, researchers identified genetic variants that are less common in older people, suggesting natural selection continues to weed out disadvantageous traits.

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Human activated evolution:

Since humans often cause major changes in the environment, we are frequently the instigators of evolution in other organisms.

Here are a few examples of human-caused evolution:

  1. Several species have evolved in response to climate change.
  2. Fish populations have evolved in response to our fishing practices.
  3. Insects like bedbugs and crop pests have evolved resistance to our pesticides.
  4. Bacteria, HIV, malaria, and cancer have evolved resistance to our drugs.

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Artificial selection:

Artificial selection is the selective breeding of animals or plants by humans to modify an organism. The term artificial selection implies a process affecting evolution the same way as natural selection, but due to human activity as opposed to natural processes. An example is the evolution of dogs from wolves; this happened over many millennia, beginning in the Stone Age. Humans would tolerate a companion wolf that happened to be non-threatening, but not one that was aggressive. Being more friendly to humans thus became a survival advantage, so gradually dogs branched off from wolves. Stone Age humans weren’t creating dogs consciously, at least not at first, but once they had a population of docile wolves, their value as look-outs, vermin hunters, and shepherds was exploited and the population was shaped further. In more recent centuries, humans have purposely bred dogs into numerous varieties for specific jobs or purely for personal enjoyment. Humans have similarly domesticated many other animals including horses, cows, goats, sheep, llamas, and so on. This, along with many plant species, marked the invention of agriculture and brought humanity into the modern era. Modification of organisms for food continues to this day.

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Research suggests that such artificial selection is happening at least in the context of two common procedures in obstetrics and gynaecology: caesarean section and abortion.

  1. Caesarean section, or surgical birth, is where a fetus is delivered through surgical incisions made through the abdominal wall and through the uterus. This is in contrast to vaginal birth that evolved in nature where the infant comes out through the birth canal. From the time that the human brain started to increase dramatically in size in early hominids until the early 20th century, the constraints of vaginal birth put limits on how big a fetal head could grow and how narrow a female pelvis could be. Either a fetal head too big or a maternal pelvis too narrow would mean that one or both individuals would die and the genes responsible for those traits would die with them.

Cephalopelvic disproportion (CPD) is what doctors call the condition when the fetal head is too big compared with the size of the mother’s pelvis. The chances of developing CPD depend greatly on the mother’s genetic tendency to develop a narrow pelvis. 200 years ago, if a pregnancy was in a state of CPD, the woman and fetus would die, since the head could not get through the birth canal. Remembering that all organisms experience random mutations and spontaneous diversity in all traits, occasionally a genetic tendency toward CPD will develop. Tragically, these random mutations will not persist because they end up being lethal, either to a mother or to her potential offspring.

Around 1900, however, surgeons were perfecting their ability to bypass the birth canal altogether. This involved accessing the uterus through the abdomen, delivering the child, and repairing the wounds without the mother bleeding to death in the process. The result is that the CPD condition would not have to be fatal. In the developed world, surgical birth has been increasing dramatically since the 1960s. Today, some countries have a caesarean rate as high as 40 percent. In a sense, the invention of surgical birth has removed the intense selective pressure constraining the size of both the fetal cranium and the female pelvis. It is likely that, humans being the diversity-generation machines that we are, larger fetal heads and smaller female pelvises could arise via spontaneous mutations.

But has the removal of selective pressure of the birth canal actually enabled changes in the size of the cranium and hips? For the past several decades, physicians have been monitoring head circumference from birth through early childhood, because it is very much related to developmental problems. Both microcephaly (small head circumference) and macrocephaly (very large head circumference) are connected with a variety of physical and mental abnormalities. Based on these observations, there is no evidence of an increase in head or brain size in medically normal humans in the era of surgical birth. On the other hand, the increase in surgical births since the 1960s has been correlated with an increase in narrow hips in females, so we can anticipate more women with narrow hips in the decades to come. This really means increasing genetic disposition for narrow hips in the human gene pool.

  1. The flip side to caesarean section is elective abortion. Combined with genetic counselling, intentional termination of pregnancy appears to be producing a noticeable decrease in the number of children born in Middle Eastern countries with a genetic blood disorder called thalassemia. Screening and counselling are intended to discourage marriages between thalassemia carriers – individuals with a genetic makeup that’s part normal and part thalassemia. These individuals may or may not have mild symptoms of the disease. In practice, however, few marriages are discouraged; instead, parents tend to opt for abortion when prenatal screening shows that fetus would suffer from severe thalassemia, or in many cases thalassemia of intermediate severity. As a result, the frequency of thalassemia genes is on the decline in certain Middle Eastern countries. This is happening despite the fact that thalassemia carriers resist malaria, just like carriers of the sickle cell gene. This means that genetic counselling and abortion are affecting thalassemia genes more than malaria is affecting those genes. Most likely, this is because malaria has been on the decline for the past few decades in certain Middle Eastern countries, Turkey for instance.

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Mate selection:

When it comes to choosing mates (as opposed to simply living long enough to mate), the consequence is not life or death, but selection is still operating. The classic example in the animal kingdom is the male peacock, a bird that attracts a mate with a beautiful, colorful plume. Those that are less fit – males that lack a colorful plume – may not pass on their genes, so natural selection is widely in play even if an unmated peacock lives to a ripe old age. Do factors like hairstyles, makeup, clothing, and development of an attractive physique through exercise produce a similar effect in people? University of New Mexico evolutionary psychologist Geoffrey Miller thinks that sexual selection may currently be a major factor in human evolution. Mastering increasing technology requires increasing intelligence, so intelligence leads both to economic and social success, including mating. To be sure, mate selection for a relationship such as marriage does not equal reproduction, as people can reproduce with mates they choose on a whim for a brief encounter. Applied statistically to a population, however, the factors that Miller has considered may produce a noticeable effect on the gene pool. If the effect actually occurs then it would be an example of natural selection shaping the human gene pool.

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Future evolution:

Future Evolution is a book written by paleontologist Peter Ward and illustrated by Alexis Rockman. He addresses his own opinion of future evolution and compares it with Dougal Dixon’s After Man: A Zoology of the Future and H. G. Wells’s The Time Machine. According to Ward, humanity may exist for a long time. Nevertheless, we are impacting our world. He splits his book in different chronologies, starting with the near future (the next 1,000 years). Humanity would be struggling to support a massive population of 11 billion. Global warming raises sea levels. The ozone layer weakens. Most of the available land is devoted to agriculture due to the demand for food. Despite all this, the oceanic wildlife remains untethered by most of these impacts, specifically the commercial farmed fish. This is, according to Ward, an era of extinction that would last about 10 million years (note that many human-caused extinctions have already occurred). After that, the world gets stranger. Ward labels the species that have the potential to survive in a human-infested world. These include dandelions, raccoons, owls, pigs, cattle, rats, snakes, and crows to name but a few. In the human-infested ecosystem, those preadapted to live amongst man survived and prospered. Ward describes garbage dumps in the future infested with multiple species of rats, a snake with a sticky frog-like tongue to snap up rodents, and pigs with snouts specialized for rooting through garbage. The story’s time traveller who views this new refuse-covered habitat is gruesomely attacked by ravenous flesh-eating crows. Ward then questions the potential for humanity to evolve into a new species. According to him, this is incredibly unlikely. For this to happen a human population must isolate itself and interbreed until it becomes a new species. Then he questions if humanity would survive or extinguish itself by climate change, nuclear war, disease, or the posing threat of nanotechnology as terrorist weapons.

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Did humans really descend from apes?

Since Charles Darwin published the theory of evolution by means of natural selection in 1859, myths and misinterpretations have eroded public understanding of his ideas.  One of the most persistent myths concerns the relationship of humans to great apes, a group of primates that includes the gorilla, orangutan and chimpanzee. Someone who believes the myth will say, “If evolution exists, then humans must be descended directly from apes. Apes must have changed, step by step, into humans.” This same person will often follow up with this observation: “If apes ‘turned into’ humans, then apes should no longer exist.” Although there are several ways to attack this assertion, the bottom-line rebuttal is simple — humans didn’t descend from apes. That’s not to say humans and apes aren’t related, but the relationship can’t be traced backward along a direct line of descent, one form morphing into another. It must be traced along two independent lines, far back into time until the two lines merge. The intersection of the two lines represents something special, what biologists refer to as a common ancestor. This apelike ancestor, which probably lived 5 to 11 million years ago in Africa, gave rise to two distinct lineages, one resulting in hominins — humanlike species — and the other resulting in the great ape species living today. Or, to use a family tree analogy, the common ancestor occupied a trunk, which then divided into two branches. Hominins developed along one branch, while the great ape species developed along another branch.

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Human features – are we unique or are we immature apes?

Humans possess the same general features of mammals, primates and apes but we also differ in many ways. Some of these differences are physical while others are behavioural.

Physical features that are commonly used to separate humans from our closest ape relatives include:

  • rounded braincase with thin skull bones
  • high, vertical forehead
  • vertical face
  • small brow ridges
  • short jaws
  • centrally located foramen magnum (the hole in the base of the skull through which the spinal cord runs)
  • skull balanced on a vertical backbone
  • reduced hairiness

The physical features listed above are, however, also found in baby chimpanzees and other immature apes, which suggests that human evolution has involved the retention of juvenile features within adults. This evolutionary process is called neoteny.

Although many features of the human skull are reflected in the skulls of immature apes, many other features are unique to humans. These include:

  • extremely large brains relative to our body size
  • body structure that enables sustained movement on two legs (bipedalism)
  • short, blunt canine teeth
  • eruption of the canine teeth before the premolar teeth
  • projecting chin
  • speech
  • extremely sparse cover of body hair but a dense hair cover on the head
  • permanent enlargement of female breasts when mature
  • relatively short, straight finger and toe bones
  • long thumb that enables a precision grip
  • average life span that is longer than that of other apes
  • a lengthy period of development after weaning and a prolonged adolescence
  • complex tools are made and used
  • art, music, writing and other symbols
  • burial of the dead
  • transmission of cultural ideas, meanings and behaviours from one generation to the next
  • worldwide distribution

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The first apes evolved about 25 million years ago and by 20 million years ago were a very diverse group. Within the last 10 million years, however, many ape species became extinct as the earth’s climate cooled and dried and their forested environments changed to woodland and grassland. There are now only about 20 living species of apes and they are divided into two major groups. These are the:

  • Lesser Apes, containing the gibbons
  • Great Apes, containing the orang-utans, gorillas, chimpanzees and humans

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Humans are classified in the sub-group of primates known as the Great Apes. Humans have bodies that are genetically and structurally very similar to those of the Great Apes and so we are classified in the Great Apes sub-group which is also known as the hominids (Family Hominidae). The genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids (great apes) branch of the primates. The closest living relatives of humans are chimpanzees (genus Pan) and gorillas (genus Gorilla). With the sequencing of the human and chimpanzee genomes, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 96%. By using the technique called a molecular clock which estimates the time required for the number of divergent mutations to accumulate between two lineages, the approximate date for the split between lineages can be calculated. The gibbons (family Hylobatidae) and orangutans (genus Pongo) were the first groups to split from the line leading to the humans, then gorillas (genus Gorilla) followed by the chimpanzees (genus Pan). The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch. During this split, chromosome 2 was formed from two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. Modern humans, defined as the species Homo sapiens or specifically to the single extant subspecies Homo sapiens sapiens, proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000–60,000 years ago, Australia around 40,000 years ago, the Americas around 15,000 years ago, and remote islands such as Hawaii, Easter Island, Madagascar, and New Zealand between the years 300 and 1280.

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Humans are similar to great apes:

Figure above shows similarities of apes and human.

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Chimpanzee–human last common ancestor:

There are two living species of chimpanzee – the Common Chimpanzee, Pan troglodytes, and the Bonobo or Pygmy Chimpanzee, Pan paniscus. Chimpanzees live in woodland and forests in western and central tropical Africa. Chimpanzees are the smallest of the Great Apes and our closest living relatives. Chimpanzees struggle for status, vocalise, communicate, play politics, use subterfuge, show aggression, reject outsiders, groom and support each other, betray each other and resort to violence or sexual bribery to get their way. Chimpanzees display awareness of self, ability to reason, and a grasp of numbers. Chimpanzees are opportunistic omnivores that also make and use tools for gain, and groups of chimpanzees in the wild have separate traditions, practices and ways of doing things that they pass down the generations. That is, chimpanzees have culture. Chimpanzees and humans have a genetic kinship so close that they share almost 96% of their DNA. The chimpanzee–human last common ancestor, or CHLCA, is the last common ancestor shared by the extant Homo (human) and Pan (chimpanzee) genera of Hominini. Due to complex hybrid speciation, it is not possible to give a precise estimate on the age of this ancestral individual. While “original divergence” between populations may have occurred as early as 13 million years ago (Miocene), hybridization may have been ongoing until as recent as 4 million years ago (Pliocene). Speciation from Pan to Homo appears to have been a long, drawn-out process. After the original divergences, there were, according to Patterson (2006), periods of hybridization between population groups and a process of alternating divergence and hybridization that lasted several million years. Sometime during the late Miocene or early Pliocene, the earliest members of the human clade completed a final separation from the lineage of Pan — with date estimates ranging from 13 million to as recent as 4 million years ago. Richard Wrangham (2001) argued that the CHLCA species was very similar to the common chimpanzee (Pan troglodytes) — so much so that it should be classified as a member of the Pan genus and be given the taxonomic name Pan prior. However, no fossil has yet been identified as a probable candidate for the CHLCA or the taxon Pan prior. In human genetic studies, the CHLCA is useful as an anchor point for calculating single-nucleotide polymorphism (SNP) rates in human populations where chimpanzees are used as an outgroup, that is, as the extant species most genetically similar to Homo sapiens. Chimpanzees offer scientists an unmatched view of what distinguishes humanity from its apelike ancestors. Based on evidence from the hominin fossil record and extensive morphological, developmental, and genetic data, Chimpanzees and Human Evolution makes the case that the last common ancestor of chimpanzees and humans was chimpanzee-like. It most likely lived in African rainforests around eight million years ago, eating fruit and walking on its knuckles.

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Missing link: Evidence from the fossil record:

For sceptical contemporaries of Darwin, the “missing link”—the absence of any known transitional form between apes and humans—was a battle cry, as it remained for uninformed people afterward. Not one but many creatures intermediate between living apes and humans have since been found as fossils. The oldest known fossil hominins—i.e., primates belonging to the human lineage after it separated from lineages going to the apes—are 6 million to 7 million years old, come from Africa, and are known as Sahelanthropus and Orrorin (or Praeanthropus), which were predominantly bipedal when on the ground but which had very small brains. Ardipithecus lived about 4.4 million years ago, also in Africa. Numerous fossil remains from diverse African origins are known of Australopithecus, a hominin that appeared between 3 million and 4 million years ago. Australopithecus had an upright human stance but a cranial capacity of less than 500 cc (equivalent to a brain weight of about 500 grams), comparable to that of a gorilla or a chimpanzee and about one-third that of humans. Its head displayed a mixture of ape and human characteristics—a low forehead and a long, apelike face but with teeth proportioned like those of humans. Other early hominins partly contemporaneous with Australopithecus include Kenyanthropus and Paranthropus; both had comparatively small brains, although some species of Paranthropus had larger bodies. Paranthropus represents a side branch in the hominin lineage that became extinct. Along with increased cranial capacity, other human characteristics have been found in Homo habilis, which lived about 1.5 million to 2 million years ago in Africa and had a cranial capacity of more than 600 cc (brain weight of 600 grams), and in H. erectus, which lived between 0.5 million and more than 1.5 million years ago, apparently ranged widely over Africa, Asia, and Europe, and had a cranial capacity of 800 to 1,100 cc (brain weight of 800 to 1,100 grams). The brain sizes of H. ergaster, H. antecessor, and H. heidelbergensis were roughly that of the brain of H. erectus, some of which species were partly contemporaneous, though they lived in different regions of the Eastern Hemisphere. (See also human evolution.)

Five hominins—members of the human lineage after it separated at least seven million to six million years ago from lineages going to the apes—are depicted in an artist’s interpretations above. All but Homo sapiens, the species that comprises modern humans, are extinct and have been reconstructed from fossil evidence.

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Molecular comparison between humans and apes:

Developments in biochemistry and immunology during the first half of the 20th century enabled the search for evidence of the relationships between modern humans and the apes to shift from macroscopic morphology to the morphology of molecules. The results of applying a new generation of analytical methods to proteins were reported by the Austrian-born French biologist Emile Zuckerkandl and American biologist Morris Goodman in the early 1960s. Zuckerkandl used enzymes to break up the protein component of hemoglobin into its peptide components. He showed that the patterns of the peptides from modern humans, gorilla and chimpanzee were indistinguishable. Goodman used a different method, immunodiffusion, to study albumin, a serum protein. He showed that the patterns produced by the albumins of modern humans and the chimpanzee were identical. He concluded that this was because the albumin molecules were, to all intents and purposes, identical.

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Change in gene expression between humans and apes:

 

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Specific examples of chromosomal differences between human and chimpanzee include:

  1. Humans have 23 pairs of chromosomes while chimpanzees have 24. Evolutionary scientists believe that one of the human chromosomes has been formed through the fusion of two small chromosomes in the chimp instead of an intrinsic difference resulting from a separate creation.
  2. At the end of each chromosome is a string of repeating DNA sequences called a telomere. Chimpanzees and other apes have about 23 kilobases (a kilobase is 1,000 base pairs of DNA) of repeats. Humans are unique among primates with much shorter telomeres only 10 kilobases long.
  3. While 18 pairs of chromosomes are ‘virtually identical’, chromosomes 4, 9 and 12 show evidence of being ‘remodelled.’ In other words, the genes and markers on these chromosomes are not in the same order in the human and chimpanzee. Instead of ‘being remodelled’ as the evolutionists suggest, these could, logically, also be intrinsic differences because of a separate creation.
  4. The Y chromosome in particular is of a different size and has many markers that do not line up between the human and chimpanzee.
  5. Scientists have prepared a human-chimpanzee comparative clone map of chromosome 21 in particular. They observed ‘large, non-random regions of difference between the two genomes.’ They found a number of regions that ‘might correspond to insertions that are specific to the human lineage.’

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Chimps, Humans 96 Percent the Same, Gene Study Finds in 2005:

Because chimpanzees are our closest living relatives, the chimp genome is the most useful key to understanding human biology and evolution, next to the human genome itself. The breakthrough will aid scientists in their mission to learn what sets us apart from other animals. By comparing human and chimpanzee genomes, the researchers have identified several sequences of genetic code that differ between human and chimp. These sequences may hold the most promise for determining what creates human-specific traits such as speech. The project was conducted by an international group of scientists called the Chimp Sequencing and Analysis Consortium. Sixty-seven researchers co-authored the study, which is detailed in the journal Nature.

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To map the chimp genome, researchers used DNA from the blood of a male common chimpanzee (Pan troglodytes) named Clint, who lived at the Yerkes National Primate Research Center in Atlanta. A comparison of Clint’s genetic blueprints with that of the human genome shows that our closest living relatives share 96 percent of our DNA. The number of genetic differences between humans and chimps is ten times smaller than that between mice and rats. Scientists also discovered that some classes of genes are changing unusually quickly in both humans and chimpanzees, as compared with other mammals. These classes include genes involved in the perception of sound, transmission of nerve signals, and the production of sperm.  Despite the similarities in human and chimp genomes, the scientists identified some 40 million differences among the three billion DNA molecules, or nucleotides, in each genome. The vast majority of those differences are not biologically significant, but researchers were able to identify a couple thousand differences that are potentially important to the evolution of the human lineage.

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Comparing the human and chimpanzee genomes: Searching for needles in a haystack a 2005 study:

The chimpanzee genome sequence is a long-awaited milestone, providing opportunities to explore primate evolution and genetic contributions to human physiology and disease. Humans and chimpanzees shared a common ancestor ∼5-7 million years ago (Mya). The difference between the two genomes is actually not ∼1%, but ∼4%—comprising ∼35 million single nucleotide differences and ∼90 Mb of insertions and deletions. The challenge is to identify the many evolutionarily, physiologically, and biomedically important differences scattered throughout these genomes while integrating these data with emerging knowledge about the corresponding “phenomes” and the relevant environmental influences.

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DNA comparison between human and chimpanzee:

  • Both human and chimp genomes are 2.9 Gb in size.
  • Diploid number of chromosomes in chimpanzee is 48 whereas in human is 46. Human chromosome 2 evolved from an end-to-end fusion of two ancestral chromosomes subsequent to the split of human and chimp lineages.
  • Mean divergence of all chromosomes is 1.23%.
  • Mean divergence of X chromosomes is 0.94%.
  • Mean divergence of Y chromosomes is 1.9%.
  • Mean divergence at fixed (nonpolymorphic) sites is 1.06% (the lower divergence at fixed sites in comparison of any two copies of the respective genomes is because sites polymorphic in each species contribute to estimated divergence of some 11 to 22%).
  • Mean divergence at CpG sites is 15.2% (CpG to TpG mutations occur at a rate 10-12-fold higher than for other nucleotides).
  • Number of nucleotide substitutions is 35 million.
  • Number of insertions and deletions is 5 million.
  • Total amount of sequence as insertion or deletion (indel) is 90 Mb.
  • Divergence including indels is 4.5% (insertions and deletions make a larger contribution to human-chimp divergence than nucleotide substitutions).
  • Lineage-specific number of new Alu insertions is 7,000 in human and ~2,300 in chimp (the three-fold higher activity of Alu elements in the human lineage is mainly due to activity of two new subfamilies (AluYa5 and AluYb8) that evolved since the human-chimp divergence).
  • Number of lineage-specific new L1 insertion is ~2,000 in both species.
  • Nucleotide sequence divergence between mitochondrial genomes is estimated to be 8.9% or higher.

The degree of nucleotide and especially protein sequence divergence between chimpanzee and human is apparently insufficient to account for all the differences between these two species. Thus, it has been proposed that regulatory changes leading to gene expression differences are likely to be responsible.

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Genetic evidence for complex speciation of humans and chimpanzees a 2006 study:

Humans (Homo sapiens) and chimpanzees (Pan troglodytes) last shared a common ancestor ∼5-7 million years ago (Mya) (Chen and Li 2001; Brunet et al. 2002). The genetic divergence time between two species varies substantially across the genome, conveying important information about the timing and process of speciation. Here authors develop a framework for studying this variation and apply it to about 20 million base pairs of aligned sequence from humans, chimpanzees, gorillas and more distantly related primates. Human chimpanzee genetic divergence varies from less than 84% to more than 147% of the average, a range of more than 4 million years. The analysis also shows that human chimpanzee speciation occurred less than 6.3 million years ago and probably more recently, conflicting with some interpretations of ancient fossils. Most strikingly, chromosome X shows an extremely young genetic divergence time, close to the genome minimum along nearly its entire length. These unexpected features would be explained if the human and chimpanzee lineages initially diverged, then later exchanged genes before separating permanently

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‘Junk DNA’ defines differences between humans and chimps a 2011 study:

For years, scientists believed the vast phenotypic differences between humans and chimpanzees would be easily explained — the two species must have significantly different genetic makeups. However, when their genomes were later sequenced, researchers were surprised to learn that the DNA sequences of human and chimpanzee genes are nearly identical. What then is responsible for the many morphological and behavioral differences between the two species? Researchers at the Georgia Institute of Technology have now determined that the insertion and deletion of large pieces of DNA near genes are highly variable between humans and chimpanzees and may account for major differences between the two species. The research team lead by Georgia Tech Professor of Biology John McDonald has verified that while the DNA sequence of genes between humans and chimpanzees is nearly identical, there are large genomic “gaps” in areas adjacent to genes that can affect the extent to which genes are “turned on” and “turned off.” The research shows that these genomic “gaps” between the two species are predominantly due to the insertion or deletion (INDEL) of viral-like sequences called retrotransposons that are known to comprise about half of the genomes of both species. “These genetic gaps have primarily been caused by the activity of retroviral-like transposable element sequences,” said McDonald. “Transposable elements were once considered ‘junk DNA’ with little or no function. Now it appears that they may be one of the major reasons why we are so different from chimpanzees. Our findings are generally consistent with the notion that the morphological and behavioral differences between humans and chimpanzees are predominately due to differences in the regulation of genes rather than to differences in the sequence of the genes themselves,” said McDonald.

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Chimps show much greater genetic diversity than humans:

The researchers found chimpanzees from different populations were substantially more different genetically than humans living on different continents. Groups of chimpanzees within central Africa are more different genetically than humans living on different continents, an Oxford University-led study has found.  Oxford University researchers, along with scientists from the University of Cambridge, the Broad Institute, the Centre Pasteur du Cameroun and the Biomedical Primate Research Centre, examined DNA from 54 chimpanzees. They compared the DNA at 818 positions across the genome that varied between individuals.  Their analysis showed that Cameroonian chimpanzees are distinct from the other, well-established groups. And previous conclusions that Cameroonian and western chimpanzees are most closely related were shown to be untrue. Instead, the closest relationships to Cameroonian chimpanzees are with nearby central chimpanzees. Dr Rory Bowden from the Department of Statistics at Oxford University, who led the study, said: ‘These findings have important consequences for conservation. All great ape populations face unparalleled challenges from habitat loss, hunting and emerging infections, and conservation strategies need to be based on sound understanding of the underlying population structure. The fact that all four recognized populations of chimpanzees are genetically distinct emphasizes the value of conserving them independently.’ The researchers also contrasted the levels of genetic variation between the chimpanzee groups with that seen in humans from different populations.  Surprisingly, even though all the chimpanzees live in relatively close proximity, chimpanzees from different populations were substantially more different genetically than humans living on different continents. That is despite the fact that the habitats of two of the groups are separated only by a river. Professor Peter Donnelly, director of the Wellcome Trust Centre for Human Genetics at Oxford University and a senior author on the study, noted: ‘Relatively small numbers of humans left Africa 50,000-100,000 years ago. All non-African populations descended from them, and are reasonably similar genetically.’ ‘That chimpanzees from habitats in the same country, separated only by a river, are more distinct than humans from different continents is really interesting. It speaks to the great genetic similarities between human populations, and to much more stability and less interbreeding over hundreds of thousands of years in the chimpanzee groups.’

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A missing Genetic Link in Human Evolution from common ancestor: core duplicons: a 2014 study:

About 8 million to 12 million years ago, the ancestor of great apes, including humans, underwent a dramatic genetic change. Small pieces of DNA replicated and spread across their resident chromosomes like dandelions across a lawn. But as these “dandelion seeds” dispersed, they carried some grass and daisy seeds — additional segments of DNA — along for the ride. This unusual pattern, repeated in different parts of the genome, is found only in great apes — bonobos, chimpanzees, gorillas and humans. “I think it’s a missing piece of human evolution,” said Evan Eichler, a geneticist at the University of Washington, in Seattle. “My feeling is that these duplication blocks have been the substrate for the birth of new genes.” Despite the duplication-linked genes’ potential importance in human evolution, most have not been extensively analyzed. The repetitive structure of the duplicated regions makes them particularly difficult to study using standard genetic approaches — the most efficient methods for sequencing DNA start by chopping up the genome, reading the sequence of the small chunks and then assembling those sections like one would a puzzle. Trying to assemble repetitive sections is like trying to put together a puzzle made of pieces with almost the same pattern. “Because these regions are so complex, they are often ignored by conventional genome studies, and some regions still haven’t been fully sequenced,” said James Sikela, a geneticist at the University of Colorado School of Medicine in Aurora. “So not only are they important, they are unfortunately unexamined.”

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A Genetic Burst:

In 2007, Eichler and his collaborators took on what seemed like a Herculean task — looking comprehensively at the repetitive stretches of the human genome. Previous studies had characterized individual regions, but Eichler’s team employed new computational techniques and comparative genomics — comparing DNA sequences from different species — to examine the entire genome. Mathematical analysis published in Nature Genetics that year revealed a set of “core duplicons” — stretches of DNA that appear over and over on a specific chromosome. The core duplicon anchors an architecturally complex stretch of DNA, acting as the focal point for a larger block of duplications. Although scientists aren’t sure how, the core seems to sweep up neighboring segments of DNA, duplicating the entire stretch and inserting the new copy into a new location on the chromosome. “Then it picks up again and duplicates some of the sequence around it and moves to another new location,” Eichler said. “It seems to be an extremely unstable genetic element that provides a template for evolutionary change.”

It is this process that appears to create new genes: When new duplications are inserted into the genome, they bring together two previously foreign pieces of DNA, which can lead to new functional components, such as proteins. This chaotic mix-and-match approach is different from the traditional model for the creation of a gene, in which an existing gene is duplicated and the copy is free to develop new functions. “This mechanism appears to be seminal in our evolution,” said Philip Hastings, a geneticist at Baylor College of Medicine, in Houston. “It’s possible that we are the way we are largely because of this mechanism that generates dramatic episodes of chromosomal structural change.” The pattern that the duplicons create seems to be unique to great apes, suggesting the mechanism itself is also unique to these species. In other animals, duplicated regions are lined up next to one another rather than dispersed along the chromosome. The duplicated regions in great apes tend to be very active, meaning that their genes are turned on more often than genes in other areas and that they are producing more RNAs and proteins. That suggests these regions are functionally important.

Eichler and others have so far characterized the structure of only about half of the roughly dozen duplicon regions, each of which is unique to their resident chromosome. Most of the analysis to date has focused on the region’s evolutionary history, including where the genes came from, how quickly they are evolving and how they are related to one another. Eichler said his team has had a more difficult time understanding what they do, although he and others have managed to study the function of a handful of the duplication-linked genes.

What the scientists do know is that the genes appear to be important in evolution. According to Eichler, about a third of the gene families linked to core duplicons show signs of positive selection — meaning that they boost survival of their bearers and are passed on to the next generation, contributing to evolution — compared to about 5 percent of genes overall. Indeed, a gene on one of the cores, first described more than 10 years ago, appears to be the fastest-evolving human gene. However, Eichler cautioned, it’s tricky to measure positive selection in these human or ape-specific genes because scientists have little to compare them to. To measure selection, scientists typically compare a gene in different species to examine how much it has changed.

Much like the rings of a tree trunk, the outer regions of core duplicons are the newest, arising from the latest round of replications. These regions also tend to be the most variable from person to person. They may therefore contribute to disease — extra or deleted copies of important genes or DNA segments are likely to affect how well cells or organs function. Eichler’s team aims to use the new approaches to track variation in duplicated regions, which could give insight into what these genes do. The researchers will look for variations in 30 human-specific genes within these zones in children with developmental disorders such as intellectual disability and epilepsy. If changes in a certain gene or region are reliably linked to specific traits, like a change in brain size, it gives hints to the gene’s function. Duplication-linked genes studied to date “seem to be important for cell proliferation, either speeding it up or slowing it down,” Eichler said. “They are expressed in many tissues but highly in the brain, often in neurons, and often in areas of rapid cell division.” In fact, some of the genes have been linked to cancer when they become overactive.

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Bigger Brains:

About 3.4 million years ago, a core duplicon on what is now called chromosome 1 in human descendants made one of its characteristic jumps, taking with it a copy of a gene known as SRGAP2. A million or so years later, it jumped again, creating a granddaughter of the original. No other mammals whose genomes have been examined to date have multiple copies of the gene, and the jumps coincide with a pivotal point in human evolution: As Australopithecus evolved into Homo habilis 2 to 3 million years ago, hominid brains were on their way to doubling in size. The granddaughter gene, known as SRGAP2C, may be particularly important for the human brain. In 2012, Eichler’s team and a group from the Scripps Research Institute near San Diego showed that SRGAP2C can influence how neurons migrate in a developing brain. By expressing the human version of the gene in mice, the Scripps team showed that SRGAP2C slows the maturation of certain brain cells and triggers the development of a denser array of neuronal structures called spines, which help form connections between brain cells. “I’m not saying it’s responsible for the expansion of the human brain, but it might play a role in getting neural precursors [cells that give birth to neurons] to the right place,” Eichler said. The SRGAP2 findings show how a human-specific genetic change led to changes in neurons. “That’s what has been missing from the field,” said Genevieve Konopka, a neuroscientist at the University of Texas Southwestern Medical Center, in Dallas. “People have identified unique changes in the human lineage, but they haven’t really followed up on them in any functional manner.” Konopka said studies such as the SRGAP2 paper, which delve into the function of a gene, can help to clarify the role that human-specific genetic changes play in our development as a species. “Anytime you can show something is unique in the human genome and how it modifies the biology, that is a unique and important thing to do,” she said.

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While evidence that core duplicons are a driving force behind human evolution is growing, many questions remain. For example, it’s unclear what triggered the creation of these cores or how they spread. One popular theory points to a class of viruses known as retroviruses, which can insert DNA into their host’s genome that is then passed from generation to generation. Perhaps a retrovirus was responsible for the initial core duplicons. A significant portion of our genome is known to arise from viruses that have left the imprint of their DNA but are no longer active in our cells. “My favorite hypothesis is that at a key point in great ape evolution, there was a burst in retroviral activity,” said Edward Hollox, a geneticist at the University of Leicester, in Great Britain. Intriguingly, the core duplicons once so active in our genomes seem to have slowed or stopped hopping. Despite evidence for several spurts in the great ape evolutionary history, scientists have yet to find duplications that occurred in the past few million years. Eichler’s team has searched for such cases, finding some younger duplications that the scientists think are specific to humans and distinct from Neanderthals. “But they are the exception rather than the rule,” he said. It’s not yet clear how big a role core duplicons played in the formation of our species. “It’s very difficult to provide an overarching theory of great ape evolution,” Hollox said. “Undoubtedly, the core duplicon hypothesis is part of it. To what extent it contributes, the jury is still out.” Research suggests other factors such as gene regulation — when and where specific genes are turned on — play a part as well. But changes in gene regulation are probably not sufficient to explain all the differences between primates and humans. “I know there are going to be multiple paths to brain evolution,” Konopka said, adding that core duplicons are “probably one of the main players.”

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Molecular Phylogeny of the Hominoids: a 2018 study:

Consensus on the evolutionary relationships of humans, chimpanzees, and gorillas has not been reached, despite the existence of a number of DNA sequence data sets relating to the phylogeny, partly because not all gene trees from these data sets agree. However, given the well-known phenomenon of gene tree-species tree mismatch, agreement among gene trees is not expected. A majority of gene trees from available DNA sequence data support one hypothesis, but is this evidence sufficient for statistical confidence in the majority hypothesis?

All available DNA sequence data sets showing phylogenetic resolution among the hominoids are grouped according to genetic linkage of their corresponding genes to form independent data sets. Of the 14 independent data sets defined in this way, 11 support a human-chimpanzee clade, 2 support a chimpanzee-gorilla clade, and one supports a human-gorilla clade. The hypothesis of a trichotomous speciation event leading to Homo, Pun, and Gorilla can be firmly rejected on the basis of this data set distribution. The multiple-locus test (Wu 1991), which evaluates hypotheses using gene tree-species tree mismatch probabilities in a likelihood ratio test, favors the phylogeny with a Homo-Pun clade and rejects the other alternatives with a P value of 0.002. When the probabilities are modified to reflect effective population size differences among different types of genetic loci, the observed data set distribution is even more likely under the Homo-Pun clade hypothesis. Maximum-likelihood estimates for the time between successive hominoid divergences are in the range of 300,000 to 2800,000 years, based on a reasonable range of estimates for long-term hominoid effective population size and for generation time. The implication of the multiple-locus test is that existing DNA sequence data sets provide overwhelming and sufficient support for a human-chimpanzee clade: no additional DNA data sets need to be generated for the purpose of estimating hominoid phylogeny. Because DNA hybridization evidence (Caccone and Powell 1989) also supports a Homo-Pun clade, the problem of hominoid phylogeny can be confidently considered solved.

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Why aren’t apes evolving into humans?

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Are apes monkeys?

We are using the term monkey colloquially, and include chimpanzees and gorillas under the general umbrella of monkeys. Technically those are apes, but they are non-human primates that are indeed descended from monkeys. Apes do not have tails, while most monkey species do. Apes tend to be larger than monkeys and usually have larger brains. … Ape species include humans, gorillas, chimpanzees, orangutans, gibbons, and bonobos. Humans belong to family of great apes (hominids). The last common ancestor of monkeys and great apes lived about 25 million years ago. In evolutionary and genetic terms, ape species are much closer to humans than monkeys are. Monkeys are much more like other mammals than apes and humans are.

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First of all, the creatures we call apes are our cousins, not our ancestors; which would make it very hard for them to evolve into something like us. Humans did not evolve from apes, gorillas or chimps. We are all modern species that have followed different evolutionary paths, though humans share a common ancestor with some primates, such as the African ape. The timeline of human evolution is long and controversial, with significant gaps. Experts do not agree on many of the start and end points of various species. So this chart involves significant estimates.

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It’s easy to think about evolution as a linear, progressive drive toward greater and greater complexity, something that started with single-celled amoebas and ended with us. But evolution doesn’t have a destination, and even if it did, humans are certainly not it. In many cases, evolution tends to favor simplicity. That’s why creatures that live in caves lose their eyes, and whales — which are descended from terrestrial mammals — have almost no leg bones. Not even intelligence is sacred: sea urchins, which have no central nervous system, evolved from an ancestor with a brain. “Evolution is about survival under particular conditions, and random mutations,” says Nina Jablonski, a paleoanthropologist at Penn State. “There’s a big element of chance and certainly no element of direction. … Living things are just trying to adapt to the contingencies of life in their environment.”

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The diversity of hominins during the earliest stages of human evolution showed how several species tried to do that. For example, it’s thought that Australopithecus afarensis (Lucy’s species) evolved human-like hips that let them walk on two feet because it let them carry things — a useful skill for collecting food on the savanna. Paranthropus robustus had a powerful jaw for chewing the tough, fibrous foods available in their dry environment. Homo habilis had a relatively huge brain that helped them make early stone tools. Australopithecus boisei’s massive molars let him dine on mostly nuts and seeds. But as hominins’ tool use got more sophisticated, their ecological niches expanded. Species didn’t have to choose between having big molars for chewing seeds and sharp canines for ripping meat — with tools, they could partially break the food before eating it and consume both. As the technological complexity of humans increases … one species with tools is able to do more than two or three species could in the past. Homo species with larger brains and smaller teeth were more ecologically successful, so evolution favored those groups. The development of language added to our ancestors’ evolutionary toolkit, helping them hunt, travel, anticipate and avoid threats. By the time Homo sapiens arose roughly 200,000 years ago, they were able to survive in almost any environment, under any circumstances. In other words, modern humans were able to outlive other hominins because we were equipped to exploit multiple ecological niches under the particular circumstances in which we lived.

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That’s important to remember when we ask why our ape cousins aren’t evolving the traits that characterize humans. Modern great apes live in heavily forested environments where the ability to climb trees is a big bonus — so they have no need for human bipedalism. Creatures like chimpanzees and bonobos are capable of building nests, using rudimentary tools, appreciating beauty, and perhaps even mourning their dead — without our energy-guzzling big brains. When we look at our ape relatives today, they’re just fine being apes. They’re doing their chimp stuff, their orangutan stuff, their gorilla stuff; they don’t need to be more human-like because they’re surviving perfectly.

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To say we are more “evolved” than our hairy cousins is just wrong. Thinking that a species evolves in order to survive is to put the cart before the horse. Genetic mutations happen all the time, without fanfare and often without any measurable change in the organism’s lifestyle. In general, the mutations most likely to be passed to future generations are those that prove useful to either individual or species survival. The “usefulness” of a mutation depends largely on shifting environmental factors like those of food, predators, and climate, and also on social pressures. Evolution is a matter of filling ecological and social niches. African apes are still around because their environment has encouraged the reproductive success of individuals with different genetic material than ours.

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It is natural to think of humans as “more evolved” than other animals, but this isn’t true in any scientific sense. We are differently evolved, simply adapted to a different environment. It so happens that our intelligence, and the culture and technology that it spawned has turned out to allow us an unprecedented degree of success, and the ability to live in environments that our ancestors couldn’t. But evolution didn’t somehow anticipate this. The point is, evolution is only “directed” in that it favors survival, it does not favor high intelligence or walking upright or use of tools, unless those features aid in the survival and passing on of genes to the next generation. Other animals, for instance mosquitos, don’t seem to be suffering for lack of these human-like capabilities.  Evolution is an ongoing process of trial and error, of which all modern primates are still a part.

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Moral of the story:

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  1. Evolution, a theory in biology postulates that the various types of plants, animals, and other living things on Earth have their origin in other pre-existing types and that the distinguishable differences are due to modifications in successive generations. Biological evolution is a process of descent with modification. Lineages of organisms change through generations; diversity arises because the lineages that descend from common ancestors diverge through time. Evolutionary processes give rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules.

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  1. Darwin contributed to the modern understanding of biological evolution by thoroughly documenting the variation of living forms and by identifying the process of natural selection. But Darwin did not understand how individuals pass on traits to their offspring. Mendel’s Laws of Inheritance helped revive Darwin’s theory. Neither Darwin nor Mendel knew anything about DNA. We now know Mendel’s particles or units of inheritance as genes. Combining Darwin’s theory of evolution with Mendel’s genetics was the most important breakthrough in biology known as synthetic theory of evolution. According to synthetic theory, evolution is the change of genes in a given population over a number of generations. Evolutionary change is based on changes in the genetic makeup of populations over time. Populations, not individual organisms, evolve. Evolution occurs slowly and gradually, but it can also occur rapidly.

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  1. Without differences in fitness natural selection cannot act and adaptation cannot occur. Given its central role in evolutionary biology, one might expect the idea of fitness to be both straightforward and widely understood but this may not be the case. In evolutionary terms, fitness has a very different meaning than the everyday meaning of the word. The fittest organisms in a population are not those that are strongest, healthiest, fastest, and/or largest. Fitness means organism’s ability to get its genes into the next generation. Fitness involves the ability of organisms to survive and reproduce in the environment in which they find themselves. The consequence of this survival and reproduction is that organisms contribute genes to the next generation.

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  1. Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction; whereas microevolution refers to smaller evolutionary changes within a species or population, in particular shifts in gene frequency and adaptation. Convergent evolution occurs in different species that have evolved similar traits independently of each other due to natural selection. Traits arising through convergent evolution are analogous structures, in contrast to homologous structures, which have a common origin, but not necessarily similar function. The opposite of convergent evolution is divergent evolution, whereby related species evolve different traits due to random mutation unrelated to adaptive changes.

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  1. The processes by which genetic changes occur, from one generation to another, are called evolutionary processes or mechanisms. The four most widely recognised evolutionary processes are natural selection (including sexual selection), genetic drift, mutation and gene migration (gene flow). It is important to keep in mind that these processes may act concurrently.

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  1. Gene migration, or gene flow, is defined in an evolutionary sense as “the transfer of alleles from the gene pool of one population to the gene pool of another population” caused by the movement of individuals between separate populations of organisms.

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  1. Genetic drift is the change in allele frequency from one generation to the next that occurs because alleles are subject to sampling error. Genetic drift occurs not because it improves survival, but just because of chance. Even in the absence of selective forces, genetic drift can cause two separate populations that began with the same genetic structure to drift apart into two divergent populations with different sets of alleles. Natural selection is adaptive force while genetic drift is non-adaptive force driving evolution. Natural selection usually predominates in large populations whereas genetic drift does so in small ones.

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  1. Natural selection will only cause evolution if there is enough genetic variation in a population. Genetic Variation comes from mutations in the genome, reshuffling of genes through sexual reproduction and migration between populations (gene flow). Genetic variation is simply the variation in alleles of genes in the gene pool of a species or a population. Allele frequency is an accurate measurement of the amount of genetic variation in a population. Genetic variation lays the foundation for organisms to have genetic diversity which is the total number of genetic characteristics in the genetic makeup of a species. The modern evolutionary synthesis theory defines evolution as the change over time in this genetic variation.

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  1. Mutation can be defined as a change in the DNA sequence within a gene or chromosome of a living organism. When a cell divides in two, it makes a copy of its genome, and then parcels out one copy to each of the two new cells. Theoretically, the entire genome sequence is copied exactly, but in practice a wrong base is incorporated into the DNA sequence every once in a while, or a base or two might be left out or added. These mistakes—”changes” might be a more accurate word, because they are not always bad news—are called mutations. Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage. When a mutation occurs in a sex cell—a sperm or an egg—it can be passed along to the next generation of people. Most times, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism. If so, it will become more prevalent in the next generation and spread throughout the population. In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. The average human newborn has 60 new mutations and up to 10% of new mutations are expected to be deleterious. Mutations are random, but selection for them is not random. Although mutations are random and a major source of variation, mutation may also function as a mechanism of evolution when there are different probabilities at the molecular level for different mutations to occur, a process known as mutation bias.

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  1. Natural selection is the process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent in the population over time. Natural selection simply selects traits that enable individuals to survive and reproduce, yielding more copies of those individuals’ genes in the next generation. In natural selection, those variations in the genotype that increase an organism’s chances of survival and procreation are preserved and multiplied from generation to generation at the expense of less advantageous ones. Evolution often occurs as a consequence of this process. Natural selection may arise from differences in survival, in fertility, in rate of development, in mating success, or in any other aspect of the life cycle. All such differences result in natural selection to the extent that they affect the number of progeny an organism leaves. Natural selection can change a species in small ways, causing a population to change color or size over the course of several generations. This is called “microevolution.” Microevolution is the change in allele frequencies that occurs over time within a population. But natural selection is also capable of much more. Given enough time and enough accumulated changes, natural selection can create entirely new species, known as “macroevolution.” It can turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into humans. Natural selection can act at different levels of organisation, such as genes, cells, individual organisms, groups of organisms and species.

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  1. Natural selection is not survival of the fittest but survival of the fit enough. Natural selection preserves the gains and eradicates the mistakes. Natural selection is a “self-evident” mechanism and not voluntary or wilful mechanism. Natural selection has no foresight and no intentions (artificial selection is intentional). Natural selection cannot select a trait that is unavailable in genetic variation. If a population or species doesn’t happen to have the right kinds of genetic variation, it will not evolve in response to the environmental changes and may become extinct. Natural selection does not automatically provide organisms with the traits they “need” to survive. Natural selection makes nature i.e. ecosystem the measure against which individuals and individual traits, are more or less likely to survive. Natural selection results in adaptations — features of organisms that appear to suit the environment in which the organisms live. While some traits are adaptive, it’s important to keep in mind that many traits are not adaptations at all. Even without selecting any new trait or deleting any existing trait, organism can survive and reproduce albeit without evolution. Life without evolution is status co i.e. no change in genome. Here allele frequency (variations in a gene) will remain constant due to absence of selection, mutation, migration and genetic drift.

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  1. Adaptations are produced by natural selection. Adaptation is the process that makes organisms better suited to their habitat by gain of a new feature, or the loss of an ancestral feature. Adaptation occurs through the gradual modification of existing structures. Adaptations can only occur if they are evolvable. DNA cannot be totally prevented from undergoing somatic replication corruption; this has meant that cancer, which is caused by somatic mutations, cannot be completely eliminated by natural selection.

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  1. Natural selection does result in the evolution of improved abilities to survive and reproduce; however, this does not mean that evolution is progressive. First, natural selection does not produce organisms perfectly suited to their environments. It often allows the survival of individuals with a range of traits — individuals that are “good enough” to survive. Hence, evolutionary change is not always necessary for species to persist. Many taxa (like some mosses, fungi, sharks, opossums, and crayfish) have changed little physically over great expanses of time. Second, there are other mechanisms of evolution that don’t cause adaptive change. Mutation, gene migration, and genetic drift may cause populations to evolve in ways that are actually harmful overall or make them less suitable for their environments. Finally, the whole idea of “progress” doesn’t make sense when it comes to evolution as an organism with traits that are beneficial in one situation may be poorly equipped for survival when the environment changes. A common misconception is that evolution has goals, long-term plans, or an innate tendency for “progress”; however, evolution has no long-term goal and does not necessarily produce greater complexity. Although complex species have evolved, they occur as a side effect of the overall number of organisms increasing and simple forms of life still remain more common in the biosphere.

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  1. Formation of new species is called speciation. Extinction is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation and disappear through extinction. More than 99 percent of all species, amounting to over five billion species that ever lived on Earth are estimated to be extinct, and extinction appears to be the ultimate fate of all species. Humans may have come close to extinction about 70,000 years ago and at one point there may have been only 2,000 individuals alive as our species teetered on the brink. The small genetic diversity of modern humans indicates that at some stage, the human population dwindled to a very low level. It was out of this small population, with its consequent limited genetic diversity, that today’s humans descended.

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  1. Inherited traits are controlled by genes and the complete set of genes within an organism’s genome is called its genotype. The complete set of observable traits that make up the structure and behaviour of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment. A substantial part of the phenotypic variation in a population is caused by genotypic variation. Even relatively small differences in genotype can lead to dramatic differences in phenotype: for example, chimpanzees and humans differ in only about 4% of their genomes.

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  1. All great apes, including baboons, gibbons, orangutans, gorillas, chimpanzees, humans, and human ancestors, belong in the superfamily Hominoidea. Of these great apes, all but baboons and gibbons belong in the family Hominidae. Gorillas, chimpanzees, humans, and human ancestors belong in the subfamily Homininae. Humans and their direct ancestors belong in the tribe Hominini. A human is a member of the genus Homo, of which Homo sapiens is the only extant species, and within that Homo sapiens sapiens is the only surviving subspecies. Homo sapiens means ‘the thinking man’ or ‘the wise man’. During a time of dramatic climate change 200,000 years ago, Homo sapiens evolved in Africa. Extinct species of the genus Homo are classified as “archaic humans”. While some (extinct) Homo species might have been ancestors of Homo sapiens, many, perhaps most, were likely “cousins”, having speciated away from the ancestral hominin line. There is yet no consensus as to which of these groups should be considered a separate species and which should be a subspecies. Homo sapiens are known as modern humans or anatomically modern humans i.e. our own species who lived during prehistoric times. Homo sapiens sapiens are humans living on earth for last 10,000 years. All of us are Homo sapiens sapiens.

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  1. Although humans didn’t descend from apes; humans and apes, both living and extinct, are related, is accepted by anthropologists and biologists everywhere. Human Chromosome 2 is a fusion of two ancestral chromosomes. All great apes apart from man have 24 pairs of chromosomes. Therefore the common ancestor of all great apes had 24 pairs of chromosomes and that the fusion of two of the ancestor’s chromosomes created chromosome 2 in humans. Evidence from the fossil record and comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common ancestor approximately 7 million years ago. The timeline of human evolution spans approximately 7 million years, from the separation of the Pan genus (chimpanzee) until the emergence of behavioral modernity by 50,000 years ago. The first 3 million years of this timeline concern Sahelanthropus, the following 2 million concern Australopithecus and the final 2 million span the history of the Homo genus in the Paleolithic era. Human evolution from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental, physiological, and behavioral changes. The most significant of these adaptations are bipedalism, increased brain size, shorter jaws with smaller teeth, use of tools, lengthened ontogeny (gestation and infancy), and decreased sexual dimorphism. Fossil evidence shows that our ancestors became bipeds first, followed by changes to the teeth and jaws. It was only much later that our larger brains and more complex technology set us apart as Homo sapiens.

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  1. About seven million years ago, our early ancestors climbed trees and walked on four legs when on the ground. By five million years ago, our ancestors had developed the ability to walk on two legs but their gait was quite different from our own and their skeletons retained some features that helped them climb trees. By 1.8 million years ago, our ancestors had developed long legs and an efficient striding gait that made it easier to travel longer distances. There are several theories of the adaptation value of bipedalism. It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion, enabled long distance running and hunting, provided an enhanced field of vision, and helped avoid hyperthermia by reducing the surface area exposed to direct sun; features all advantageous for thriving in the new savanna and woodland environment created as a result of climate change.

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  1. Anthropological evidence from cranio-dental features and fossil stable isotope analysis indicates a growing reliance on meat consumption during human evolution. Our early ancestors had diets that consisted mainly of low-nutrient plant material. This meant that they needed to spend significant amounts of time feeding in order to consume their energy requirements. The inclusion of meat in the diet was a turning point in human evolution. Eating meat provided our ancestors with more proteins and fats and higher energy levels. This allowed them to develop and sustain an active lifestyle and develop a larger brain.

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  1. It should be noted that many species make and use tools, but it is the human genus that dominates the areas of making and using more complex tools. The use of tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution, especially the continued expansion of the human brain. Increased tool use would allow hunting for energy-rich meat products, and would enable processing more energy-rich plant products. Improved technology and a greater reliance on meat in the diet may have affected tooth size since foods now needed to be chewed less. This is reflected in the reduced size of the premolars and molars – the teeth responsible for grinding food.

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  1. Many traits of human intelligence, such as empathy, theory of mind, mourning, ritual, and the use of symbols and tools, are apparent in great apes although in less sophisticated forms than found in humans, such as great ape language. It is clear that humans have become smarter during the evolution from their ape-like hominid ancestors, which lived seven million years ago, to Neanderthals. The brain of a modern human consumes about 20 watts (411 kilocalories per day), a fifth of the body’s resting power consumption. As brain is metabolically costly, encephalization i.e. evolutionary increase in brain size should be associated with significant advantages. The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language.

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  1. Fire control was one of the most important cultural conquests in human evolution. The oldest evidence of this control goes back 400,000 years. Fire provided a source of warmth, protection, improvement on hunting and a method for cooking food. Mastery of fire represented a true revolution in primitive communities. The first hominids to master fire were, in all certainty, Homo heidelbergensis, in Europe and possibly Homo erectus in Asia.

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  1. Homo erectus and Homo ergaster were the first to use fire and complex tools, and were the first of the hominin line to leave Africa, spreading throughout Africa, Asia, and Europe between 1.3 to 1.8 million years ago. Homo erectus lived between 1.8 million and 300,000 years ago and only his head and face differed from modern man. Toward the end, his brain was that of the size of modern man, and definitely could speak. Erectus developed tools, weapons, and fire; developed clothing for northern climates and learned to cook his own food. Most anthropologists believe that modern humans and Neanderthals are descendants of either Homo erectus or Homo ergaster.

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  1. There are two main scientific theories about the biological development and migration patterns of modern humans: Single Origin (Out of Africa, Population Replacement) and Multiregional (regional continuity model). The two main hypotheses agree that Homo erectus evolved in Africa and spread to the rest of the world around 1 – 2 million years ago; it is regarding our more recent history where they disagree. Out of Africa model suggests that modern humans evolved in Africa and migrated out of Africa to replace archaic humans in the rest of the world. Multiregional model suggests that modern humans evolved from archaic humans concurrently in different parts of world as there are similarities between some skull features found in modern humans and in archaic humans from the same regions.

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  1. Neanderthals are our closest extinct human relative who lived about 400,000 – 30,000 years ago. Neanderthals made and used a diverse set of sophisticated tools, controlled fire, lived in shelters, made and wore clothing, were skilled hunters of large animals and also ate plant foods, and occasionally made symbolic or ornamental objects. There is evidence that Neanderthals deliberately buried their dead and occasionally even marked their graves with offerings, such as flowers. No other primates, and no earlier human species, had ever practiced this sophisticated and symbolic behavior. Neanderthals, the closest evolutionary relatives of present-day humans, lived in large parts of Europe and western Asia before disappearing 30,000 years ago. Neanderthals shared 99.7 per cent of their DNA with modern humans i.e. 99.7% of the nucleotide sequences of the modern human and Neanderthal genomes are identical. [On average, in DNA sequence, each modern human is 99.9% similar to any other modern human] The out-of-Africa hypothesis suggests Neanderthals were a separate species (H. neanderthalensis) replaced as modern humans (H. sapiens) spread from Africa. The regional continuity hypothesis suggests Neanderthals were a subspecies (H. sapiens neanderthalensis) that evolved into modern humans (H. sapiens sapiens).

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  1. The Earth’s climate is not stable and fluctuates between colder periods called Ice Ages, and warmer periods known as Interglacials. Some of the most important milestones in human evolution (bipedalism, tool making, meat eating, brain enlargement etc.) correlated with times of greatest climate variability as a part of adaptation to new environment. As climate altered vegetation habitats (determined by rainfall, evapotranspiration, soils, and other aspects of the earth system), this habitat modification applied selective pressures on the fauna that used these habitats, leading to new adaptations, migration, speciation, or extinction. Besides climate and habitat changes, viruses also drive human evolution.

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  1. Variability selection is a process where genes that enable flexible interactions with the environment are favored. Natural selection is not always a matter of ‘survival of the fittest’ but also survival of those most adaptable to changing surroundings. Variability selection suggests that evolution, when faced with rapid climatic fluctuation, respond to the range of habitats encountered rather than to each individual habitat in turn.

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  1. Our skin color is determined by climate induced selection pressure. For those who live in tropical and subtropical regions, the risk of burns, blistering, and the likelihood of death from skin cancer induced by ultraviolet light is dramatically reduced by having dark skin. In Europe there is less sun and a lower risk of skin cancer, but there is the ever-present risk of rickets, so populations living in Europe became lighter-skinned over time because pale skin absorbs more sunlight, which is required to produce enough vitamin D. So there are at least two evolutionary selection forces working in concert, tending to grade skin colour according to latitude. Consequently racism based on skin color has no biological basis.

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  1. The primary resource for detailing the path of human evolution will always be fossil specimens. Fossils are important because they give direct evidence of the type of animals and plants that existed at a certain geological age. The nature of specific fossil specimens and species can be accurately described, as can the location where they were found and the period of time when they lived. Fossils provide solid evidence that organisms from the past are not the same as those found today. Though the fossil record does not include every plant and animal that ever lived, it provides substantial evidence for the common descent of life via evolution. The fossil record provides consistent evidence of systematic change through time—of descent with modification. From this huge body of evidence, it can be predicted that no reversals will be found in future paleontological studies. That is, amphibians will not appear before fishes, nor mammals before reptiles, and no complex life will occur in the geological record before the oldest eukaryotic cells. This prediction has been upheld by the evidence that has accumulated until now: no reversals have been found.

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  1. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. Thousands of human fossils enable researchers and students to study the changes that occurred in brain and body size, locomotion, diet, and other aspects regarding the way of life of early human species over the past 6 million years. Millions of stone tools, figurines and paintings, footprints, and other traces of human behavior in the prehistoric record tell about where and how early humans lived and when certain technological innovations were invented. The geographic distribution of plants and animals offers another commonly cited evidence for evolution.

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  1. The age of the fossil must be determined so it can be compared to other fossil species from the same time period. Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms. Various dating methods are available including stratigraphy, radiometric dating [Potassium-argon dating, Argon-argon dating, Carbon-14 dating, Uranium series and Fission track], thermoluminescence, optical stimulating luminescence, electron spin resonance, paleomagnetism and molecular clock.

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  1. Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating. DNA dating by comparing DNA sequences to ascertain amount of genetic difference between living organisms provides a complementary approach for dating evolutionary events which not only reconstruct relationships between different populations or species but also infer evolutionary history over deep timescales. Genetic changes from mutation and recombination provide two distinct clocks, each suited for dating different evolutionary events and timescales. In humans, about 36 recombination events occur per generation, one or two per chromosome; and about 60 nucleotide changes (mutation) per generation – minuscule in a genome made up of 6 billion base pairs. In human populations, the generation time typically ranges from 22 to 33 years. Because mutations accumulate so slowly, this clock works better for very ancient events, like evolutionary splits between species. The recombination clock, on the other hand, ticks at a rate appropriate for dates within the last 100,000 years.

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  1. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa. So Africa is the cradle of human beings.

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  1. Tools provide evidence for human evolution. Primitive tools (flint hand axes) have been found in remains from the Palaeolithic Age (10,000 to 2.5 million years ago). More advanced tools (arrowheads) have been found from the Mesolithic Age (6,000 to 10,000 years ago), and even more advanced tools have been found from the Neolithic Age (4,000 to 6,000 years ago).

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  1. Analysis of prehistoric stone artifacts reveals a preferential, clockwise rotation of stone cores during flaking. Experimental studies of early stone artifact manufacture show that this non-random pattern is consistent with that produced by right-handed toolmakers. This suggests that there was a genetic basis for right-handedness by 1.4 to 1.9 million years ago.

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  1. Vestigial structure is a genetically determined structures or attributes that have lost most or all of their ancestral function in a given species. The vestigial versions of a structure can be compared to the original version of the structure in other species in order to determine the homology of the structure. Therefore, vestigial structures can be considered evidence for evolution. Examples of vestigial structures in humans include wisdom teeth, the coccyx, the vermiform appendix, and other behavioural vestiges such as goose bumps and primitive reflexes. Cholesterol is not a vestigial molecule in humans but the way it is targeted by statins makes cholesterol vestigial molecule as doctors hypothesize that very low cholesterol due to statin has no harm. I humbly disagree.

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  1. Organisms from bacteria to humans to dinosaurs all have the same DNA system as a genetic code. This may point to evidence that all life evolved from a single common ancestor. The differences in such DNA sequences between two organisms should roughly resemble both the biological difference between them according to their anatomy and the time that had passed since these two organisms have separated in the course of evolution. The theory of common descent is supported by genetic similarities. For example, every living cell makes use of nucleic acids as its genetic material, and uses the same twenty amino acids as the building blocks for proteins. All organisms use the same genetic code (with some extremely rare and minor deviations) to specify the nucleic acid sequences that form proteins. The fact that the genetic code is universal to all living things suggests that we once had a common ancestor. Moreover, proteins in all organisms are invariably composed of the same set of 20 amino acids. This unity of composition and function is a powerful argument in favor of the common descent of the most diverse organisms. The proteomic evidence also supports the universal ancestry of life. Vital proteins, such as the ribosome, DNA polymerase, and RNA polymerase, are found in everything from the most primitive bacteria to the most complex mammals. The core part of the protein is conserved across all lineages of life, serving similar functions. Other overarching similarities between all lineages of extant organisms, such as DNA, RNA, amino acids, and the lipid bilayer, give support to the theory of common descent. The chirality of DNA, RNA, and amino acids is conserved across all known life. As there is no functional advantage to right- or left-handed molecular chirality, the simplest hypothesis is that the choice was made randomly by early organisms and passed on to all extant life through common descent.

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  1. Comparison of the DNA sequences of organisms reveals that phylogenetically close organisms have a higher degree of sequence similarity than organisms that are phylogenetically distant. Comparison of the DNA sequences allows organisms to be grouped by sequence similarity, and the resulting phylogenetic trees are typically congruent with traditional taxonomy, and are often used to strengthen or correct taxonomic classifications. The more closely two DNA sequences match, the more recently they would have shared a common ancestor. By analysing the DNA from different species scientists can start to generate family trees called phylogenetic trees. Genetic studies help researchers identify phylogeny, demographic history, dispersal patterns, and areas of the human genome influenced by natural selection.

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  1. The unifying principle of common descent that emerges from all the genetic and fossil evidence is being reinforced by the discoveries of modern biochemistry and molecular biology. For example, the protein cytochrome c, which is needed for aerobic respiration, is universally shared in aerobic organisms, suggesting a common ancestor that used this protein. There are also variations in the amino acid sequence of cytochrome c, with the more similar molecules found in organisms that appear more related (monkeys and cattle) than between those that seem less related (monkeys and fish). The cytochrome c of chimpanzees is the same as that of humans. The evidence for evolution from molecular biology is overwhelming and is growing quickly. In some cases, this molecular evidence makes it possible to go beyond the paleontological evidence. For example, it has long been postulated that whales descended from land mammals that had returned to the sea. Recent comparisons of some milk protein genes (beta-casein and kappa-casein) have confirmed this relationship and have suggested that the closest land-bound living relative of whales may be the hippopotamus. In this case, molecular biology has augmented the fossil record.

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  1. DNA dating (molecular clock) estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at a constant rate i.e. about three mutations per year in humans. Since genetic material (like DNA) decays rapidly, the molecular clock method can’t date very old fossils. The molecular clock varies significantly by species, sex, age and mutation type. It’s now clear that one mutation rate cannot determine the dates for all divergences relevant to human evolution. The molecular clock cannot assign concrete dates and must be calibrated against independent evidence, such as the fossil records which are dated by radiometric dating and other dating methods.

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  1. Besides DNA sequence comparison and DNA dating, other methods of DNA evidence for evolution comes from Endogenous retroviruses (ERV), pseudogenes, microsatellites, genetic synonyms, genetic scars and chromosome 2 of human which is fusion of two separate ancestral chromosomes.

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  1. Our mitochondrial DNA is essentially identical to that of our mother. Mitochondrial DNA is transferred from mother to daughter, generation after generation. The mitochondrial DNA in the son, which he got from his mother, is a dead end street, since his mitochondrial DNA will not be used in his children. Several unique properties of human mitochondrial DNA (mtDNA), including its high copy number, maternal inheritance, lack of recombination, and high mutation rate, have made it the molecule of choice for studies of human population history and evolution. Once the fertilization process gets over, the coding region of mitochondrial DNA mutates at the rate of about 0.017×10-6/site/year. The hypervariable region is the one with no coding where the rate of mutation is 0.47×10-6. The rate of mutation of the whole genome is taken into consideration to determine the ancestry,

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  1. The Y chromosome which is found in the nucleus, is also uniparentally inherited (like mtDNA), and is transmitted exclusively from father to son. Despite the higher per-base-mutation rate of mtDNA, the much greater length of the Y chromosome offers the highest genealogical resolution of all non-recombining loci in the human genome. The Y chromosome contains the longest stretch of non-recombining DNA in the human genome and is therefore a powerful tool with which to study human evolution.

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  1. The Y chromosome and the mitochondrial DNA (mtDNA) have been used to estimate when the common patrilineal and matrilineal ancestors of humans lived. The common ancestor of human patrilineal lineages is popularly referred to as the Y chromosome “Adam,” and the common ancestor of female lineages is called mitochondrial “Eve.” The time to the most recent common ancestor (TMRCA) of Y chromosome is 120–156 thousand years and the mtDNA TMRCA is 99–148 thousand years.

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  1. The ‘Out of Africa’ model is currently the most widely favoured explanation accounting for the origins of modern humans. It suggests that modern humans originated in Africa within the last 200,000 years from a single group of ancestors. Modern humans evolved in Africa possibly from Homo heidelbergensis, Homo rhodesiensis or Homo antecessor and migrated out of the continent some 50,000 to 100,000 years ago, gradually replacing local populations of Homo erectus, Denisova hominins, Homo floresiensis and Homo neanderthalensis. Unless modern human remains dating to 200,000 years ago or earlier are found in Europe or East Asia, it would seem that the replacement model better explains the fossil data for those regions. Studies of both the mitochondrial DNA (mtDNA) mismatch patterns in modern African populations and related mtDNA lineage-analysis patterns point to a major demographic expansion centered broadly within the time range from 80,000 to 60,000 B.P., probably deriving from a small geographical region of Africa. Most – but not all – genetic evidence appears to back the Out of Africa hypothesis. There is surprisingly little variation in the mitochondrial DNA (mtDNA) of different people today, which suggest that humans evolved recently from a small ancestral population. In addition, the variation of mtDNA in Africans is greater than elsewhere, suggesting that people have been evolving there for longer.

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  1. Modern humans and Neanderthals did interbreed, although on a very limited scale. Europeans and Asians share about 1-4% of their DNA with Neanderthals and Africans none. A sequencing of the Neanderthal genome in 2010 indicated that modern humans bred with Neanderthals after moderns left Africa but before they spread to Asia and Europe. The most likely location is the Levant, where both species co-existed for thousands of years at various times between 50-90,000 years ago. The interbreeding may have given modern humans genes that bolstered immunity to pathogens. Neanderthals interbred with another species, the Denisovans, as did some of modern humans. Some people from South East Asia have up to 6% Denisovan DNA.

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  1. The number of archaic humans whose DNA has been analyzed and published till March 2018 is 1336. The new flood of genetic information represents a “coming of age” for the nascent field of ancient DNA. The startling revelation from the ancient DNA is that that human populations are moving and mixing all the time and people moved, all the way to the Atlantic coast of Europe in the west, to Mongolia in the east, and India in the south.

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  1. Several classes of evidence, morphological, molecular, and genetic, support a particularly close relationship between modern humans and the species within the genus Pan, the chimpanzee. Existing DNA sequence data sets provide overwhelming and sufficient support for a human-chimpanzee clade; and the problem of hominoid phylogeny can be confidently considered solved. Comparison of chimpanzee genetic blueprints with that of the human genome shows that our closest living relatives share 96 percent of our DNA i.e. 96 % of the nucleotide sequences of the modern human and chimpanzee genomes are identical. Despite similarities in human and chimp genomes, there are ∼35 million single nucleotide differences and ∼90 Mb of insertions and deletions. The vast majority of those differences are not biologically significant, but a couple thousand differences that are potentially important to the evolution of the human lineage. The morphological and behavioral differences between humans and chimpanzees are predominately due to differences in the regulation of genes rather than to differences in the sequence of the genes themselves. But changes in gene regulation are probably not sufficient to explain all the differences between chimps and humans. There is evidence that core duplicons are a driving force behind human evolution from common ancestor. Core duplicons are stretches of DNA that appear over and over on a specific chromosome.

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  1. Forkhead box protein P2 (FOXP2) is a protein that, in humans, is encoded by the FOXP2 gene, and is required for proper development of speech and language. Neanderthal shared the same version of a gene FOXP2 with modern humans. This gene appears in different forms in other vertebrates where it performs a slightly different function. This suggests the gene mutated not long before the split between the Neanderthals and modern human lines. When complementary DNAs that encode the FOXP2 protein in the chimpanzee, gorilla, orang-utan, rhesus macaque and mouse was compared them with the human complementary DNA, it showed that human FOXP2 contains changes in amino-acid coding and a pattern of nucleotide polymorphism, which strongly suggest that this gene has been the target of selection during recent human evolution.

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  1. Although humans and African apes share common ancestor 7 million years ago, African apes are still around because their environment has encouraged the reproductive success of individuals with different genetic material than ours.

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  1. Emotions are adaptive programs designed through repeated encounters that are intended to either direct other physiological programs or to directly solve adaptive problems faced by a species over time. Universal expressions of emotions (anger, fear, disgust, sadness, and enjoyment) do not necessarily prove Darwin’s theory that they evolved, but they do provide strong evidence of the possibility.

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  1. Culture, cultural transmission, and cultural evolution arise from genetically evolved psychological adaptations for acquiring ideas, beliefs, values, practices, mental models, and strategies from other individuals by observation and inference. These cognitive adaptations give rise to another system of inheritance (cultural evolution) that operates by different transmission rules than genetic inheritance. Cultural evolution can alter both the social and physical environments faced by evolving genes, leading to a process termed culture-gene coevolution. Cultural and biological forms of evolution are better regarded as a single integrated process than as separate influences on human populations. Evidence from genetics suggests that culture has long shaped our genome.

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  1. Evolution explains socially useful behavior in animals, and morality with its thoughts about right or wrong, in human beings. Human’s enhanced ability to cooperate with each other, coupled with shared intentionality gave humans the morality.

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  1. Evolution explains nepotism and despotism in humans. Individuals gain inclusive fitness benefits from cooperating with relatives, because the costs of helping is outweighed by the increased fitness of individuals with whom they share genes identical by decent. Voluntary leadership without coercion can evolve in small groups but transition to larger despotic groups will occur when surplus resources lead to demographic expansion of groups locking individuals into hierarchy; and high dispersal costs limit followers’ ability to escape a despot.

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  1. There is evidence to show that humans are still evolving albeit slowly, especially compared with the rapid changes that have occurred over the past few generations due to cultural, technological and environmental factors. Human genome is constantly reshaped by natural selection, and natural selection continues to weed out disadvantageous traits even today. Besides natural selection, artificial selection and genetic drift also contribute to human evolution. On the other hand, humans can cause evolution by changing climate/environment and letting natural selection to work, and also by artificial selection.

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  1. Evolution explains epidemic of lifestyle diseases like obesity, hypertension, diabetes and heart diseases. The current dietary pattern (fast food and junk food), characterized by high intakes of sugar, flours, salt and refined fats coupled with sedentary lifestyles has never happened at any time in our evolutionary history. There is gross mismatch between our current lifestyles and those of our ancestors whose genes we carry and it will take lot of time for these genes to adapt to current lifestyle. We eat far more food and burn far fewer calories than that at any other point in our evolutionary history. The only option before us is to avoid fast food and junk food, and do exercise rather than wait for our genes to adapt as human genome changes fairly slowly.

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  1. Evolution is a historical science confirmed by the fact that so many independent lines of evidence converge to this single conclusion. Independent sets of data from geology, paleontology, botany, zoology, biogeography, comparative anatomy and physiology, genetics, molecular biology, developmental biology, embryology, population genetics, genome sequencing, and many other sciences each point to the conclusion that life evolved. No single discovery from any of these fields denotes proof of evolution, but together they reveal that life evolved in a certain sequence by a particular process. Evolution is a well-supported and broadly accepted scientific theory; the only well-supported explanation for life’s diversity because of the multiple lines of evidence supporting it, its broad power to explain biological phenomena, and its ability to make accurate predictions in a wide variety of situations. Researchers are constantly revising the narrative of evolution as new discoveries of fossils/ancient DNA are made and new technologies of dating are available. So different researchers come out with different chronology, different phylogeny, different dispersal patterns and different nomenclature as evident in this article but that is how science works. Evolution is not conundrum but the subject is so vast and so many disciplines are involved in research that connecting dots to make big picture is difficult.

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  1. Applications of evolution are important in medicine, agriculture, forensics, bioengineering etc. Evolution is helpful in studying and combating antimicrobial resistance, vaccine development, drug development, genetic disorders etc.

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  1. Biologists have argued for an extended evolutionary synthesis retaining the fundaments of evolutionary theory, which would account for the effects of non-genetic inheritance modes such as epigenetics, parental effects, ecological and cultural inheritance; plus the microbiome, regulation of gene expression and evolvability to fully comprehend evolution.

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  1. Adaptation takes place through direct genetic modifications in response to environmental stress (i.e. evolution). However, many animal species are able to accommodate environmental stress simply by changing their behaviour in response to environmental conditions, without the need to resort to genetic adaptation. If behavioural flexibility cannot accommodate environmental stress, animals also have a range of physiological mechanisms that help them to respond—again, without the need for genetic adaptation. So organisms do adapt to their environment in a way that does not necessarily has anything to do with genetics. Besides behavioural and physiological flexibility, humans (due to great cognitive power) have developed culture and technology that has allowed them to populate the most extreme environments worldwide, again without the need for genetic adaptation. Culture and technology allow humans to have greater control of their environment, rather than responsive to it. Thus, the development of these skills would directly contribute to the survival of individuals (& groups) practising these behaviours. In other words, although we the humans are evolving biologically, our culture and technology can help us tackle environmental stresses without use of biological evolution. Natural selection will continue to operate in humans; but human culture and technology also work side by side to ensure survival and reproduction; not to mention that culture is also shaping our genome in gene-culture coevolution.

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  1. Richard Dawkins defines evolution as “random mutation plus non-random cumulative selection,” and it is the cumulative selection that drives evolution. Although cumulative selection does drive evolution but you can select only if there is genetic variation to select and that genetic variation comes only by chance. Also chance plays an important role even in the process of the elimination of less fit individuals, and particularly during periods of mass extinction. So life evolved and continues to evolve predominantly by chance. There is certainly no element of direction. Living things are just trying to adapt to the contingencies of life in their environment. Evolution is only “directed” in that it favours survival and reproduction by on-going process of trial and error. It is natural to think of humans as “more evolved” than other animals, but this isn’t true in any scientific sense. We are differently evolved, simply adapted to a different environment. It so happened that our intelligence, and the culture and technology that it spawned has turned out to allow us an unprecedented degree of success, and the ability to live in environments that our ancestors couldn’t. But evolution didn’t somehow anticipate this. Evolution does not favor high intelligence or walking upright or use of tools, unless these features aid in the survival and passing on of genes to the next generation.

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Dr. Rajiv Desai. MD.

April 4, 2018

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Postscript:

Those who deny evolution are either ignorant or misinformed or unintelligent or fundamentalist.

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