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Human originsHuman evolution, or anthropogenesis, is the part of biological evolution concerning the emergence of Homo sapiens as a distinct species from other hominins, great apes and placental mammals. It is the subject of a broad scientific inquiry that seeks to understand and describe how this change occurred. The study of human evolution encompasses many scientific disciplines, most notably physical anthropology, primatology, archaeology, linguistics and genetics. The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually include other hominins, such as the Australopithecines. The Homo genus diverged from the Australopithecines about 2 million years ago in Africa. Scientists have estimated that humans branched off from their common ancestor with chimpanzees—the only other living homininis—about 5–7 million years ago. Several "species" of Homo evolved or are now extinct. These include Homo erectus, which inhabited Asia, and Homo neanderthalensis, which inhabited Europe. Archaic Homo sapiens evolved between 400,000 and 250,000 years ago. The dominant view among scientists was the recent African origin of modern humans (RAO) that H. sapiens evolved in Africa and spread across the globe, replacing populations of H. erectus and H. neanderthalensis. Scientists supporting the alternative hypothesis, multiregional evolution (ME), view modern humans as having evolved as a single, widespread population from existing Homo species, particularly H. erectus. The fossil evidence were insufficient to Leakey to resolve this vigorous debate,. Studies of haplogroups in Y-chromosomal DNA and mitochondrial DNA have largely supported a recent African origin, while evidence from nuclear genes supports a multiregional evolution. 2009 statistical analysis over available NIH data find evidence for ancient admixture, suggesting this may be a general feature of recent human evolution History of ideas about human evolutionThe word homo, the name of the biological genus to which humans belong, is Latin for "human". It was chosen originally by Carolus Linnaeus in his classification system. The word "human" is from the Latin humanus, the adjectival form of homo. The Latin "homo" derives from the Indo-European root, dhghem, or "earth". Carolus Linnaeus and other scientists of his time also considered the great apes to be the closest relatives of human beings due to morphological and anatomical similarities. The possibility of linking humans with earlier apes by descent only became clear after 1859 with the publication of Charles Darwin's On the Origin of Species. This 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 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 agree that the origin of the mental capacities and the moral sensibilities of humans could be explained by natural selection. Darwin applied the theory of evolution and sexual selection to humans when he published The Descent of Man in 1871. A major problem was the lack of fossil intermediaries. It was only in the 1920s that such fossils were discovered in Africa. In 1925, Raymond Dart described Australopithecus africanus. The type specimen was the Taung Child, an Australopithecine infant discovered in a cave. The child's remains were a remarkably well-preserved tiny skull and an endocranial cast of the individual's brain. Although the brain was small (410 cm³), 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 was evidence of bipedal locomotion. All of these traits convinced Dart that the Taung baby was a bipedal human ancestor, a transitional form between apes and humans. The classification of humans and their relatives has changed considerably over time. The Australopithecines are now thought to be ancestors of the genus Homo, the group to which modern humans belong. Both Australopithecines and Homo sapiens are part of the tribe Hominini. Recent data suggests Australopithecines were a diverse group and that A. africanus may not be a direct ancestor of modern humans. Reclassification of Australopithecines that originally were split into either gracile or robust varieties has put the latter into a family of its own, Paranthropus. Taxonomists place humans, Australopithecines and related species in the same family as other great apes, in the Hominidae. Before HomoEvolution of apesThe evolutionary history of the primates can be traced back 65 million years, as one of the oldest of all surviving placental mammal groups. The oldest known primates come from North America, but they were widespread in Eurasia and Africa during the tropical conditions of the Paleocene and Eocene. With the beginning of modern climates, marked by the formation of the first Antarctic ice in the early Oligocene around 30 million years ago, primates went extinct everywhere but Africa and southern Asia. A primate from this time was Notharctus. Fossil evidence found in Germany in the 1980s was determined to be about 16.5 million years old, some 1.5 million years older than similar species from East Africa. It suggests that the primate lineage of the great apes first appeared in Eurasia and not Africa. The early ancestors of the hominids (the family of great apes and humans) probably migrated to Eurasia from Africa about 17 million years ago, just before these two continents were cut off from each other by an expansion of the Mediterranean Sea. Begun says that these primates flourished in Eurasia and that the lineage leading to the African apes and humans— including Dryopithecus—migrated south from Europe or Western Asia into Africa. The surviving tropical population, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Fayum depression southwest of Cairo, gave rise to all living primates—lemurs of Madagascar, lorises of Southeast Asia, galagos or "bush babies" of Africa, and the anthropoids; platyrrhines or New World monkeys, and catarrhines or Old World monkeys and the great apes and humans. The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya Rift Valley, dated to 24 million years ago. Its ancestry is generally thought to be species related to Aegyptopithecus, Propliopithecus, and Parapithecus from the Fayum, at around 35 million years ago. There are no fossils from the intervening 11 million years. In the early Miocene, after 22 million years ago, the many kinds of arboreally-adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the earliest Old World Monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa. The presence of other generalized non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene. The youngest of the Miocene hominoids, Oreopithecus, is from 9 million year old coal beds in Italy. Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) became distinct from Great Apes between 18 and 12 million years ago, and that of orangutans (subfamily Ponginae) became distinct from the other Great Apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Ramapithecus from India and Griphopithecus from Turkey, dated to around 10 million years ago. Divergence of the human lineage from other Great ApesSpecies close to the last common ancestor of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the chimpanzees (genus Pan) split off from the line leading to the humans; human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms (see Human evolutionary genetics). The fossil record of gorillas and chimpanzees is quite limited. Both poor preservation (rain forest soils tend to be acidic and dissolve bone) and sampling bias probably contribute to this problem. Other hominines likely adapted to the drier environments outside the equatorial belt, along with antelopes, hyenas, dogs, pigs, elephants, and horses. The equatorial belt contracted after about 8 million years ago. Fossils of these hominans - the species in the human lineage following divergence from the chimpanzees - are relatively well known. The earliest are Sahelanthropus tchadensis (7 Ma) and Orrorin tugenensis (6 Ma), followed by:
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