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In paleoanthropology, the recent African origin of modern humans, or the "out of Africa" theory (OOA), is the most widely accepted model of the geographic origin and early migration of anatomically modern humans. The theory is called the "out-of-Africa" theory in the popular press, and the "recent single-origin hypothesis" (RSOH), "replacement hypothesis", or "recent African origin model" (RAO) by experts in the field. The concept was speculative before it was corroborated in the 1980s by a study of present-day mitochondrial DNA, combined with evidence based on physical anthropology of archaic specimens. Genetic studies and fossil evidence indicate that archaic humans evolved to anatomically modern humans solely in Africa between 200,000 and 60,000 years ago, that members of one branch of ''Homo sapiens'' left Africa at some point between 125,000 and 60,000 years ago, and that over time these humans replaced other populations of the genus Homo such as Neanderthals and ''Homo erectus''. The date of the earliest successful "out of Africa" migration (earliest migrants with living descendants) has generally been placed at 60,000 years ago based on mitochondrial genetics, but this model has recently been contested by simulations of mitochrondrial DNA data,〔 〕 125,000-year-old Arabian archaeological finds of tools in the region and the discovery of ''Homo sapiens'' teeth in China, dating to at least 80,000 years ago. The recent single origin of modern humans in East Africa is the predominant position held within the scientific community. There are differing theories on whether there was a single exodus or several. An increasing number of researchers think that "long-neglected North Africa" may have been the original home of the first modern humans to migrate out of Africa. The major competing hypothesis is the multiregional origin of modern humans, which envisions a wave of ''Homo sapiens'' migrating earlier from Africa and interbreeding with local ''Homo erectus'' populations in multiple regions of the globe. Most multiregionalists still view Africa as a major wellspring of human genetic diversity, but allow a much greater role for hybridization. Genetic testing in the last decade has revealed that several now extinct archaic human species may have interbred with modern humans. These species have been claimed to have left their genetic imprint in different regions across the world: Neanderthals in all humans except Sub-Saharan Africans, Denisova hominin in Australasia (for example, Melanesians, Aboriginal Australians and some Negritos) and there could also have been interbreeding between Sub-Saharan Africans and an as-yet-unknown hominin (possibly remnants of the ancient species Homo heidelbergensis). However, the rate of interbreeding was found to be relatively low (1–10%) and other studies have suggested that the presence of Neanderthal or other archaic human genetic markers in modern humans can be attributed to shared ancestral traits originating from a common ancestor 500,000 to 800,000 years ago.〔()〕〔http://www.theguardian.com/science/2013/feb/04/neanderthals-modern-humans-research〕〔()〕〔(The Human Stew )〕〔http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1002837〕 ==History of the theory== With the development of anthropology in the early 19th century, scholars disagreed vigorously about different theories of human development. Those such as Johann Friedrich Blumenbach and James Cowles Prichard held that since the creation, the various human races had developed as different varieties sharing descent from one people (monogenism). Their opponents, such as Louis Agassiz and Josiah C. Nott, argued for polygenism, or the separate development of human races as separate species or had developed as separate species through transmutation of species from apes, with no common ancestor. Charles Darwin was one of the first to propose common descent of living organisms, and among the first to suggest that all humans had in common ancestors who lived in Africa. Darwin first suggested the "Out of Africa" hypothesis after studying the behaviour of African apes, one of which was displayed at the London Zoo. The anatomist Thomas Huxley had also supported the hypothesis and suggested that African apes have a close evolutionary relationship with humans. These views were however opposed by Ernst Haeckel the German biologist who was a proponent of the Out of Asia theory. Haeckel argued that humans were more closely related to the primates of Southeast Asia and rejected Darwin’s hypothesis of Africa. In the ''Descent of Man'', Darwin speculated that humans had descended from apes which still had small brains but walked upright, freeing their hands for uses which favoured intelligence. Further, he thought such apes were African: The prediction was insightful, because in 1871 there were hardly any human fossils of ancient hominids available. Almost fifty years later, Darwin's speculation was supported when anthropologists began finding numerous fossils of ancient small-brained hominids in several areas of Africa (list of hominina fossils). The debate in anthropology had swung in favour of monogenism by the mid-20th century. Isolated proponents of polygenism held forth in the mid-20th century, such as Carleton Coon, who hypothesized as late as 1962 that ''Homo sapiens'' arose five times from ''Homo erectus'' in five places. The "Recent African origin" of modern humans means "single origin" (monogenism) and has been used in various contexts as an antonym to polygenism. In the 1980s Allan Wilson together with Rebecca L. Cann and Mark Stoneking worked on the so-called "Mitochondrial Eve" hypothesis. In his efforts to identify informative genetic markers for tracking human evolutionary history, he started to focus on mitochondrial DNA (mtDNA) – genes that sit in the cell, but not in the nucleus, and are passed from mother to child. This DNA material is important because it mutates quickly, thus making it easy to plot changes over relatively short time spans. By comparing differences in the mtDNA Wilson thought it was possible to estimate the time, and the place, modern humans first evolved. With his discovery that human mtDNA is genetically much less diverse than chimpanzee mtDNA, he concluded that modern human populations had diverged recently from a single population while older human species such as Neandertals and ''Homo erectus'' had become extinct. He and his team compared mtDNA in people of different ancestral backgrounds and concluded that all modern humans evolved from one 'lucky mother' in Africa about 150,000 years ago.〔(【引用サイトリンク】 Allan Wilson: Revolutionary Evolutionist )〕 With the advent of archaeogenetics in the 1990s, scientists were able to date the "out of Africa" migration with some confidence. 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, supports the multiregional origin of modern humans hypothesis.〔(Australia Challenges Out-of-Africa Theory ) ABC News January 9, 2003〕 This work was later questioned and explained by W. James Peacock, leader of the team who sequenced Mungo man's aDNA. In addition, a large-scale genotyping analysis of aboriginal Australians, New Guineans, Southeast Asians and Indians in 2013 showed close genetic relationship between Australian, New Guinean, and the Mamanwa people, with divergence times for these groups estimated at 36,000 y ago. Further, substantial gene flow was detected between the Indian populations and aboriginal Australians, indicating an early "southern route" migration out of Africa, and arrival of other populations in the region by subsequent dispersal. This basically opposes the view that there was an isolated human evolution in Australia. The question of whether there was inheritance of other typological (not ''de facto'') ''Homo'' subspecies into the ''Homo sapiens'' genetic pool is debated. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Recent African origin of modern humans」の詳細全文を読む スポンサード リンク
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