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Population Genetics (numbers are Millennia before present); The letters on the arrows represent groups of people belonging to the same mitochondrial Haplogroup . Haplogroups are a type of genetic categorization that groups people together base on shared variation in their mitochondrial DNA.]] PRE-MODERN (NON-''SAPIENS'') HOMINIDS Because of the scarcity of Fossil s and the discovery of important new finds every few years, researchers disagree about the details and sometimes even basic elements of Human Evolutionary History . While they have revised this history several times over the last decades, researchers currently agree that the oldest named Species of the genus '' Homo '', '' Homo Habilis '', evolved in Africa around two million years ago, and that members of the genus migrated out of Africa somewhat later. The descendants of these ancient migrants, which probably included '' Homo Erectus '', have become known through fossils uncovered far from Africa, such as those of " Peking Man " and " Java Man ". The '' Homo Neanderthalensis '' is also considered a descendant of early migrants. AFRICAN EVIDENCE OF "MODERN" HUMANS According to the single-origin model, however, every species of the genus ''Homo'' but one, '', at Omo River ( Ethiopia ), previously thought by Richard Leakey to date to about 130,000 years ago, on the basis of careful re-examination of Potassium-argon Dating at Omo 1, is now thought to date to 195,000 years ago, making it a good candidate to be a site type for AMH ancestors. Genetically, ethnically, linguistically and now archaeologically four distinct African populations on the basis of the L0 mutation in mtDNAcan within the human genome can be determined:
The warm Interglacial and the green Sahara allowed humans living in Ethiopia and the southern Sudan to travel north, crossing the Sinai Peninsula into modern Israel 115,000 years ago. This forms the basis of the Sahul populations found in this area. A sudden freezing of the world’s climates in about 90,000 years ago, saw the return of severe arid conditions to the Middle East, with the loss of major game, and when the dry spell ended, the cold conditions saw the replacement of anatomically modern humans found at Jebel Qafseh in Israel , with cold adapted Neanderthal populations some of which have been found at Skhul in the Mount Carmel caves. [http://www.genetics.org/cgi/rapidpdf/genetics.105.041095v1 Research on the X chromosome] claims to be the first genetic evidence against this model, suggesting an alternative model incorporating admixture between divergent African branches of the genus ''Homo''. SINGLE EXODUS FROM AFRICA? Assuming only relatively recent migrants from Africa gave rise to today's non-African humans, was there more than one migration that left descendants? (for example, one each via the north and south ends of the Red Sea ) There are two possible routes out of Africa. 1. The first and most obvious one is from Egypt, across the Sinai into the Levant . This route is confronted by the major impediment of the arid zone of the Sahara and Sinai deserts, and thus tends to be only passable during the short periods of Interglacial Optimum when the Sahara is covered by fresh water lakes, rivers and abundant game. 2. The second route, only opened when sea levels fall is across the Bab-el-Mandeb , between Yemen and Djibouti . This route too is confronted by a barrier, this time the Red Sea and its hazardous reefs, and so is usually only opened when there is a major fall in sea levels. Although, humans must have had ocean-going vessels at least 60,000 years ago to reach Australia, which was separated by hundreds of miles of ocean even at the ocean's lowest level, so it is also possible that humans had vessels capable of crossing a gap of ocean at the strait of Aden not long earlier. This area, at the times at which sea levels were low, is also an area of high aridity, probably keeping a beachcombing human population close to the ancient shorlines, now well below sea-level, making the finding of early human fossils here very difficult.
Low glacial sea levels at this period would have been the first time in millennia permitting a dry walk from the Gulf of Aden to the islands East of Java facing Australia. Among Y-chromosomal haplogroups, the M130 and the M174 YAP gene haplogroups in particular confirm this hypothesis as their path traces a great arc along the shorelines of Saudi Arabia , India , South East Asia and Australia . This beachcomber culture moved on through southern China, and Taiwan to Japan and Eastern Siberia. There about 8-10,000 years ago the M130 haplogroup was carried by Na-Dené speaking peoples into the North West Pacific coast of America .
MULTIREGIONAL HYPOTHESIS The opponents of a single origin argue that interbreeding indeed occurred, and that the characteristics of modern humans, including those that have been and still are perceived by some to distinguish Race s, could only be the result of genetic contributions from several earlier lineages that evolved semi-independently in different parts of the world. This is the " Multiregional Hypothesis ", including the Hybrid-origin theory. While the genetic evidence is making this theory increasingly hard to support, it is politically attractive to some groups who see it as a way of establishing a much more ancient claim of connection of habitation of their area; for example, the idea of descendency of modern Chinese from Peking Man is promoted by the government of the People's Republic Of China . PROPONENTS OF THE SINGLE-ORIGIN HYPOTHESIS SEE ALSO FURTHER READING
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