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Tuesday, May 29, 2012

Denisovan Admixture stretches back from 3 million years

Various reports disagree on the date the Denisovan split from the line that led to modern man, and the biggest discrepancies stem mainly from which Denisovan-like genes are being studied, and not from which dating methods were used. I propose this is because the Denisovan genome was is a giant gene dump: the Denisovan hominid was a mutt and various types of hominid in Asia were undergoing muttinization just before and at the time of Hss take-over. Homo erectus and similar forms had lived in Asia for probably two million years. Some of their deepest DNA lineages had been separated from those that led directly to us by over 2 million years. Around 225 thousand years ago a descendant of heidelbergensis finally pushed into the coastal regions of mainland East Asia and bean to absorb the erectines there. Like his cousins in Africa that now make up only 2% of the genes there, his deepest lines had been separated from our line by some 700,000 years, while some lines may have had onlt 2-400,000 years of separation from ours. So Asia from the Altai region all the way down to the Wallace line was undergoing heidelberg/erectus hybridization to various degrees until around 120,000 years ago when an anatomically modern homo sapien line which was, nonetheless, not descended from the line of Mitochondrial Eve entered East Asia from South Asia and supplanted/interbred with Denisovans along the Southern coasts of the mainland. By 60, 000 years ago he had made it from East Asian coast through Eastern Sundaland all the way to the southern tip of Australia, but had not fully absorbed the Denisovan populations in Western Sundaland and surrounding Islands and in the interior of China. The Toba eruption separated eastern "Mungo Man" from the descendants of Mitochondrial Eve, who had been were pressing them east in India, and also devastated erectus populations in Sundaland. Around 40,000 ybp our ancestors, presumably with many males carrying genes ancestral to Y-haplogroup C as well as neanderthal genes from admixture in South West Asia, made it intop East Asia following the same path as Mungo Man and absorbing him as he went. This is were the early C Haplogroups got the Denisovan genes, and further studies will likely reveal that populations with a lot of Denisovan genes will also yield a higher than normal amount of genes from humans that seperated from our line after Neanderthal and Denisovan divurgence, but BEFORE the birth of Mitochondrial Eve. In short,the Denisovan gene is a hodge-podge of of evolutionary lines that descended from South and East Asian representatives of homo erectus, heidelbergensis, neanderthal (via hybridization in the Altai region), archaic homo sapien, and possibly even "Mungo Man" and direct eastern descendants of homo georgicus. It would be interesting to see if populations with Denisovan genes also have a high degree of Mungo Man's DNA embedded in their chromosome. Source Blog
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