By comparing individual DNA letters in multiple modern human genomes with those in the Neanderthal genome, the date of that interbreeding has now been pinned down to 65,000–90,000 years ago. Montgomery Slatkin and Anna-Sapfo Malaspinas, theoretical geneticists from the University of California, Berkeley, presented the finding at the Society for Molecular Biology and Evolution meeting in Kyoto, Japan, held on 26–30 July.But more information about that hybridization has recently come to light:
Interbreeding endowed humans with a 'hybrid vigour' that helped them colonize the world, said Peter Parham, an immunogeneticist at Stanford University School of Medicine, California, at the symposium.The Denisova genome, if you will remember, represents a slightly different strain than that of either modern humans or Neandertals, although probably not a separate species. Here is the graphic in Nature News that shows possible migration routes.
Parham's team compared a group of diverse immune genes — the human leukocyte antigen (HLA) genes — in Neanderthals, Denisovans and human groups from around the world. In several cases, Neanderthals and Denisovans carried versions of HLA genes that are abundant in modern humans in parts of Europe and Asia, but less common in Africans. Varying degrees of interbreeding could explain the mismatch, Parham says. He estimates that Europeans owe 50% of variants of one class of HLA gene to interbreeding, Asians 70–80%, and Papua New Guineans up to 95%.
R.I.P.: Out-of-Africa Replacement model
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