Evidence now for at least five admixture breedings among Neanderthal, Denisovian and Modern human lineages

It has been established for several years that small portions of the European and Asian genomes are derived from Neaderthals, a subline that was “not successful” and therefore “died out” at least 28,000 years ago. This most recent report [attached] now details further admixture––that had occurred during the past 60,000 years––between modern human (Homo sapiens sapiens) and both Neaderthals (Homo neaderthalensis, first found in the Neader River Valley of Germany and became extinct between 40,000 and 28,000 years ago) and Denisovians (Homo denisoviensis, bones found in Altai Mountains of southern Siberia ~41,000 years ago).

By developing powerful new statistical methods, an international team has identified how often, and on which continents, … Eurasians, Neanderthals, and Denisovans met and mated. The researchers conclude that––if you are an East Asian––you have three Neanderthals in your family tree; Europeans and South Asians have two, and Melanesians only one. Africans, whose ancestors preceded any of the migrations “Out of Africa”, did not mate with Neanderthals, and therefore have none (however, there are reports of Neaderthal genes in some samples of modern man, having some Neanderthal genes, who had “back-migrated” south into Africa).

Considering these two newly discovered interbreedings––established only from fossil DNA––we can conclude that the ancestors of modern humans and Neanderthals have interbred at least five times. Meanwhile, the Denisovans bred at least once with Melanesians (those from a subregion of Oceania extending from the western end of the Pacific Ocean to the Arafura Sea, and eastward to Fiji), and these interbreedings appear to be separate events.

This exciting new approach––to identify DNA inherited from multiple archaic hominin ancestors and applying that information to whole-genome sequences––was carried out on 1,523 geographically diverse individuals, including 35 new Island Melanesian genomes. In aggregate, the international research team recovered 1.34 Gb (billion bases) and 303 Mb (million bases of the Neanderthal and Denisovan genome, respectively. They leveraged these maps of archaic sequence to show that Neanderthal admixture occurred multiple times in different non-African populations, characterized genomic regions that are significantly depleted of archaic sequence, and identified signatures of adaptive introgression.

Science  10.1126/science.aad9416 (2o16) … & editorial in Science  2o16; 351: 1250–1251

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