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Bottleneck Genes

12 November 2016

The Neanderthal/Denisovan surviving genes in modern humans has been taken up at http://popular-archaeology.com/issue/fall-2016/article/evolution-purged-… … which again implies that the genetic inheritance from archaic humans such as the Neanderthals and Denisovans, has gradually been diluted as the modern human genome has evolved in the intervening years – over 30,000 years. However, little pieces of them live on in modern genes – but the inference is that they have grown smaller and smaller as time has progressed. The assumption central to the story (and the research) is that modern humans advanced Out of Africa between 50,000 (most of us) and 80,000 (Aborigines and some other isolated groups) years ago. They interbred with archaic humans and inherited some of their genes – which as a result of the disappearance of the archaics has meant modern human genes have been able to dominate and phase out the archaic genes. What we have nowadays is a relic of the archaic genes.

It seems small groups of archaic humans may have survived in pockets long enough to interbreed with modern humans. One is then left with a storyline that although Neanderthals and Denisovans disappeared (by 30,000 years ago) they were able to interbreed with the newcomers (before their demise). We may wonder if there really was a lot of newcomers as a bottleneck situation could explain the survival of archaic genes just as easily as Out of Africa. This would require a reappraisal of the Australian Aborigines too as they must have been subject to the same bottleneck as large numbers of animals disappeared in a mass die-off event between 40,000 and 30,000 years ago. The interesting thing is that Neanderthals occupied the same geographical region that was later occupied by the initial migration of modern humans (Europe and large parts of Asia – such as the Near and Middle East).

At http://phys.org/print397992390.html … the headline asks – did Neanderthal genes help modern humans to survive in Euro-Asia (presumably a reference to cold weather during the final stages of the Ice Age). This link comes from a study published in Current Biology (Nov 10th 2016) (www.cell.com/current-biology/fulltext/S0960-9822(16)31267_2 and says that there are 126 different places in the genome with genes inherited from archaics. The earlier paper is at PLoSGent 12 (11) ie1006340

All we know really is that something extraordinary happened 30,000 years ago (possibly a double whammy). Not only was there a mass die off but it probably included a mass die-off of Middle Palaeolithic humans. The Late Paleolithic humans that went on to multiply are the offspring of the survivors – whether we consider Euro-Asia or Africa (or Australia). See also http://popular-archaeology.com/issue/fall-2016/article/neanderthal-inher…  

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