A new method for analyzing genomes made it possible to find traces of Neanderthal DNA in the native inhabitants of Africa, although before they were considered “pure sapiens”.
The genome of modern African inhabitants has preserved far more traces of Neanderthal DNA than scientists have so far considered. Our direct ancestors met and sometimes began to interbreed with them, leaving Africa to Eurasia between 50 and 80 thousand years ago. However, waves of later reverse migrations brought some Neanderthal genes to the Black Continent. This conclusion was reached by the authors of the new articles published in the journal Cell.
Recall that Neanderthals were the closest relatives of H. sapiens, who inhabited part of Europe and Asia long before the appearance of our ancestors here – from 800 thousand years ago. They disappeared about 40 thousand years ago, but managed to meet a large wave of sapiens, so the DNA of modern people outside of Africa by 1.5-2 percent is Neanderthal. It was believed that only the “indigenous” inhabitants of sub-Saharan Africa remained “pure” sapiens. However, modern Africans have such traces – about 0.5 percent of Neanderthal DNA.
The fact is that before, to search for Neanderthal fragments in the DNA of modern people, they were compared with each other, as well as with the DNA of modern representatives of African tribes (for example, the Yoruba peoples from Nigeria) – as a “reference”. It is believed that they did not interact with Neanderthals at all and did not save any traces in the DNA. However, if this is not so, then such a comparison invariably distorted the results of any comparisons.
To get rid of this distortion, Princeton geneticist Joshua Akey and his colleagues proposed a new method for statistical analysis of genomes. IBDmixthat does not require a “reference” population. Scientists have collected DNA samples from 2,500 inhabitants of Africa, Europe and the Far East, comparing them with previously obtained data on the genomes of Neanderthals, the remains of which were found in southern Europe and Siberia.
Such work found in Africans about 0.5 percent of Neanderthal DNA. More than 94 percent of these fragments are also found in the genome of the inhabitants of Eurasia, indicating that they were received later – from them, and not directly from Neanderthals. These genes affect the functioning of the immune system and UV protection, so they seem to quickly gain a foothold and spread throughout Africa.
A new perfect analysis method allowed us to distinguish between the more curious details of the human genome and the past. So, scientists have shown that part of the Neanderthal DNA that we have preserved was obtained by them from an older wave of sapiens who left Africa between 150 and 100 thousand years ago. During the following migrations – already back to Africa, starting from 20 thousand years ago – some of these fragments again “returned” to the genome of our ancestors.
In total, in modern European populations, IBDmix counted 1.7 percent of Neanderthal DNA, in the Far East – 1.8 percent. A small amount of the Neanderthal genome, which then appeared again in Africa, is noticeably closer to the part that was preserved among Europeans. This indicates that it was from them that the Africans received the DNA of our common extinct relatives not so long ago.