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Geneticists have found out why the ancestors of humans interbred with Neanderthals
Contacts with Neanderthals helped the ancestors of modern man to acquire protection from "Eurasian" viruses that did not exist in Africa. This accelerated the colonization of the planet and helped Cro-Magnons become the dominant species on Earth, scientists write in an article published in the journal Cell (David Enard, Dmitry A. Petrov. Evidence that RNA Viruses Drove Adaptive Introgression between Neanderthals and Modern Humans).
"Many traces of Neanderthal DNA have already disappeared from the human genome, while others have not disappeared anywhere and have even become very common among our ancestors, which indicates an obvious benefit for them. We tried to understand what their advantages were. It turned out that they made humanity more resistant to the action of certain RNA viruses," Dmitry Petrov from Stanford University said (in a press release Viruses influenced gene sharing between Neanderthals and humans - VM).
Despite the external similarity, modern humans and Neanderthals developed in different ways. They separated about 650 thousand years ago. The former stayed in Africa and gradually colonized it, the latter migrated north and settled Europe and Asia.
For a long time it was believed that humans and Neanderthals have nothing in common, but in 2009, scientists restored the genome of the first aborigines of Europe and found that the DNA of most modern people, in addition to the inhabitants of Africa, contains three to four percent of Neanderthal genes. This fact made scientists wonder how contacts between the ancestors of humans and Neanderthals could have occurred and why traces of their DNA were preserved in our genome.
Many scientists today believe that Neanderthal DNA improved the immunity of our ancestors, but how exactly this happened, geneticists did not know until now. Petrov and his colleague David Enard from The University of Arizona in Tucson (USA) tried to solve this mystery by studying the structure of Neanderthal segments of the human genome.
In this analysis, the researchers relied on a simple consideration. If a certain section of DNA is very useful, then it should quickly spread among all representatives of the population in approximately the same form.
Later, these segments of the genome had to be broken down into smaller and more diverse fragments combining human and Neanderthal DNA. If the segment is useless or harmful, then it will either disappear completely from the gene pool, or it will remain in a less fragmented and diverse form.
Accordingly, by comparing and combining the genomes of different people, it is possible to obtain the "original" DNA chain inherited from Neanderthals, and to understand by the number of its fragments how much our ancestors needed it.
Guided by this idea, the scientists analyzed the structure of approximately 4,500 genes associated with the work of immunity. As it turned out, the largest number of Neanderthal DNA segments and the highest diversity in their structure are characteristic of 100-120 genome sites associated with protection against RNA viruses.
A picture from an article in Cell – VM.
These sections of DNA, as geneticists suggest, helped our ancestors quickly adapt to life in new territories and avoid mass epidemics.
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