Interbreeding with Neanderthals: Source of Modern Human Viral Defences?

Neanderthals might have disappeared from the world some 40,000 years back, but in the process of interbreeding with the modern humans, they passed some of their DNAs to the modern human species. Remnants of these ancient trysts are still present in today’s European and Asian populations. Many modern Europeans and Asians today have about 2 per cent of Neanderthal DNAs in their genomes.

Intriguingly, snippets of Neanderthal DNA pop up more frequently in modern humans than others. Scientists have been wondering whether these frequently appearing Neanderthal DNAs confer some functional benefits to modern humans.

Recent studies from Stanford University, USA, have compelling evidence that these frequent snippets of Neanderthal DNAs have major functional benefits for the modern humans. Neanderthal genes offered defence ability to modern humans.

When modern humans started migrating from Africa and reached Eurasia they encountered the Neanderthals, who had been inhabiting those lands for hundreds of years and had evolved a defence mechanism against many viruses that were not present in Africa. The absence of these viruses in Africa deterred humans from developing the viral defence ability.

It was much easier on part of the modern humans to borrow the viral defence mechanism from the Neanderthals than waiting for long to evolve their own defence mechanism. These became possible through genetic mix ups as a result of frequent interbreeding between modern humans and the Neanderthals.

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“Our research shows that a substantial number of frequently occurring Neanderthal DNA snippets were adaptive for a very cool reason,” said Dmitri Petrov, the lead scientist of the study in Stanford University, adding, “Neanderthal genes likely gave us some protection against viruses that our ancestors encountered when they left Africa.”

The findings are consistent with the poison-antidote model of gene swapping between two species. In this way, Neanderthals transmitted to modern humans not only infectious viruses but also the mechanism to combat them.

Modern humans and the Neanderthals are so closely related that the viruses jumping from one to the other did not witness a genetic barrier of any sort. It is only due to this closeness that Neanderthals could pass on the genetic basis of the defences against those viruses to us.

Also Read: Genetic Variations in Neanderthals can Explain Human Brain Evolution

The scientists, in their study, compiled more than 4,500 genes in modern humans that are known to interact in some way with viruses. They then checked these genes with an existing database of Neanderthal DNA and could identify 152 DNA fragments from modern humans to be present in Neanderthals as well.

They also found that the 152 genes that we inherited from our early ancestors interact in the immunogenic fight against modern day HIV, influenza A and Hepatitis C. Interestingly, all these viruses are the RNA virus—those viruses which have RNA as their genetic material. They concluded that these inherited genes could help the modern humans to fight the RNA viruses that they encountered upon leaving Africa.

An interesting aspect of the study is that the genes they identified are present in modern European populations, suggesting that different viruses would have influenced gene swapping between Neanderthals and the ancient ancestors of today’s Asians. This is also expected, because interbreeding between modern humans and Neanderthals is thought to have occurred in multiple locations and multiple times. These happenings throughout prehistory would have encountered different viruses.