Modern Humans Inherited Virus Defenses From Interbreeding With Neanderthals

Modern humans and Neanderthals

Modern humans and Neanderthals

Modern humans have the ability to fight off infections like flu and hepatitis because of the Neanderthal DNA they inherited from their ancestors, new research has found.

Current thinking is that modern humans began moving out of Africa and into Eurasia about 70,000 years ago. This could have been deadly for the human species since Neanderthals encountered many infectious viruses while living for hundreds of thousands of years outside Africa.

"It made much more sense for modern humans to just borrow the already adapted genetic defenses from Neanderthals rather than waiting for their own adaptive mutations to develop, which would have taken much more time", said David Enard, an evolutionary biologist, now at the University of Arizona. Everyone in this world, apart from sub-Saharan populations, have up to 2% Neanderthal DNA as a result of this intimate encounter between the two species. It makes sense, according to researchers, as the interbreeding between humans and Neanderthals occurred at different times and in different places, thereby possibly involving different viruses each time they interbred.

The Neanderthal genes they identified are present only in modern Europeans, suggesting that different viruses influenced genetic swapping between Neanderthals and the ancient ancestors of today's Asians.

In 2016, while working at Stanford University with researcher Dmitri Petrov, Enard found roughly a third of all protein adaptations in the human genome were triggered by viral infections.

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The article with the conclusions published in the scientific journal Cell. The new work built on those findings looked at which of those adaptations may have come from Neanderthals. They reasoned that descendants of H. sapien-Neanderthal interbreeding events who carried Neanderthal genes for pathogen-fighting proteins would have been more likely to survive and pass the genes along. Then the researchers cross-referenced the list with the database of the DNA of Neanderthal and identified 152 total fragment.

However, the scientists know we got more genes from Neanderthals but, as the time passed by, those less useful genes were eliminated. Those sequences are publicly available to investigators in the field.

"Modern humans and Neanderthals are so closely related that it really wasn't much of a genetic barrier for these viruses to jump", said Enard, who is now an assistant professor at the University of Arizona in the US.

"Many Neanderthal sequences have been lost in modern humans, but some stayed and appear to have quickly increased to high frequencies at the time of contact, suggestive of their selective benefits at that time", Petrov said.

The study concluded that interbreeding between ancient humans and Neanderthals provided us the immunity against some ancient viral epidemics. "We trust that protection from particular RNA infections given by these Neanderthal groupings was likely a major piece of the objective behind their specific advantages". This could potentially inform better ways to monitor for and treat future epidemics.

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