Study Suggests Modern Humans Inherited Neanderthals’ Viral Defenses

Neanderthals' viral defenses
UNiesert/Frank Vincentz (montage: Abuk SABUK) [GFDL or CC BY-SA 3.0], via Wikimedia Commons
Scientists have long believed Neanderthals are extinct species of earlier humans. However, scientists say that before mysteriously vanishing from our planet, they bred with another human species, which caused modern humans to inherit 2% of their DNA, including Neanderthals’ viral defenses.

Now they have found that some parts of Neanderthal DNA appear in modern humans, including Europeans and Asians. Scientists have been wondering if this 2% of Neanderthal DNA offered some genetic advantage to modern humans, and now researchers from the University of Stanford say modern humans may have inherited Neanderthals’ viral defenses.

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

Scientists say that when the first contact between ancient humans and Neanderthals occurred, one group had already been living outside Africa for hundreds of thousands of years. That meant they were already used to the terrain and climate of other continents, which allowed them to develop defenses against viruses present in Europe and Asia. However, our ancestors from Africa would have been much more vulnerable to these infections.

“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, a former postdoctoral fellow at Petrov’s lab who is now an assistant professor at the University of Arizona. “Modern humans and Neanderthals are so closely related that it really wasn’t much of a genetic barrier for these viruses to jump. But that closeness also meant that Neanderthals could pass on protections against those viruses to us.”

Their study was published on Oct. 4 in the journal Cell, and it suggests that the Neanderthals’ viral defenses which were passed on to modern humans were against RNA viruses. The viral defense binds with genes from RNA, which is similar to DNA.

To come to this conclusion, the team analyzed a list of more than 4,500 genes in modern humans which are known to interact with some viruses. After that, Enard checked the list against a database containing Neanderthal genes that had been sequenced. They managed to identify 152 fragments of genes that are now found in modern humans but also had belonged to Neanderthals.

The 152 genes they say were inherited from Neanderthals interact with modern-day viruses like HIV, influenza A, hepatitis C and all types of RNA viruses. Based on their findings, the team concluded that our ancestors received these genes by interbreeding with Neanderthals. That enabled them to fight infections that were common in Europe and Asia using the Neanderthals’ viral defenses.

“It’s similar to paleontology,” Enard added. “You can find hints of dinosaurs in different ways. Sometimes you’ll discover actual bones, but sometimes you find only footprints in fossilized mud. Our method is similarly indirect: Because we know which genes interact with which viruses, we can infer the types of viruses responsible for ancient disease outbreaks.”