It's possible that somewhere on the internet you'll find someone who is having a tough time accepting the evidence that our forebears, after making their way out of Africa, interbred with Neanderthals, a species of ancient human already living in Europe at the time. Might it be difficult for these naysayers to accept that our ancestors mated with a losing species — one that perhaps died out in the face of our excellence? Who knows. But the current scientific understanding of the matter is, the ghost of the Neanderthal genome is present in our DNA: Most modern humans of European and Asian descent carry around about 2 percent Neanderthal material.
Neanderthals had a long time on this planet to evolve — the most conservative estimates puts them traveling north out of Africa 350,000 years ago, but it could easily be almost twice that long ago. Modern humans only made our break for the northlands around 45,000 years ago. Five thousand years later, the Neanderthals appeared to have disappeared from Europe, but new evidence suggests they left some important DNA behind.
A study published online on Oct. 4, 2018 in the journal Cell finds that some of the genetic material we retained from our ancestors' trysts with Neanderthals has served us well over the millenia. Because Neanderthals had been in Europe and Asia for so much longer than we had when we met them, interbreeding likely provided a shortcut to the long process of adapting our own genetic resistance to common viruses in this new land — they had, after all, been building their genetic defenses for hundreds of thousands of years.
"Modern humans and Neanderthals are so closely related that it really wasn't much of a genetic barrier for these viruses to jump," said coauthor David Enard, an assistant professor at the University of Arizona, in a press release. "But that closeness also meant that Neanderthals could pass on protections against those viruses to us."
The research team combed the human genome for every gene responsible for providing us with defenses against viruses — about 4,500 individual genes in all — and then compared what they found to the Neanderthal genome. Over 150 fragments of modern virus-busting genes were also present in Neanderthals. These genes participate in our immune response to RNA viruses like HIV, influenza A and hepatitis C.
This research is unique in that it's the first time scientists have proved it's possible to sort through an ancient species' genome for evidence of disease.
"It's similar to paleontology," said Enard. "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."