Mating with Neandertals reintroduced ‘lost’ DNA into modern humans

ORLANDO, Fla. — Interbreeding with Neandertals restored some genetic heirlooms that modern humans left behind in the ancient exodus from Africa, new research suggests.

Those heirlooms are versions of genes, or alleles, that were present in humans’ and Neandertals’ shared ancestors. Neandertals carried many of those old alleles, passing them along generation after generation, while developing their own versions of other genes. A small number of humans left Africa around 100,000 years ago and settled in Asia and Europe. These migrants “lost” the ancestral alleles.
But when the migrants or their descendants interbred with Neandertals, Eurasians reinherited the ancestral heirlooms along with Neandertal DNA, John “Tony” Capra reported October 20 at the annual meeting of the American Society of Human Genetics.

Present-day Europeans have more than 47,000 of these reintroduced ancestral alleles, and East Asians — who have more Neandertal ancestry than Europeans (SN Online: 2/12/15) — carry more than 56,000, said Capra, an evolutionary geneticist at Vanderbilt University in Nashville.

Capra and others have evidence that Neandertal versions of genes make humans more prone to some diseases (SN: 3/5/16, p. 18). Of the thousands of ancestral variants reintroduced into modern humans, only 41 have been linked in genetic studies to diseases, such as skin conditions and neurological and psychiatric disorders, he said. The researchers can’t tell for sure whether the effect is from the ancestral variant or neighboring Neandertal DNA. Capra and Vanderbilt colleague Corinne Simonti’s analyses indicate that the Neandertal DNA is more likely to blame. Many of the ancestral alleles are still present in modern-day Africans, Capra said, “so they’re unlikely to be very, very bad.”