Sexual encounters between Neanderthals and ancient humans skewed in one direction—mostly between male Neanderthals and female humans.
Scientists have long known that Homo sapiens interbred with Neanderthals, who thrived across Europe and western Asia between about 400,000 and 40,000 years ago before going extinct. Now, new research reveals that these matings had a strong pair-up pattern.
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“It’s a really interesting, provocative hypothesis that there was this long-term mating preference,” said Joshua Akey, a Princeton University geneticist who wasn’t involved in the work.
DNA extracted from ancient bones and teeth has previously shown the genes from our extinct cousins live on in many present-day humans. Those genes play a role in our sleeping habits and our susceptibility to certain diseases, including Covid.
A trio of University of Pennsylvania researchers dug deeper into these ancient pairings and published their findings Thursday in a newstudy in the journal Science.
They compared DNA from 73 modern women in Africa to genetic information from three female Neanderthals. The group found the Neanderthals’ X chromosomes had 62% more modern human DNA than the rest of their chromosomes.
This reveals a pattern in ancient sexual pairings, said Alexander Platt, an evolutionary geneticist at the University of Pennsylvania and study co-author.
A male—who has an X and a Y chromosome—can pass on only one copy of the X chromosome, compared with a female with two X chromosomes.
If modern human females and Neanderthal males mated more, that means fewer X chromosomes from Neanderthals entered the human gene pool—and more X chromosomes from modern humans got passed onto Neanderthals, said Daniel Harris, another study co-author.
The two species likely mingled in several waves of interbreeding: one about 250,000 years ago and another about 45,000 years ago, according to Platt. The mating preferences his group noted remained consistent.
For Akey, the work demonstrates the power of ancient DNA as a research tool.
“Using genome sequences to be able to infer something about the social dynamics of interactions that happened tens or hundreds of thousands of years ago is pretty amazing,” he said.
Write to Aylin Woodward at aylin.woodward@wsj.com
