DNA Evidence Confirms Humans and Neanderthals Mated

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Ever think that that friend of yours looks kind of like a caveman? Well, new research suggests you might be right.

A study led by Damian Labuda of the University of Montreal suggests that nine percent of modern-day humans may carry a bit of Neanderthal DNA on one of their sex chromosomes. “This confirms recent findings suggesting that the two populations interbred,” says Labuda, according to ScienceDaily. The fragment, found on the X chromosome, appears worldwide, except for among individuals from sub-Saharan Africa; this lends credence to the theory that Neanderthals and humans interbred between 50,000 and 80,000 years ago, after humans left Africa.

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“It’s in the Middle East, it’s in Europe, it’s in Eurasia, it’s in America, it’s in Australia,” Labuda told LiveScience. “This one event which led to this on the human X chromosome has to occur very early after modern man left Africa.” The research was published in the July issue of the journal Molecular Biology and Evolution.

Neanderthals, the most recent archaic humans, first appeared between 300,000 and 100,000 years ago and lived in Eurasia. These prototypical “cavemen” coexisted with modern humans for a time, before being replaced by them between 35,000 and 24,000 years ago.

In May 2010, scientists, led by ancient-DNA expert Svante Pääbo of Germany’s Max Planck Institute for Evolutionary Anthropology, reconstructed about 60% of the Neanderthal genome, using DNA of Neanderthal bones from Croatia. They found that a 1 to 4 percent overlap between the genomes of sample subjects from New Guinea, China, and France and that of the Neanderthal. They did not find the same correlations with DNA samples from southern and western Africa, suggesting again that the interbreeding occurred shortly after humans migrated from Africa. They also did not find any trace of human DNA in the Neanderthal genome, and the appearance of the Neanderthal DNA seemed to occur randomly indicating it does not confer evolutionary advantages.

Labuda had noticed a mysterious piece of DNA found on the X chromosomes of non-Africans about a decade ago. Armed with the 2010 sequence information, he studied 6,092 X chromosomes worldwide only to discover that his mysterious fragment indeed correlated with a fragment in the Neanderthal genome. Labuda’s next step is to ascertain whether this portion of DNA may have in fact provided  advantages to early modern humans as they struggled to survive.”It is interesting to know how many of these fragments there are, where they are, what they are doing,” Labuda said. “Are they neutral like the one which we have found, or do they provide some functional addition and could be maybe beneficial?”

Zara Kessler is a TIME contributor. Find her on Twitter at @zarafk. You can also continue the discussion on TIME‘s Facebook page and on Twitter at @TIME.