KELLY MCEVERS, HOST:
If you have ever seen what Neanderthals were thought to look like, it's hard to believe modern humans would find them in any way appealing. But humans actually did mate with them. A few years back, scientists found Neanderthal DNA in modern humans. And NPR's Christopher Joyce reports on some new evidence that suggests what affect that DNA might have had.
CHRISTOPHER JOYCE, BYLINE: If you look at a Neanderthal skeleton next to a modern human skeleton, the Neanderthal looks stocky, barrel-chested and rather brutish. They lived in Europe and Western Asia. Modern humans lived in Africa. But about 60,000 years ago, those modern humans got restless and traveled to Eurasia. They met the Neanderthals and, apparently, some liked what they saw. They had kids. Those kids got genes from both groups. Some of those genes got passed on down to the present. And now, Tony Capra has found some intriguing Neanderthal genes in modern Americans.
TONY CAPRA: For example, we found specific bit of Neanderthal DNA that was associated with increased amounts of blood clotting.
JOYCE: Capra's at Vanderbilt University. He compared DNA from Neanderthal fossils to DNA from 28,000 Americans in the medical database. Writing in the journal "Science," Capra says his colleagues also found Neanderthal DNA that's associated with things like keratosis, growths on the skin. Another association - depression. But he notes these are just associations. There's no evidence that DNA is the direct cause of these conditions.
CAPRA: This Neanderthal DNA influences this general bodily system in humans. But it doesn't mean that it was bad for us or bad for them.
JOYCE: Many medical conditions are influenced by numerous genes. Having one piece of Neanderthal in the mix isn't likely to have much effect. But Capra says it could be that some Neanderthal genes stuck with us because at some point, they helped us adapt as we spread across the planet. For example, the Neanderthal version of blood clotting DNA may show up more often than expected because blood clotting helps fight infection. It could be that the Neanderthal version worked better on the bacteria found in Eurasia. So whoever had that version had a better chance of surviving and passing the gene on. Geneticist Ken Weiss of Penn State University says the closer scientists look for these bits of shared DNA, the more they'll find.
KEN WEISS: It's interesting but just not a surprise anymore.
JOYCE: Weiss says it's not that different from the way people exchange genes now.
WEISS: You're going to find evidence of things in Mexican-Americans that came from Europe or came from Native Americans.
JOYCE: In a way, our species evolved much the way languages do, made up of bits and pieces of whoever we met and lived with along the way. Christopher Joyce, NPR News.
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