RENEE MONTAGNE, HOST:
Scientists have been learning some remarkable things about the sexual history of humans by digging DNA out of fossil teeth and bones. For example, they found DNA from Neanderthals that is also found in modern humans. Apparently, our own ancestors mated with them. Now there's evidence that early humans may have bred with yet another extinct species, and as NPR's Christopher Joyce reports, it may have done us some good.
CHRISTOPHER JOYCE, BYLINE: Early humans apparently were not too picky about who they had sex with. Don't take my word for it. Here's geneticist Rasmus Nielsen from the University of California at Berkeley.
RASMUS NIELSEN: We exchanged genes with a lot of other lineages that existed 100,000 years ago - 50,000 years ago. We are, in some sense, mongrels.
JOYCE: One of those lineages was the Neanderthals, usually thought of as dull, brutish and very hairy. As a result, a lot of us have a little Neanderthal for DNA.
DAVID REICH: Whether didn't anything useful or important, biologically, today - that was another question.
JOYCE: That's geneticist David Reich at Harvard University. He says yes, some of those Neanderthal genes actually made us resistant to some pathogens and more susceptible to some diseases as well. So now comes the latest news. It wasn't just Neanderthals that mated with our ancestors and gave us something useful - apparently, says Rasmus Nielsen, we mated with the Denisovans. Yes, Denisovans - not from outer space, but another extinct human relative. Scientists know their DNA from finger and toe bones and a tooth found in the Denisova Cave in Siberia. Writing in the journal "Nature," Nielsen says he's found what appears to be Denisovan DNA in one group of modern humans - tibetans. And it's actually a gene that does something quite useful.
NIELSEN: There's a characteristic of Tibetans that they have gained so that they're able to live in high altitudes.
JOYCE: Altitudes like two and a half miles up - the ancient Denisovan gene protects against stroke and other ailments that can afflict people who live where oxygen is very thin. Geneticist David Reich suggests the gene could possibly have come from some other archaic human cousin. There seem to have been quite a variety of early humans around the time, but he adds that the important point is there's value in a species being, shall we say, liberal in its mating habits.
REICH: These genetic variations were opportunities to adapt to different environments - different flavors that allow people to respond differently to environmental challenges like altitude.
JOYCE: Though, it's doubtful that's what the first human-Denisovan couple was thinking at the time. Christopher Joyce, NPR News.
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