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And now we're going to hear about what scientists are learning about how we evolved. This story begins with the discovery of a pinkie bone in a cave. A team of scientists from the United States and Germany eventually figured out it must've come from a previously unknown population of ancient humans.

As NPR's Joe Palca reports, it's just the latest example of how modern genetic techniques are transforming anthropology.

JOE PALCA: The pinky bone in question is more than 30,000 years old. It was unearthed in 2008 from what's called the Denisova Cave.

DAVID REICH: The Denisova Cave is in southern Siberia in the Altai Mountains in Central Asia. This bone is the bone of a probably six to seven-year-old girl.

PALCA: David Reich is at Harvard Medical School in Boston. He and colleagues from the Max Planck Institute in Leipzig were able to extract DNA from the bone and sequence all three billion letters of DNA that made up this girl's genome.

This is the second ancient genome this team has unraveled. The first was the Neanderthal genome announced earlier this year.

Reich says this girl is from an extinct group of people he's calling the Denisovans, a group no one had ever described before.

REICH: It's a sister group to Neanderthals, which means that it's more closely related to Neanderthals on average than it is to modern humans.

PALCA: But there's something even more interesting about the Denisovans. As he reports in the journal Nature, their DNA showed they were more closely related to humans currently living in New Guinea than to people in Europe or Asia.

REICH: And what it means is that there was gene exchange between relatives of this Denisovan and the ancestors of New Guineans.

PALCA: In other words, as they left Africa, modern humans must have passed through the realm of the Denisovans and had sex with some of the locals on their way to New Guinea. And if you look at a map, the route from Africa to New Guinea does not go through Siberia. So either the early humans from Africa took quite a detour, or there were Denisovans living over a quite a large swath of the globe. Right now, this pinky bone is the only known Denisovan fossil.

REICH: I think that their hunt should be on for more fossils and to understand the tools they used.

PALCA: So is it possible that there are bones in drawers in museums someplace that are Denisovans by this genetic signature, that people weren't really sure what they were in the past?

REICH: Ah-ha, yeah. Absolutely. And, in fact, this bone was labeled Modern Human in the drawer where it was assigned.

PALCA: It was only when Reich and his colleagues happened to examine its DNA that they found out what it really was. And this is the power of applying genetic sequencing techniques to ancient DNA.

JOHN HAWKS: It's so much more than we knew from the fossil record. It's really like discovering something for the first time.

PALCA: John Hawks is an anthropologist at the University of Wisconsin. He says genetic analysis will provide a much richer picture of life in the distant past. For example, a group in Spain published a paper this week analyzing the DNA from 12 Neanderthals found in a single cave. The analysis suggested the men were all brothers or cousins, whereas the women had all come from different families.

HAWKS: Looking at that one site, you've got this picture of the existence of a group and how they were related to each other. You know, how did they structure their groups? That's cool.

(SOUNDBITE OF LAUGHTER)

HAWKS: I mean, that's the kind of stuff that - it's something we have no access to in the archaeological record.

PALCA: It's stuff that can only come from sequencing ancient DNA.

Joe Palca, NPR News, Washington.

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