ROBERT SIEGEL, host:
It is the rare news story that features ancient spit. But you're about to hear one.
A team of scientists has found that it's possible to extract human DNA from the prehistoric saliva left in chewed up leaves. And by studying this DNA, the researchers hope to learn more about the first humans to settle in the American Southwest.
Here's NPR's Joe Palca.
JOE PALCA: Sometimes, a moment of scientific insight is unforgettable. Etched in a scientist brain - sometimes.
Dr. STEVEN LeBLANC (Director of Collections, Peabody Museum of Archaeology and Ethnology, Harvard University): I can't quite remember how I got the idea.
PALCA: Steven LeBlanc is director of collections at the Peabody Museum of Archaeology and Ethnology at Harvard University.
Dr. LeBLANC: I mean, I must have been in the museum somewhere and saw the artifacts and it just hit me that, whoa, this is something we could possibly do.
PALCA: The artifacts LeBlanc is talking about are called quids - that's the technical term for something you chew on and then spit out. What LeBlanc wanted to do was to extract DNA from the quids, DNA that came from cells in the chewer's saliva. Scientists have already successfully extracted DNA from ancient bones and teeth and used that genetic data to track how people moved around the world. But bone and teeth can be hard to come by. Quids, on the other hand, are plentiful. It seems about 2,000 years ago, chewing shredded yucca was all the rage.
Dr. LeBLANC: We're not really quite sure why people used to do this. But quids have been found like this everywhere from caves in Oregon to central Mexico, from central Texas to California. So it was a widespread behavior. Some people think it was sort of like chewing gum, it was just something to do, and other people think that it doesn't actually taste all that good and it might have been done for medicinal purposes.
PALCA: As long as the quid-spitting took place in a dry environment, the quid hardened, so picking one up today isn't icky.
Dr. LeBLANC: It's a little softer than a rock. It's sort of closer to a dried sponge, I would think would be a better way of describing it.
PALCA: So LeBlanc sent samples of these quids to molecular biology labs, asked them to look for human DNA, and sure enough, they found some.
Ripan Malhi is a molecular anthropologist from the University of Illinois at Urbana-Champaign. He says getting DNA from quids may solve a problem for anthropologists trying to learn how and when humans first arrived in North America
Dr. RIPAN MALHI (Molecular Anthropologist, University of Illinois): Many members of Native American communities believe that ancient remains - remains like skeletal remains or teeth - are sacred, and they should not be destroyed for scientific study.
PALCA: Malhi thinks fewer people will have problems with scientists destroying quids.
In this first study of DNA from quids, Steven LeBlanc was really just trying to prove that it could be done. But he says the DNA data they did collect support a much-debated theory that the first people to farm in the American southwest migrated here from the south. LeBlanc says it will take lots more quids to confirm that's what happened. And a lot of those quids have been sitting in museum storerooms for a century or more.
Dr. LeBLANC: We are always being asked why do we keep all this stuff, why would anybody bother to keep this little wad of yucca fibers for 100 years? And DNA hadn't even been discovered when these quids were first put on the shelf. And the reasons we keep things in museums is because we come up with new ways to use them, to address questions that we didn't even know existed when they were first collected. And I think this is just a wonderful example of why we have museums.
PALCA: Or looked at another way, there's another reason not to clean out the attic.
Joe Palca, NPR News, Washington.
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