Planet Earth

32. Tooth DNA Dates The First Americans

By Anne CasselmanDec 28, 2007 12:00 AM

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It’s probably the happiest root canal ever: Molecular archaeologists reported last January that they had drilled into a 10,300-year-old human tooth discovered in Alaska and extracted genetic gold. The molar, recovered from skeletal remains found in 1996 in On Your Knees Cave, located on Prince of Wales Island off southern Alaska, holds the oldest genetic sample ever recovered in the Americas. That sample supports the theory that humans first arrived here about 15,000 years ago and then migrated down the continent’s western coastline.

Brian Kemp, a molecular anthropologist at Washington State University who led the study, found that out of 3,500 Native Americans examined from a genetic database, 1.5 percent showed the same genetic pattern in their mitochondrial DNA as that found in the ancient tooth. “What’s interesting is that the distribution is almost entirely down the west coast of the Americas, all the way down to Tierra del Fuego,” says Kemp. That, says Theodore ­Schurr, an anthropologist at the University of Pennsylvania, “lends credence to the reemerging hypothesis that the first modern human populations to arrive in North America and then populate the rest of the Americas used a coastal route to actually get there.”

Kemp also compared the ancient DNA with its related modern DNA to see how fast it mutated over time. This “molecular clock” of mutation rates can be used to calculate when the ancestors of today’s Native Americans first arrived on these shores. Previous estimates pegged their appearance as far back as 40,000 years ago, but Kemp’s newly calibrated clock speeds up the scenario. “Within the last 15,000 years is my bet,” he says.

Go to the next story: 33. How to Erase a Single Memory

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