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Comments in the journal Science for July 10, 2009, have questioned the results reported here, but in the same issue, the original researchers reply to the criticisms and stand by their conclusions.


University of Oregon archaeologist Dennis Jenkins holds a human coprolite found at Paisley Caves. (Andrew Curry)

The remarkable discovery of 14,300-year-old feces in eastern Oregon's Paisley Cave provided the earliest direct evidence of human colonization of the Americas. Known in the laboratory as coprolites, the feces were proof positive that humans lived in North America well before the Clovis people, long thought to have been the first arrivals, around 12,000 years ago. Thanks to a new technique for isolating genetic samples from materials such as ice, soil, and now fecal matter, researchers were able to extract human DNA from the coprolites. The improbable "artifacts" opened a new chapter in the debate over the identity of the first Americans.

But Paisley Cave wasn't the only source of genetic evidence reshaping ideas about how and when the Americas were settled. A multinational team of geneticists completed the most comprehensive study yet of Native American mitochondrial DNA (the genetic material contained within the organelles that provide human cells with energy). By looking at variations in the DNA between different modern-day Native Americans, the researchers determined that the first people probably arrived about 18,500 years ago. "It looks like there was a migration out of Asia into Beringia and there was a stopover for a few dozen generations," says geneticist Scott Woodward of the Sorenson Molecular Genealogy Foundation. "Then these people spread quite rapidly into the Americas." But not so rapidly that they couldn't take a pit stop in a cave in eastern Oregon.

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