Newspaper article International New York Times

Bison DNA Pinpoints Migration to America

Newspaper article International New York Times

Bison DNA Pinpoints Migration to America

Article excerpt

Two groups of experts generally agree that a gateway from Siberia to North America opened about 13,000 years ago, but not on who used it first.

Two teams of scientists have succeeded in dating the opening of the gateway to America, only to disagree over whether the Clovis people -- one of the first groups from Siberia to reach the Americas -- ever used the gateway to gain access to the New World.

About 23,000 years ago, in a period of intense cold that preceded the end of the last ice age, glaciers from west and east merged to cut off Alaska from North America. With so much of the world's water locked up in ice, sea levels were much lower and a now-lost continent, Beringia, stretched across what is now the Bering Strait to join Siberia to Alaska. But people who had trekked across Beringia to Alaska could go no further because of the ring of glaciers that blocked their way south.

Ten thousand years later, the glaciers started to retreat and an ice-free corridor, roughly 900 miles long, opened between Alaska and the Americas. In the middle of the corridor lay a body of water, 6,000 square miles in area, fed by the melting glaciers and known as Glacial Lake Peace. Not until the lake had drained away, and plants and animals had recolonized the corridor, would early peoples have been able to support themselves as they traversed the corridor between the glaciers.

Using new methods for analyzing ancient DNA, the two teams of scientists have each developed ingenious ways to calculate the date at which the corridor first became fit for human travel. A group led by Peter D. Heintzman and Beth Shapiro of the University of California, Santa Cruz, regards bison as the ideal proxy for assessing human travel through the corridor, given that bison were a major prey of early hunters.

When the glaciers merged 23,000 years ago, the bison populations in Alaska and North America were separated and started to evolve minor variations in their mitochondrial DNA, a genetic element that survives well in ancient bones. Dr. Shapiro's team collected ancient bison bones from up and down the corridor, analyzed their mitochondrial DNA and looked for Alaskan bison that had traveled south through the corridor and American bison that had traveled north.

The corridor was "fully open" for bison traffic about 13,000 years ago, Dr. Shapiro and colleagues reported on June 6 in the Proceedings of the National Academy of Science, and human populations could have traversed it at the same early date. "Our chronology supports a habitable and traversable corridor by at least 13,000" years ago, "just before the first appearance of Clovis technology in interior North America," they write.

The Clovis culture was long thought to belong to the first people to reach the Americas. But archaeologists have now detected human presence in the Americas as early as 14,700 years ago. …

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