DNA Evidence Weighs In on Ice Age Extinction Debate
Sarah Graham

The end of the Pleistocene epoch brought with it widespread extinctions of
large mammals, such as saber-toothed cats and mammoths. Ancient bison, too,
were threatened with elimination, but they managed to survive. The two
leading theories of what caused the precipitous population drop focus on
environmental shifts and pressure from human hunters. A genetic analysis
published in the current issue of the journal Science lends support to the
hypothesis that climate change was the culprit.

Beth Shapiro of Oxford University and her colleagues analyzed mitochondrial
DNA from 352 bison fossils recovered from eastern and western Beringia (the
landmass that includes Alaska, Canada and Siberia), North America, China and
Russia. In addition, the scientists performed radiocarbon dating on 220 of
the samples. They determined that the genetic diversity of the bison
population dropped off drastically around 37,000 years ago. "The timing of
this decline correlates with environmental changes associated with the onset
of the last glacial cycle," the team reports, "whereas archaeological
evidence does not support the presence of large populations of humans in
eastern Beringia until more than 15,000 years later."

Full Text at Scientific American
http://cl.exct.net/?fe6815727761047e7310-fe3016707360067c711779

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