"Robert Karl Stonjek"  wrote in
news:cp67us$2ud1$1{at}darwin.ediacara.org: 

> 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."

Without yet having read the article, my first question would be whether 
similar declines were noted in earlier ice ages and, if they were, whether 
the populations subsequently recovered or went on to extinction. My second 
question is how well the ultimate extinctions are dated. 

Yours,

Bill Morse
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