Mysterious Bear Extinctions
A study led by Alan Cooper of England's University of Oxford used the genetic records of brown bears from BeringiaSiberia and North America and the connected by a land bridge that existed until 11,000 years agoto determine the effects of climate change on different bear populations.
Cooper's team analyzed genetic changes in 36 brown bear bones, some excavated on field expeditions and others gathered from collections in New York's American Museum of Natural History and the Canadian Museum of Nature in Ottawa.
"If we look at animals today, we see many sub-species, but this doesn't tell us how long these various groups have been around or how long previous groups, now extinct, lasted," said evolutionary biologist Adrian Lister of University College in London.
But with the new DNA evidence, "they are looking directly back into the past and can actually see the movements of different populations," Lister explained.
The analysis revealed "quite a bizarre population history" of the brown bear, said molecular paleontologist Ian Barnes of the University of Oxford, who conducted much of the study.
Insight Into Origin of New Species
The ancient distribution of bears was quite different from now. A type of brown bear that was common near Fairbanks, Alaska, became extinct about 35,000 years ago. "There are no modern bears with these genetic characteristics," said Barnes. The team found no record of brown bears in Beringia between 35,000 and 21,000 years ago.
What is most surprising to Barnes is that the population trends don't seem to correlate with climatic conditions. The last ice age lasted from approximately 90,000 to 10,000 years ago, although there was a slight warming between 35,000 and 21,000 years ago.
"If anything," said Barnes, "we would have predicted an extinction between 21,000 and 16,000 years ago," when the size and thickness of the glacier covering most of Canada and some of the northern United States peaked and when food may have been most scarce.
But the extinction of the Fairbanks bear about 35,000 years ago strikes Barnes as odd, as this suggests a warmer period.
Equally surprising, said Barnes, is the reappearance of brown bears about 21,000 years ago, and the appearance of a new, genetically distinct group of bears near Fairbanks that still exist today.
One explanation is that the mysterious disappearance of the brown bear may not have been the result of climate change but of a fearsome competitorthe three-meter-tall, carnivorous short-faced bearwhich seems to have dominated the region during that period. When the short-faced bear became extinct in Alaska and Canada about 21,000 years ago, the brown bears seemed to reappear and fill that niche.
Lister said Barnes' study "helps us understand the origin of new species" by revealing the genetic and geographical history of brown bears over the last 60,000 years.
Both Lambert and Barnes hope to probe the inhospitable icy reaches of the planet for more hidden genetic treasures that could hold the secrets of life past.
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