Nature Study Addresses Causes of Ice Age Extinctions

Did climate change or humans cause the extinctions of the large-bodied Ice Age mammals (commonly called megafauna) such as the woolly rhinoceros and woolly mammoth? Scientists have for years debated the reasons behind the Ice Age mass extinctions, which caused the loss of a third of the large mammals in Eurasia and two-thirds of the large mammals in North America, and now, an inter-disciplinary team from more than 40 universities around the world led by Professor Eske Willerslev and his group from the Centre for GeoGenetics, University of Copenhagen, has tried to answer the contentious question in one of the biggest studies of its kind ever. The study by the team, which includes two Texas A&M University professors, is published online on November 2, 2011 in the journal Nature and reveals dramatically different responses of Ice Age species to climate change and human impact. Using ancient DNA, species distribution models, and the human fossil record, the findings indicate that neither climate nor humans alone can account for the Ice Age mass extinctions. "Our findings put a final end to the single-cause theories of these extinctions," says Dr. Willserslev. "Our data suggest care should be taken in making generalizations regarding past and present species extinctions; the relative impacts of climate change and human encroachment on species extinctions really depend on which species we're looking at." The study reports that climate alone caused extinctions of woolly rhinoceros and musk ox in Eurasia, but a combination of climate and humans played a part in the loss of bison in Siberia and of wild horse. While the reindeer remain relatively unaffected by any of these factors, the reasons behind causes of the extinction of the mammoth remain unresolved.
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