Woolly mammoths done in by climate

June 8, 2007

Courtesy of  Far North Science
By Doug O'Harra

Woolly Mammoth
Credit: Wikipedia Commons

The last of the mammoths disappeared from the Far North about 10,000 years ago. Sorting out the causes of mammoth extinctions, along with the disappearance of a menagerie of other fabulous ice-age mammals - has long been one of paleontology's hottest controversies.

Were they wiped out by human hunters that trudges out of Siberia and crossed the Bering Land Bridge? Or did a slow shift in climate alter what Dale Guthrie at the Univesity of Alaska Fairbanks has called "the mammoth steppe," leaving them with less to eat and soggier ground?

An international team of seven scientists have uncovered new clues to what they're calling "a very cold case," the demise of woolly mammoths from the Far North. And the study found evidence that ancient climate and genetic shifts undercut mammoth survival, possibly taking humans off the hook for the ice-age kill-off.

In an article appearing June 7 in Current Biology, a publication of Cell Press, the scientists report that mammoths substantially expanded their range during the last interglacial period, creating two different populations, and setting the stage for later extinctions.

Scientists have long debated what wiped out more than 40 large mammal species across North America over a few thousand years at the end of the ice age. One theory maintains that humans migrated across the 1,000-mile-wide Bering Land Bridge from Asia as glaciers retreated and hunted down critters like mammoths and ancient bison during their sweep across the continent.

In that idea, people triggered a wave of extinctions up and down the food chain.

But the rise of sophisticated DNA analysis for fossils has led to much more sophisticated understanding. Over the past 10 years, scientists have discovered suggestions of complex genetic and environmental factors in the demise of the mammals.

More details from a story about the current mammoth research:

DNA lifted from the bones, teeth, and tusks of the extinct mammoths revealed a "genetic signature" of a range expansion after the last interglacial period. After the mammoths' migration, the population apparently leveled off, and one of two lineages died out.

"In combination with the results on other species, a picture is emerging of extinction not as a sudden event at the end of the last ice age, but as a piecemeal process over tens of thousands of years involving progressive loss of genetic diversity," said Dr. Ian Barnes, of Royal Holloway, University of London.

"For the mammoth, this seems much more likely to have been driven by environmental rather than human causes, even if humans might have been responsible for killing off the small, terminal populations that were left."

The new research comes after Barnes, (with Adrian Lister of the University College London and the Natural History Museum in London and Guthrie at UAF, and others) had earlier found evidence that bison, bears, and lions underwent major population shifts some 25,000 to 50,000 years ago. That's before glaciers reached their maximum extent about 20,000 years ago, and many thousands of years before the ice retreated and humans expanded in number.

As a story on the report says, "the findings . offered early human hunters a potential alibi."

The genetic analysis showed that mammoths had separated into two different groups, and one of the groups died out about 40,000 years ago. The authors say there's a lesson for the present.

"At a time when we should be very concerned about the potential extinction of many existing large mammals, studying those that occurred in the geologically recent past can provide many insights," Lister said in a release.

"Our work, together with that of others, shows that the conditions for extinction can be set up long before the actual extinction event."