Mammoth mystery solved

Los Angeles Times
Posted June 9 2007


Paleontologists long have assumed that massive hunting by humans led to the extinction of the woolly mammoths about 12,000 years ago, but new genetic analysis indicates that inbreeding and loss of genetic variability was the actual cause.

Paleontologists Ian Barnes of the University of London, Adrian Lister of University College London and their colleagues studied mitochondrial DNA samples from 96 bone, tooth and ivory specimens collected primarily in Alaska and Siberia. Their findings, published Thursday in the journal Current Biology, chart the animals' evolutionary history.

The animals apparently originated in Asia about 150,000 years ago, migrating over the land bridge connecting Siberia to Alaska in what is now the Bering Strait to form populations on two continents.

A gradual warming of the Earth caused sea levels to rise, inundating the bridge and isolating the two groups, which became genetically distinct.

About 100,000 years ago, the land bridge opened again, allowing the two groups to intermingle. By about 43,000 years ago, the Siberian lineage had died out, leaving only the Alaskan contingent.

The ice age 20,000 years ago then stressed the population further, the researchers said, reducing their viability.

"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," Barnes said.

"For the mammoth, this seems much more likely to have been driven by environmental rather than human causes."