Ancient DNA evidence points to woolly mammoths' dynamic past

The largest study ever conducted of DNA evidence extracted from long-dead woolly mammoths points to a rockier past for the iconic Ice Age giants than many had suspected. The last mammoths left in Siberia some 50,000 to 5,000 years ago weren't natives, they report in the September 4th Current Biology, a Cell Press publication. Rather, they were North Americans that had migrated in and replaced the dwindling Siberian populations.

" The most surprising discovery was the North American origin for the last of the mammoths in Siberia," said Hendrik Poinar of McMaster University in Canada. "Something really happened to those Siberian guys. They literally fell off the face of the earth and were supplanted by North American mammoths. There was a lot of turnover going on—something that's difficult if not impossible to tell by looking at teeth, tusks and bones."

In the new study, the researchers analyzed mitochondrial DNA from 160 mammoth samples from across Holarctica (a region encompassing present day North America, Europe and Asia), representing most of radiocarbon time.

The study is the second largest to-date for any ancient DNA, said Poinar, noting that most previous studies of mammoths had focused on populations that lived on one continent or the other. Many had believed that the mammoths represented one big population connected by the roughly 1,000 mile long Bering Land Bridge that joined Alaska to eastern Siberia.

The new results provide a very different and more complex picture, he said. At one point, about 400,000 years, there might have been two distinct mammoth populations living together in Siberia. Those separate groups might even have represented different species of mammoth--the iconic woolly mammoth and another, more primitive form.

The evidence also suggests that, far from an open corridor, the Bering Land Bridge actually represented a significant barrier. "It's interesting that our data can be explained by just four or five migration events [across the Bering Land Bridge]," he said. "It was more of a filter than a freeway."

The results also refute the notion that climate change at the Last Glacial Maximum played a direct role in the mammoth's eventual demise.

" Populations declined much earlier in time, but then they responded well and 'sailed' through the Last Glacial Maximum with little effect on their overall diversity," Poinar said. "This puts the direct effects of climate change as a cause for extinction in question." Of course, indirect effects of the climate shift could still have played a role.

Based on the new findings, the researchers call for a revision of the classical view of mammoths' history. Rather than a simple "tale of two continents," they said, the new findings point to a much more dynamic pattern of mammoth evolution and extinction.

Source: Cell Press