ARTICLES MODERN

By HENRY FOUNTAIN : It’s common to think of the land bridge that existed from time to time across what is now the Bering Strait as a one-way affair. After all, the route through the area known as Beringia is thought to be how many animals and humans made their way out of Asia and into North America.
But there were no “Eastbound Only” signs. Some animals — the ancestors of the camel, for example — went the other way, from North America into Asia. And there is no reason that a species couldn’t go both ways, if the conditions were right.

That appears to be the case with the woolly mammoth, according to a major phylogenetic analysis of this ancient species.

Hendrik Poinar of McMaster University in Hamilton, Ontario, and colleagues looked at mitochondrial DNA from 160 mammoth samples from across Eurasia and North America, as a way of determining who was related to whom. They identified several groups, or clades — some endemic to Siberia and other parts of Asia and others to North America, having been separated after mammoths first migrated eastward more than a million and a half years ago.

But as they report in Current Biology, the researchers found that at some point in the past 150,000 years, North American mammoths migrated back to Siberia. “When they’re coming back in, the endemic Siberian populations start to crash,” Dr. Poinar said, and by about 40,000 years ago the North American mammoths had completely taken over.

Whether the Siberian mammoths died out on their own (because of what is called genetic drift) or were outcompeted and otherwise outfoxed by their North American relatives isn’t known, though Dr. Poinar suspects it isn’t coincidental that the Siberian animals began to die out when the North American animals started arriving.

But either way, the mammoths that finally became extinct about 10,000 years ago were not of Siberian lineage. “I’m not sure the Russians would be happy that their iconic wooly mammoth has North American origins,” Dr. Poinar said.
MOMEEN reporting from HENRY FOUNTAIN