Polar Bear Ancestry Goes Back 600,000 Years, Four Times Longer Than Previously Thought

Polar bears evolved more than half a million years ago, new research shows, indicating they may have more trouble adapting to climate change than previously thought

Polar bears, thought to be at least 150,000 years old as a species, have ancestry going back at least four times that long, a recent study has revealed.

Analyzing a different type of DNA than has been used in the past, scientists in Germany found that polar bears may indeed have interbred with brown bears about 150,000 years ago, as a study in July 2011 noted. Mitochondrial DNA, passed down through the mother, linked the two bear species and led scientists to think that they had separated back then. But the new analysis in the journal Science, this time of nuclear DNA—which comes from both parents—suggests that they were more likely meeting up than diverging.

Researcher Frank Hailer of the Senckenberg Nature Research Society in Frankfurt told LiveScience.com that the polar bear age question had nagged at him because he didn’t think that 150,000 years was enough time for the bear to develop the adaptations needed to survive in an Arctic climate. What he and a research team found in the latest analysis makes more sense, Hailer told LiveScience.

"We found that polar bears are much older than we previously knew from other studies; their appearance dated to about 600,000 years ago," Hailer said. "That would make sense around that time for something like a polar bear to evolve, because Arctic habitats were much larger than they are today, so there would have been much larger habitats that would have been suitable for a species like a polar bear.”

The polar bear has become emblematic of climate change as the animals’ icy habitat melts, forcing them to swim farther and farther between diminishing ice floes and endangering the survival of cubs, which are not strong enough to swim the longer distances. A study released last year by the World Wildlife Fund and other groups found a 45 percent mortality rate among polar bear cubs forced to swim long distances for food and habitat, as opposed to 18 percent mortality for those in normal swims, Reuters reported in July 2011.

This makes the new findings sobering, given that polar bears may adapt much slower to changing conditions than was previously thought, the researchers said. On the one hand, the findings in the paper published on April 19 in the journal Science indicates that polar bears have adapted to warming climate before. On the other hand, previous climate warming has been more gradual, without humans helping it along, so it is not clear if polar bears can adapt at the faster pace.

Inuit peoples have been sounding the alarm on polar bears and climate change for years, and Canada has declared the animal a "species of special concern." Climate change may even be responsible for cannibalism among polar bears, according to some reports.

The 600,000 years is the most likely date of species divergence out of a possible range of 338,000 to 934,000 years ago, Hailer said, according to The Independent.

"It was the first dramatic cooling period of the ice ages,” Hailer said of the date 600,000 years ago. “Our data on the polar bear lineage may be coincidental but it fits in with the time period when the climate was very cold.”

Hybrids of polar and other types of bears have been discovered over the past several years, suggesting that the trend is occurring again, this time as a result of climate change, according to The Independent.