Polar bears might have originated about 600,000 years ago, an international team reports April 20 in Science.
Previously, studies suggested that the polar bear, Ursus maritimus, emerged much later, about 150,000 years back. But many of these estimates were based on analyzing limited genetic information that’s passed down only through the maternal bloodline called mitochondrial DNA.
In the new study, researchers partially decoded DNA inherited from both parents from 45 bears, including polar, brown and black bears. Called nuclear DNA, this type of DNA carries the majority of an organism’s genetic instructions. A comparison of the various species’ nuclear DNA indicates that polar bears are much older than previously thought. This means that populations likely survived through several glacial periods and the warmer times between.
But the polar bear population’s lack of genetic variation suggests that the warm phases created a genetic bottleneck, wiping out many individual bears. Study coauthor Frank Hailer of the Biodiversity and Climate Research Centre in Frankfurt says that adding climate change, speeded up by humans, to stresses such as habitat loss, pollution and hunting might pose a threat to polar bear survival.