German scientists who studied DNA samples from polar bears and brown bears say they have determined that polar bears did not descend from brown bears, as commonly assumed, but that the two species had a common ancestor about 600,000 years ago.
The findings challenge the idea that the bears adapted very quickly, but confirm that they have made it through warming periods and loss of sea ice before. It may have been touch-and-go for the bears, however, because the authors find evidence of evolutionary bottlenecks, probably during warm periods, when only small populations survived, even though warming was occurring much more slowly than it is now.
Read more from The New York Times: Investigating polar bear mysteries with a DNA lens
