Genetic blueprints suggest the animals arose millions of years ago
The polar bear has been around for a surprisingly long time. A new analysis of its DNA suggests that Ursus maritimus split from the brown bear between 4 million and 5 million years ago — around the same time when, some scientists believe, the Arctic’s thick sea ice first formed.
With such old origins, the creature must have weathered extreme shifts in climate, researchers report online July 23 in the Proceedings of the National Academy of Sciences. Simulations of how the DNA changed over time suggest that polar bear populations rose and fell with the temperature. After thriving during cooler times between 800,000 and 600,000 years ago, the bears seem to have suffered a genetic bottleneck