Despite extensive genetic studies, the evolutionary relationship between polar bears and brown bears has been an ongoing debate. At the center of this controversy are brown bears from the Alaskan ABC Islands, in the Alexander Archipelago, which have mitochondrial DNA that looked just like polar bear DNA (mitochondrial DNA comes only from the mother). The authors of a recent study suggest that “the enigmatic ABC Islands brown bears derive from a population of polar bears likely stranded by the receding ice at the end of the last glacial period”. Alaska mainland was then colonized by brown bears due to climate warming. Brown bear males, which are the ones that disperse, would have swum across the sea to ABC Islands and mate with the female polar bears in the island over thousands of years. “As a result, the ABC bears eventually came to look and act like brown bears, while still maintaining traces of their polar bear past in their mitochondrial DNA” Science news report.
