The oldest known polar bear fossils hail from Svalbard and northern Norway and are dated at 115,000\u2013130,000 years old, before the beginning of the last\u00a0Ice Age.<\/p>\n
But some biologists think that polar bears diverged from brown bears as early as 600,000 years ago.<\/p>\n
According to research, polar bears evolved from brown bears that ventured onto the frozen ocean to stalk marine mammals during the last major period of glaciation.<\/p>\n
Through natural selection, the palest individuals with the greatest amount of fat would have had the best chance to survive and therefore reproduce.<\/p>\n
It was not a single, clean-cut departure, however, and repeated pairings between both species occurred (DNA analysis shows only a 1 per cent difference between polar bears and one Alaskan brown bear population).<\/p>\n
Shrinking sea-ice is forcing landlocked polar bears to mingle with their southern cousins once again, particularly as the latter are now travelling farther north.<\/p>\n
In coastal Arctic Alaska, grizzlies have been observed feasting on bowhead whale carcasses, sometimes in the company of polar bears, and interbreeding has been documented.<\/p>\n