New evidence suggests that precursors to modern polar bears first appeared about four or five million years ago, making the beginning of the evolutionary split much earlier than previously thought. The polar bear's ancestors diverged from brown bears and underwent a series of evolutionary changes in order to survive in the harsh conditions of the Arctic—adapting to a life of hunting seals and surviving extreme cold.

Interestingly, the genome evidence shows that after brown bears and polar bears separated, there were periods when they came into contact again. The new study also reveals surprisingly little genetic diversity in today's polar bears, suggesting bottleneck periods, probably during warm periods, when their numbers were severely reduced.

What does this mean in the face of the current arctic warming now taking place?

  • First, the longer evolutionary period shows that polar bears won't be able to adapt to changing sea ice conditions within a mere one hundred years.
  • Second, although the longer time frame means that polar bears survived previous warm periods, the temperatures reached in the Arctic if we continue on our present greenhouse-gas-warming course will be unlike anything polar bears have survived before.