Warmer climes and a shrinking population could force inter-species breeding.

Hansruedi Weyrich

It’s been a rough half-million years for the polar bear, so it sure doesn’t help that man-made climate change is driving them toward extinction.

According to a model published recently in PNAS, polar bears prospered during cool periods but struggled during warm ones, and their numbers have been declining since an exceptionally balmy period starting 420,000 years ago. That’s bad news (bears) with climate change now melting Arctic ice at unprecedented rates.

As polar bears become rarer, they may also be forced to mate with brown bears, which this new study suggests has happened before in the distant past. Modern polar and brown bears can and do produce fertile offspring, but biologists classify them separate species because geographical distance usually prevents the two from ever meeting. In zoos that keep bears in the same enclosure, distance is not a problem. A handful of hybrid polar-grizzly bears (grizzlies are a subspecies of brown bears) have been born in zoos in the Czech Republic, Germany, Israel, Poland, Russia, and Spain, according to the BBC.

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