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Polar bears, brown bears interbred during warm periods. Is it happening again? (+video)

Polar and brown bears diverged between 4 million and 5 million years ago, but they continued to interbreed when the climate warmed, finds a new study led by the University at Buffalo and Penn State. Now, there is evidence that it is happening again.

National Geographic Explorer Beth Shapiro describes the common ancestry of polar bears and brown bears.
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Polar bears' past may echo their future, indicates a genetic study that finds the white-furred, sea ice-dwelling bears interbred with brown bears long after the two species separated as much as 5 million years ago.

Climate change likely drove this mixing among bears, writes the research team, noting there is evidence this is happening again.   

"Maybe we're seeing a hint that in really warm times, polar bears changed their lifestyle and came into contact, and indeed interbred, with brown bears," said study researcher Stephan Schuster, a professor of biochemistry and molecular biology at Pennsylvania State University, and a research scientist at Nanyang Technological University in Singapore, in a statement.

The study estimates polar bears split from brown bears between 4 million and 5 million years ago, after which they endured fluctuations in climate, including ice ages and warmer times. 

Polar bears are currently facing the effects of climate change, this time caused by humans, as the Arctic sea ice upon which they live recedes to unprecedented levels.

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