Emily Chan
As recently as 70,000 years ago, polar bears developed key features to help them survive in extreme arctic conditions.
A team of molecular biologists from the University of Copenhagen in Denmark analyzed the genomes of three groups of bears—modern polar bears, modern brown bears, and fossilized remains of polar bears—to determine how they evolved to have certain adaptations, such as white fur and the ability to live off of a diet high in cholesterol.
Polar bears have two layers of fur to keep them warm and dry. The first is a large, downy undercoat, and the other is an overcoat made of longer hairs that act like a raincoat. Brown bears, on the other hand, only have one layer of fur.
Polar bears can also digest high amounts of cholesterol from meat containing a lot of blubber. They can thrive while eating seals and even some whale species like belugas. But if brown bears ate such a diet, they would develop heart disease and die at an early age.
Previous research has shown that polar bears are closely related to brown bears, but until now, it has not been clear when the two species diverged.
The scientists believe that polar bears and brown bears diverged within roughly the past one million years.
In the study, they compared the genomes of 119 modern polar bears, 135 modern brown bears, and two fossilized remains of polar bears to learn more about when they diverged from each other.
One of the fossilized polar bears helped the team pinpoint the divergence. The first fossil was a Poolepynten jawbone from the Norwegian archipelago of Svalbard.
It dates back between 130,000 and 100,000 years ago. The other fossil was the skull of a juvenile polar bear nicknamed Bruno.
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