According to a study in the journal Current Biology, every polar bear alive today can trace its ancestry to one mama bear that lived in Ireland during the last Ice Age. And what's more, she wasn't even a polar bear: She was a brown bear. An associate professor of biology at Penn State University said that her team studied DNA extracted from ancient bear bones.
When the team looked at the nuclear DNA, they found that brown bears and polar bears began to evolve separately from each other around a million years ago. But the mitochondrial DNA, the kind you inherit from your mother, told a very different story. They diverged only about 20- or 30,000 years ago. And that difference is intriguing, and it means there's something weird going on in the history of polar bears.
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