*** To explain the findings, the researchers proposed a strange scenario: The brown bears of ABC Islands were once polar bears. But as the glaciers melted thousands of years ago, those polar bears became trapped on their islands.
Further warming led to better conditions for brown bears to colonize the Alaskan mainland. Because males are the ones that disperse, they swam across the channel to the ABC Islands over a long period of time, mating with the local females (polar bears). As a result, the ABC bears eventually came to look and act like brown bears, while still maintaining traces of their polar bear past in their mitochondrial DNA.
The genetic analysis revealed a wide estimate for when brown bears and polar bears first diverged, ranging from hundreds of thousands to millions of years ago.
The findings suggest people should ignore ABC bears when trying to sort out polar bears' history, Shapiro said.
Unfortunately, scientists aren't any closer to solving the mystery of polar bear origins.
"Polar bears live in a place that it is very unlikely that they're going to leave fossils," Shapiro said, referring to the fact that fossils don't survive in the icy, watery conditions of the Arctic. That makes it difficult to trace their evolution from a common ancestor with brown bears, she said...
