10.3.2010 – Source: Canadian Press, Posted by Dave

March 01, 2010

Research that suggests polar bears have evolved more quickly than previously believed is creating new questions about their adaptability as they face a warming environment.

Scientists at Penn State University studied DNA from a rare fossil found in Norway and determined that polar bears developed only about 150,000 years ago — much more recently than the six million years some researchers previously thought.

It means that the bears survived the last interglacial period, a time that also saw warm temperatures in the Arctic.

“One of the messages that the general public needs to accept is just how dynamic and flexible species are and how fast groups of individuals adapt to selective pressure,” says Stephan Schuster, one of the lead authors of the report published Monday in the U.S.-based Proceedings of the National Academy of Science.

Polar bear fossils are exceedingly rare because the bears often die on the sea ice and their bodies eventually sink to the ocean floor.

But a well-preserved jawbone between 110,000 and 130,000 years old was found in Norway in 2004 — one of two such fossils in the world. Schuster’s group was able to sequence its DNA, making it the oldest mammalian genetic sequence in the world so far, and compare it to DNA from modern brown and polar bears.

“Our results confirm that the polar bear is an evolutionarily young species that split off from brown bears some 150,000 years ago and evolved extremely rapidly,” says report co-author Charlotte Lindqvist.

The results confirm that polar bears were around during the last interglacial period about 4,000 years ago — a time when the Arctic climate was generally warmer than now.

Schuster suggests polar bears survived those warm times by retreating to areas of continuing cold and ice, such as Norway’s Svalbard region. But he acknowledges his results are likely to be used by those who argue the bears aren’t endangered by current shrinking sea ice caused by climate change.

“I could easily see that either side of the climate discussion would try to use the results we present for their purposes.”

Schuster adds that some scientists even opposed publication of his research out of fear it would be misinterpreted by climate change skeptics.

“Politics should stay out of science,” he says. “Our key interest is to understand biological diversity.

“We’re also trying to understand this rate of change that happens in mammalian populations. It should be used as a data point, not for any political purposes.”

Schuster says the polar bear findings confirm a growing body of knowledge showing how quickly evolution can happen. He points to an adaptation in humans that allows adults to digest milk. That ability only developed about 8,500 years ago after agriculture was invented.

Still, Lindqvist warns that polar bears may have become so used to their icebound environment that it would be much harder for them to adapt this time — especially given the speed at which the Arctic is changing.

“The polar bear may be more evolutionarily constrained because it is today very specialized. Climate change now may be occurring at such an accelerated pace that we do not know if polar bears will be able to keep up.”