Monday, December 10, 2007

Tell us of your beginnings, old bear

Polar bears' white hair doesn't come from age; they are the youngest of all bear species. However, they are older than we previously thought.
What may be the oldest known remains of a polar bear have been uncovered on the Svalbard archipelago in the Arctic.

The jawbone was pulled from sediments that suggest the specimen is perhaps 110,000 or 130,000 years old.

Professor Olafur Ingolfsson from the University of Iceland says tests show it was an adult, possibly a female.

The find is a surprise because polar bears are a relatively new species, with one study claiming they evolved less than 100,000 years ago.

The difference is bigger than mere years indicate. One hundred thousand years means the polar bear evolved during an early pulse in the last ice age. That a snow and ice adapted creature might have evolved during a period when much of the Northern Hemisphere was covered in snow and ice make sense but isn't necessarily true. The part of the North covered by snow and ice for the last ten thousand years has been plenty large for polar bears to thrive.

And now it appears that they might have evolved in a climate more like the present than like an ice age. A date of 110,000 or 130,000 years ago pushes this fossil into the last full interglacial. All that it would take for a polar animal to evolve during an interglacial would be for the northern part of an species' population to become genetically isolated from the majority of the species--in this case brown and grizzly bears. Selection pressures among that northern group would favor those with traits better adapted to the cold and white world. Color and camouflage are a very important trait for a hunter. Meanwhile, their southern cousins would keep those traits better adapted to forest and tundra, like brown fur.

Aside from mere scientific interest, this story has a hopeful element. The Eemian--the last interglacial--was much warmer than the present interglacial. This means if the world doesn't warm too much, we might be moving into a period similar to the one that created polar bears.

On the other hand, we shouldn't get complacent. There is a lot more to the bears' environment than cold temperatures and ice. They are just one part of a complex and fragile ecology. Even if the bears can handle the temperature and loss of ice, they still need a food supply that survives the shifting climate along with them. Seals, salmon, walruses, and who knows what else all need to make the change and feed each other. The more we know, the better we can help them.

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