An analysis of the polar bear genome has determined the species is about 8 times older than scientists previously thought.

The species had been thought to be some 600,000 years old. However, scientists from 13 North American universities have found that polar bears originated some 4-5 million years ago, when they diverged from brown bears, researchers say.

Scientists sequenced genomes of brown and polar bears, as well as the grizzly bear, using genetic samples of different time periods. The genetic studies revealed that polar bears have much in common with grizzlies, which inhabit southeastern Alaska (some 5-10% of their respective genomes coinside). These two species interbred during warm periods when their habitats overlapped.

Researchers have created a computer model showing the interdependence of the polar bear's genetic evolution, their population numbers and climate fluctuations on the planet. The model has shown that the number of polar bears increased during early Pleistocene age, when the climate was cooling, and gradually declined during warm periods.

Today, the number of polar bears is the lowest in the species' entire existence, experts say. The decline in population is most likely due to the animals having lost diversity in the polar bear gene pool throughout the ages, and now they are much less resistant to environmental changes than ever. Polar bears have endured many climatic changes. However, this does not ensure the species' survival in the future, researchers say.