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Study estimates date of polar bears' split from brown bears

Yereth Rosen

A new polar bear genetics study has come up with a relatively recent estimate for the time when those bears separated into a species apart from brown bears.

The study, conducted by an international team of scientists and published in the academic journal Cell and summarized in the journal Nature, puts the split date at about 400,000 years ago, much more recent than the dates postulated in other studies.

The study analyzes the genes of 79 Greenland polar bears and 10 brown bears from Scandinavia, Alaska and Montana. It also identifies a particular gene that allows polar bears to roam the Arctic carrying fat that composes up to half of their body weight, relying on a diet with sky-high cholesterol levels that could trigger heart attacks and other cardiac problems in humans. That gene was likely an adaptation for the species, allowing polar bears to consume and store the very high amounts of fat they need to stay warm in the Arctic without the affliction of plaque accumulating in their arteries.

Among the genes analyzed were those of brown bears from Southeast Alaska's Admiralty, Baranof and Chichagof islands, also known as the ABC Islands, home of the modern brown bears with the closest known genetic links to polar bears. One recent study postulates that today's ABC bears are the descendants of polar bears stranded at the end of the last Ice Age on the formerly ice-bound islands and brown bears that migrated to the area.

Conclusions of the study published in Cell vary from those in another recent study, co-authored by Matt Cronin of the University of Alaska Fairbanks, that estimated the polar bear-brown bear split occurred 1.2 million years ago.


By YERETH ROSEN
yereth@alaskadispatch.com