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Jawbone shows evolution of polar bears
Specimen found in Svalbard shows animals descended from brown bears 150,000 years ago

This polar bear jawbone from Svalbard is the oldest known specimen. Photo provided by The University Centre In Svalbard.

Polar bears came into existence by evolving during a period of climate change, but might not be so adaptable to modern global warming, according to scientists studying a jawbone fossil discovered in Svalbard.

The jawbone from a bear that died 110,000 to 130,000 years ago was found in 2004 during a geology excursion to Poolepynten by The University Centre In Svalbard. Researchers said in January it is the oldest polar bear fossil ever found and indicated it could provide critical data about the species' evolutionary history.

A paper co-authored by 14 researchers states the find suggests polar bears originated by evolving from brown bears during an ice age 150,000 years ago. That makes the polar bear a young species in the evolutionary cycle and one that adapted quickly to changing conditions.

Past opinions about the origin of the polar bear have ranged from 50,000 to more than 1 million years ago. The DNA of the jawbone discovered in Svalbard was compared to polar and brown bears in Alaska, with evidence suggesting brown bears evolved to cope with the ice age's cold.

"By very early in their evolutionary history, polar bears were already inhabitants of the Artic sea ice and had adapted very rapidly to their current and unique ecology at the top of the Arctic marine food chain," the study notes.

That means polar bears also survived a period of global warming 130,000 to 115,000 years ago. But just because they adapted then doesn't mean they can do the same during the drastic transformation scientists say the Arctic is now experiencing.

"Early polar bears would not have had all the specializations of modern animals and we know nothing about their behavior," said Chris Stringer, a professor at the Natural History Museum in London, in an interview with The Sunday Times. "Living through a warm period back then does not mean they are resilient to climate change now."

The next step for researchers will be studying the fossil's genom in an attempt to reconstruct the polar bear's entire evolutionary history.
UNIS students "stumbled" across the 23-cm fossil during their 2004 summer excursion, according to the university. The specimen was originally thought to be a female, but further study indicates it is a fully grown male similar in size to today's creatures.

The sediment in which the jawbone was found was deposited during a period of high relative sea levels, subsequent to a regional deglaciation, suggesting advection of relatively warm North Atlantic water to the site at the time, the UNIS report adds. The fossil is also exceptionally well preserved, likely due to a combination of burial in fine-grained marine sediments and permafrost conditions.

The find, announced publicly in 2007, was hailed as "spectacular" because it was the oldest such specimen by at least 40,000 years. That allowed for analysis of how they might have endured the period of climate change.

A polar bear cub and its mother drift on a rapidly shrinking iceberg about 12 miles offshore in Olga Strait. Eric Lefranc, who took this photo during a Svalbard cruise, told news organizations this week the mother could likely swim to shore, but "our guide was quite pessimistic about the survival of the cub."

"This find tells us that the polar bear has the capacity to survive a warmer climate, such as we are experiencing now," said Ólafur Ingólfsson, a University of Iceland professor who led the excursion during an adjunct term at UNIS, at the time of the public announcement.

Media reports during the past week about the polar bear's ability to evolve during climate change occurred at about the same time photos of a cub and its mother stranded on a tiny iceberg in Svalbard were also getting widespread publicity. Eric Lefranc, a wildlife photographer who captured the bears on film during a cruise in Olga Strait, said a guide indicated the mother could probably swim the 12 miles to shore, but the cub would likely drown.

Such photos and indicated have been used commonly to illustrate the peril bears are facing from modern warming. But a vast majority of readers responding to the two stories didn't seem to have much sympathy.

"Why would not the polar bears be resilient to climate change now?" wrote one commenter claiming to be Dr. Alok Bhattacharyya of London. "Have they changed their lifestyle? Have the children polar bears been given mobile phones, ipods, etc. by their parents? Have they been chatting on Facebook for hours? If the polar bears have been running their lives as they always did, we do not need to worry too much about them."

The full study can be read or downloaded at www.pnas.org/content/early/2010/02/18/ 0914266107.full.pdf+html.

Published in the March 2, 2010, print edition.

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