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Scientists uncover hidden history of polar bears
It all started with a fossil.
“We have this polar bear jawbone from the Svalbard archipelago in the North Atlantic,” says Charlotte Lindqvist, a professor at SUNY Buffalo and lead author of a landmark new study into the history of polar bears.
An ancient species
Lindqvist, along with researchers from over two dozen institutions, assembled the ancient polar bear’s genome from this 130,000 year old bone. As one of the oldest polar bear remains ever found, this toothless facial fossil opened a window for scientists to guess how the animal survived past periods of climate change.
The study -- published earlier this week in the journal Proceedings of the National Academy of Sciences -- also determined the polar bears species to be about four to five million years old – more than seven times older than previously thought.
Another study published in Science in April pegged the age of the species at just 600,000 years.
This fossil also showed a strong genetic link between polar bears and brown bears, resulting from intermingling as recent as a few hundred thousand years ago. Researchers found the two species have shared close quarters throughout history, depending on shifting nature of glacial ice and land.
The study is the most extensive analysis to date of polar bear DNA. Scientists compared bear genomes with fossils from multiple periods of history.
“That gave us an idea of the maternal line of the polar bear and its relationship with brown bears,” says Lindqvist.
The mating of the two animals created a diversity of genes in polar bears that allowed for a greater ability to adapt to changes in habitats due to earlier periods of warming and cooling.
Coping with climate change
“During these warming periods, the polar bear population probably contracted into these smaller pockets where there was suitable environment for the polar bears to survive. Then as the climate cooled again, they expanded from the smaller populations into a larger area,” she says.
Polar bears have easily identifiable genetic differences from brown bears, like darker skin pigmentation, that allow the white-furred creates to survive the harshest of Arctic climates. Partly due to location, polar bears also pursue a different diet and produce milk with a higher fat content.
Most modern day brown bears only contain about two percent polar bear DNA. But those living in the Alaskan islands can have up to 10 percent – a vestige of when the earth’s warmer climate brought the two species together.
Yet based on a few aspects of animal classification, some doubt the notion that polar bears and brown bears are technically different species.
Still, compared to brown bears, the population of polar bears has been in decline for thousands of years. Over time, this has created a shallow gene pool, making the animals less resistant to changes to ongoing changes in the environment.
"No guarantee" they will survive
“It looks like from our study that the polar bear population in general has gone through a very drastic decline and we know today that polar bears hold very little genetic diversity,” Lindqvist says.“So even if polar bears have survived warming periods in the past, it’s certainly no guarantee that they will survive in the future."
In addition to heat and loss of habitat, increasing concentrations of heavy metal pollution in the Arctic also threatens polar bears.
“Certainly it seems like changes in the environment and the changes in climate today happens at a much faster pace than it has happened before.”
With many of the changes in the earth’s climate considered rapid and unprecedented, Lindqvist says scientists are unsure how polar bears will ultimately fare.
“I wish I could look into my crystal ball and tell you what is going to happen,” she says.
You can follow reporter Daniel Robison on twitter @robisonrobison.