BY PAT SUMMERS

NEWJERSEYNEWSROOM.COM

Polar bears – huge, white and threatened by climate change – turn out to be an older species than scientists had thought. Just as people begin to wonder about their future, polar bears’ past now stretches back some 4 million years.

Till modern techniques allowed scientists to study polar bears more closely, it had been thought they split off from brown bears a mere 600,000 years ago, but not so. Research has long been hampered by the fact that living where they do, polar bears are typically buried at sea and their remains are lost.

For the history of polar bear evolution, scientists had to wait to investigate the DNA of living related species. This can work as a kind of microscope to look at events as the species separated.

A new study, just reported in Proceedings of the National Academy of Sciences, looked at the full genomes of polar bears, brown bears and black bears, reports the NYTimes.

The scientists learned that about the same time as black bears became a distinct species, polar bears and brown bears had split apart, remaining so for long enough to build up separate genetic profiles, reports CSMonitor.com.

The research team also found evidence that since the species split off into three distinct bear varieties, polar bears and brown bears have intermittently interbred, probably prompted by warming periods when polar bears were forced onto land and brown bears moved north.

Now, with Arctic warming apparently underway, polar bears’ individual species identity may be in greater jeopardy than their survival. They may have to move toward a renewed merger with brown bears. According to USAToday, if polar bears are forced to spend more and more time on land, their continued interbreeding with brown bears could result in the loss of polar bears as a distinct species.

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Freelance writer Pat Summers also blogs at www.nj.com/pets.