Polar bear is a 'new' species

by Jonathan LEAKE

Polar bears may have come into existence only 150,000 years ago, when trapped brown bears had to adapt to an ice age Polar bears may have come into existence only 150,000 years ago, when brown bears were trapped by an ice age and had to adapt quickly to survive, scientists have found.

The suggestion follows the discovery of the jawbone of an animal that died up to 130,000 years ago, making it the oldest polar bear fossil found.

The bone has yielded new insights into the origins of Earth's largest land predator. One is the possibility that polar bears owe their existence not only to past climate change, including ice ages, but have also survived at least one long period of global warming.

The bone was discovered at Poolepynten on the Arctic island of Svalbard by Professors Olafur Ingolfsson, of the University of Iceland, and Oystein Wiig, of the University of Oslo.

In a research paper they concluded: "The Poolepynten subfossil mandible, which we argue is from a fully grown male, is probably the oldest polar bear find discovered so far. Its true age is interpreted to be 110,000-130,000 years old."

The bone has since been subjected to analyses that could help to clear up the debate over when polar bears first appeared. Some academics believe they evolved 50,000 years ago, while others put the date at more than 1m years ago. The existence of the Svalbard fossil indicates that polar bears were already a distinct species by about 130,000 years ago. But anatomical and DNA evidence from the fossil indicate a closeness between polar bears and brown bears of the time - suggesting the species diverged no more than about 200,000 years ago and probably about 150,000 years ago.

This sharply narrows the "window" during which polar bears might have emerged to a period when the northern hemisphere was being sucked into an ice age that lasted from 190,000 to 130,000 years ago. This change of climate would have pressurised brown bears, especially those trapped on islands, to adapt to cold and ice. One research group, led by Gerald Shields, of the University of Alaska Fairbanks, used DNA from 61 brown bears taken from three populations in Alaska and 55 polar bears from Arctic Canada and Siberia. The scientists wanted to work out not only when polar bears evolved but also, potentially, where from.

They found a population of brown bears living on the Alaskan islands of Admiralty, Baranof and Chichagof, known as the ABC islands, which lie adjacent to each other. The DNA of those bears was closer to that of polar bears than any other brown bear population.

In a paper they said: "Brown bears of the ABC islands may be descendants of ancient ursids [bears] that diverged from other lineages of brown bears and subsequently founded the polar bear lineage." This view is expected to get support from new research, out this week, based on DNA extracted from the Poolepynten jawbone.

It means polar bears have already survived a global warming that affected the northern hemisphere from 130,000 to 115,000 years ago, when the Greenland ice sheet and the Arctic ice cap were smaller than now. Professor Chris Stringer, of the Natural History Museum in

London, an expert in ice ages, said: "Early polar bears would not have had all the specialisations of modern animals and we know nothing about their behaviour.

"Living through a warm period back then does not mean they are resilient to climate change now."

- Timesonline.co.uk