Polar bears 'evolved amid ice age'

Polar bears rapidly evolved their white fur and Arctic lifestyle as they adapted to an ice age environment, new genetic evidence suggests. Skip related content

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But despite surviving a return to warmer conditions, they may not be able to keep up with the accelerated pace of man-made climate change, say scientists.

The evolution of polar bears has presented a puzzle because their ancient fossils are so rare.
Usually, fossils are preserved in sediments. But because polar bears live on ice, their dead remains tend to fall to the bottom of the ocean or are removed by scavengers.
In 2004, scientists discovered a rare and well-preserved fossilised jawbone and canine tooth in Norway's Svalbard archipelago.
Analysis of DNA extracted from the specimens has now revealed important clues about the origins of polar bears.
Study leader Dr Charlotte Lindqvist, from the University at Buffalo, in New York State, US, said: "Our results confirm that the polar bear is an evolutionarily young species that split off from brown bears some 150,000 years ago and evolved extremely rapidly during the late Pleistocene, perhaps adapting to the opening of new habitats and food sources in response to climate changes just before the last interglacial period."
The late Pleistocene period was marked by extensive glaciation, with ice sheets covering much of the northern hemisphere. Many large animals became extinct during this time, including woolly mammoths, sabre-toothed cats and ground sloths, as did Neanderthal humans.
As the Pleistocene gave way to the Holocene about 12,000 years ago, the world became warmer and the ice retreated.
Polar bears continued to survive, confining themselves to the icy Arctic where they live to this day, by hunting seals.