Scientists had previously thought that polar bears had adapted to Arctic conditions at a prodigious speed – evolving from its nearest relative, the brown bear, in just 150,000 years.
This is the evolutionary equivalent of the bat-of-an-eyelid – other mammal species took millions of years to separate from one another.
But an international team of researchers at the Frankfurt Biodiversity and Climate Research Centre (BIK-F) have now scotched the speedy evolution theory.
"Our study shows a markedly different picture," biologist Frank Hailer told Die Zeit weekly. "These animals are a completely unique branch in the bear family tree."
The researchers compared genetic material from 19 polar bears, 18 brown bears and seven black bears, to complete the most thorough genetic analysis of the polar bear ever, which has now been published in the journal Science.
The polar bear's natural habitat has made studying the ancestry of polar bears particularly difficult – because they lived on floating marine ice, there are hardly any fossils of ancient polar bears. All traces of these animals have either sunk to the bottom of the polar oceans or been crushed and buried by shifting glaciers.
As a result, the oldest known evidence of polar bears is less than 120,000 years old.
"Previous studies have only taken small pieces of the available genome information into account," said Hailer. The new Frankfurt study, however, took samples from across several bear populations, creating a more reliable analysis of the genome.
But Hailer admits that the analysis is far from complete, and that they are yet to break the entire DNA code.
The Frankfurt team is yet to unpick exactly when the polar bear became white and started eating sea-lions for dinner. "We don't know yet what it will reveal about the history of the adaptation process," said Hailer.
Even dating the origins of the polar bear to 600,000 years ago is still a rough guess, but it places Knut's earliest ancestor in the Pleistocene era, at a time when temperatures on the planet sank considerably.
"The original polar bear could have been a more southern bear, like all the other bears of today," said Hailer.