Polar bears are not a pretty recent (~150,000 million years ago) offshoot of brown bears, that then adapted to Arctic conditions quickly, as previously thought. That idea had come from mitochondrial DNA study, and from some evidence that there have been some recent interbreeding between brown and polar bears. Mitochondrial DNA studies are useful, but they give an incomplete picture of evolution because mtDNA is transmitted only through the maternal lineage. A new analysis of 14 segments of nuclear DNA of polar bears, brown bears, and black bears reveals that brown bears and polar bears had a common ancestor that split from black bears approximately 600,000 years ago. Analysis of the whole genome of all 3 species is needed to pinpoint the exact date of the split. Apparently the mtDNA comes from a mating between extinct Irish brown bears and polar bears about 130,000 years ago, at times of environmental stress that caused a population bottleneck. The brown bear mitochondrial DNA then spread to the whole polar bear population.
Polar bears, long thought to have branched off relatively recently from brown bears, developing their white coats, webbed paws and other adaptations over the last 150,000 years or so to cope with life on Arctic Sea ice, are not descended from brown bears, scientists report.
Instead, according to a research team that looked at DNA samples from the two species and from black bears, the brown bear and polar bear ancestral lines have a common ancestor and split about 600,000 years ago.
The report, published online on Thursday in the journal Science, is the latest attempt to understand the surprisingly murky origins of one of the most familiar animals on earth, and a potent environmental symbol because it is losing the sea ice it depends on to a warming climate. Because of climate change, and threats from shipping, hunting and pollution, the polar bear is listed as “vulnerable,” one level below endangered, by the International Union for Conservation of Nature.
The report comes to no conclusion about how sensitive the bears are to the current loss of the sea ice that they live on, and the evolutionary tale it presents can be read in different ways.
The findings challenge the idea that the bears adapted very quickly, but confirm that they have made it through warming periods and loss of sea ice before. It may have been touch and go for the bears, however, because the authors find evidence of evolutionary bottlenecks, probably during warm periods, when only small populations survived, even though warming was occurring much more slowly than it is now.
What they found, Dr. Hailer said, was that polar bears “are older and much more genetically unique” than had been thought. Other studies in the past few years suggested that the species was “a very recent offshoot from brown bears,” he said, dating from about 150,000 years ago.
Read the rest here.
You meant 6,000 years, correct? =)
No, she means further back in time thus 600,000 years/
ScienceDaily (Apr. 20, 2012) — A study appearing in the current issue of the journal Science reveals that polar bears evolved as early as some 600,000 years ago. An international team led by researchers from the German Biodiversity and Climate Research Centre (BiK‐F) shows the largest arctic carnivore to be five times older than previously recognized. The new findings on the evolutionary history of polar bears are the result of an analysis of information from the nuclear genome of polar and brown bears, and shed new light on conservation issues regarding this endangered arctic specialist.
But doone, the Earth is only 6,000 years old! :-P
Damn right, just ask Pat Robertson. =)
This one's a keeper. =)