If true the polar bears have survived an iceless Arctic during several periods, which will dent their iconic “global warming” status somewhat. We knew, of course, that they had certainly survived the Holocene Climatic Optimum, significantly warmer than now but this suggests they successfully negotiated at least two prior interglacials which were supposed to be a couple of degrees (C) warmer again.
Investigating Mysteries of Polar Bears’ Ancestry With a DNA Lens
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.