Investigating Mysteries of Polar Bears’ Ancestry With a DNA Lens

http://www.nytimes.com/2012/04/20/science/polar-bears-did-not-descend-from-brown-bears-dna-study-indicates.html?_r=1&ref=science#

It has long been thought that polar bears branched off from brown bears relatively recently, but that is now being refuted through DNA comparisons.  Now, DNA techniques have shown that the two have ancestral lines that split around 600,000 years ago.  This article does something interesting: relates it to the debated topic of global warming and polar bears, “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”.