It is a well-known fact that the brown bear and the polar bear are closely related. Reproduction in captivity has been recorded. And from analyses of mitochondrial DNA it is undisputed that polar bears constitute a lineage within the genetic diversity of brown bears. But, due to an extremely poor fossil record not much was known about the polar bear’s evolution and the moment of their divergence. In a recent publication in Proceedings of the National Academy of Sciences, researchers show that the polar bear branched off the brown bear lineage probably just 150,000 years ago.
Using advanced DNA technology they were able to compare DNA from a fossil polar bear jaw, excavated in Spitsbergen, with DNA from bears living at present times. Furthermore, using molecular dating and stable isotope analyses, they show that this “young” polar bear early in its evolutionary history, already was an inhabitant of the Artic sea ice and has adapted very rapidly to its current and unique ecology at the top of the Arctic marine food chain. All in all the polar bear provides an excellent example of evolutionary opportunism within a widespread mammalian lineage.
(Source: PNAS (Early Edition), 01.03.2010)