Scientific American: Climactic changes might currently be threatening the survival of polar bears (Ursus maritimus), but similar shifts appear to have played an important part in bringing the species into existence in the not too distant past. Researchers announced today that they have sequenced the mitochondrial genome of an ancient polar bear. The genetic traces they found in the bear’s 110,000- to 130,000-year-old jawbone reveal that the species likely split from brown bears (U. arctos) just 150,000 …