Ancient DNA from rare fossil reveals that polar bears evolved recently and adapted quickly

DNA from a rare, ancient polar bear fossil is yielding information about the response of the species to the devastation wrought by past climate changes. Analyses of the fossil's DNA reveals key pieces of the evolutionary history of both polar bears and brown bears. The fossil's DNA is, by far, the oldest mammal mitochondrial genome to be sequenced -- about twice the age of the oldest genome sequence from a woolly mammoth.