Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage

Abstract

Ancient Bears Polar bears are well known for adapting to their cold Arctic climate. Some recent studies, based on mitochondrial DNA, concluded that they are a relatively young species and that these adaptations occurred quite quickly. Although mitochondrial DNA is regularly used to estimate evolutionary history, it has some well-known drawbacks, including sex-biased dispersal and hybridization. Thus, Hailer et al. (p. 344 ) looked at neutral genetic data that are distributed more widely across the genome of a relatively large sample of polar, brown, and black bears. Consistent with fossil-based studies, the analysis reveals polar bears as a sister lineage to all brown bears, with an estimated divergence time of 300,000 to 900,000 years ago. Thus, polar bears are indeed of a more ancient lineage, and more recent estimates based on mitochondrial DNA are likely to have been affected by past hybridization with brown bear.