This item is restricted to only allow viewing of the metadata.
A scan of recent titles from the molecular systematics literature finds the species tree of bears to be a classic “cloud of gene histories” punctuated by rapid events of divergence. As a result, the phylogeny of bears has been complicated by cross species hybridization and the incomplete sorting of ancestral polymorphism. It should come as no surprise then that the topology of the phylogenetic species tree of brown bears and polar bears is not always in agreement with estimations drawn from individual gene trees – most prominently those based on mitochondrial DNA (mtDNA). Our results from nuclear DNA (nDNA) sequence comparisons of polar bears, brown bears and black bears disprove the viewpoint from phylogenetic assessments of mtDNA that polar bear and brown bear diverged just 160,000 years ago. Calibrations of our data with nDNA divergences between polar bear–panda and polar bear–spectacled bear indicate that polar bears and brown bears separated more than 0.6 million years ago. Polar bears are an ancient sister lineage to brown bears and, as a consequence, have lived through several previous warm interglacial phases. Threats to their survival unique to this current phase will also be discussed.
Click tabs to swap between content that is broken into logical sections.