Page "Polar bear" Paragraph 6

The evidence from DNA analysis is more complex.

The mitochondrial DNA ( mtDNA ) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150, 000 years ago.

Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears, meaning that the polar bear would not be a true species according to some species concepts.

The mtDNA of Irish brown bears is particularly close to polar bears.

A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603, 000 years ago, although the latest research is based on analysis of the complete genomes ( rather than just the mitochondria or partial nuclear genomes ) of polar, brown and black bears, and establishes the divergence of polar and brown bears at 4-5 million years ago.