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Polar bears and brown bears have interbred opportunistically and probably on many occasions during the last 100,000 years. An international research team concluded that all living polar bears trace their maternal ancestor to a brown bear that lived near present-day Britain and Ireland just prior to the last ice age.
The research team analyzed 242 brown bear and polar bear mitochondrial lineages sampled throughout the last 120,000 years and across multiple geographic ranges. They found that the fixation of the mitochondrial genome likely occurred during or just before the peak of the last ice age, possibly as early as 50,000 years ago. The specific population of brown bears that shared its maternal DNA with polar bears has been extinct for roughly 9,000 years.Image credit: Daniel J. Cox/NaturalExposures.com
