Assertion: female brown bear | /r/HasProperty | unwilling to swim
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text: This appears to reflect a process in which a population of polar bears was left behind as the species retreated northwards at the end of the last ice age, with male brown bears subsequently introducing genes from the adjacent mainland, but female brown bears being generally unable or unwilling to swim across several km of open ocean to reach the islands (thus the lack of exchange of mitochondrial DNA).