Shamrocks, Saint Patrick, and… Polar Bears?

What could be more Irish than a polar bear? Nothing, say Penn State gene researchers. Because all polar bears are Irish immigrants:

Polar and brown bears are vastly different species in terms of body size, skin and coat color, fur type, tooth structure, and many other physical features. Behaviorally, they are also quite distinct: Polar bears are expert swimmers that have adapted to a highly specialized, arctic lifestyle, while brown bears — a species that includes Grizzlies and Kodiaks — are climbers that prefer the mountain forests, wilderness regions and river valleys of Europe, Asia and North America.

“Despite these differences, we know that the two species have interbred opportunistically and probably on many occasions during the last 100,000 years,” [biology professor Beth] Shapiro said. “Most importantly, previous research has indicated that the brown bear contributed genetic material to the polar bear’s mitochondrial lineage — the maternal part of the genome, or the DNA that is passed exclusively from mothers to offspring. But, until now, it was unclear just when modern polar bears acquired their mitochondrial genome in its present form.”

Although previous researchers had suggested that the ancient female ancestor of modern polar bears lived on the ABC Islands — the Alaskan islands of Admiralty, Baranof, and Chichagof — only 14,000 years ago, Shapiro’s team found evidence of a much earlier hybridization event.