Actually, Canada’s polar bears have always had Irish ancestry. It’s just topical to talk about it on St. Patrick’s Day.
The Irish connection was made last year when a worldwide team of researchers realized that the modern polar bear’s mitochondrial DNA is closely related to DNA in the bones of brown bear skeletons found in eight cave sites around Ireland. The Irish brown bear became extinct about 3,000 years ago.
Previously the general consensus had been that polar bears were descended from brown bears on the Siberian side of the Arctic, not the Atlantic side, and the genetic digression took place about 100,000-150,000 years ago. But the most recent study has concluded that all existing polar bears can be genetically traced back to one Irish brown bear mama (the “Eve” of polar bears) and the lineage is much more recent than previously thought — only 20,000-50,000 years old.
The study was conducted by researchers from across Europe (including Scandinavia and Russia) and North America, with the the final connection being made by scientists in Ireland, Britain and the U.S. Here’s a link to the abstract of the group’s paper published in the scientific journal Current Biology in July 2011.
The conjecture is that multiple matings took place during the last ice age. Well, actually we’re still technically in the tail end of an ice age that started about 2.5 million years ago, so it would be more accurate to call it the “Würm glaciation period” that extended from about 110,000 to 15,000 years ago.
At the height of that glaciation period (about 22,000 years ago) the whole northern part of the globe from Siberian Asia to Canada to Greenland to Scandinavia and Europe, including the islands of Britain and Ireland, was covered in giant ice sheets. Thus the movement of various polar species, including bears, was widespread and led to substantial interbreeding with more southerly species around the edges of the icesheets.
That’s the thesis anyway and the explanation for why Canada’s polar bears can trace their ancestry back to a lady brown bear in Ireland.
What can’t be explained, however, is why the polar bears seen below are displaying behaviour more usually associated with the aftereffects of St. Patrick’s Day celebration. Go figure.