Polar bears' Irish ancestry exposed
It's a long way from the Arctic to Tipperary, but scientists have discovered polar bears can trace their family tree to Ireland.
Genetic evidence shows the furry white giants are descended from Irish brown bears that lived during the last Ice Age.
Modern polar bears share a distinct DNA sequence, passed down the female line, with their now-extinct brown ancestors.
However, the same DNA fingerprint is absent from other species of brown bear alive today. It is thought the link arose from interbreeding between prehistoric polar bears and female brown bears when their paths crossed as the Irish climate cooled.
Scientists made the discovery after analysing DNA in mitochondria - tiny powerplants in cells - that is only passed from a mother to her offspring.
The research, published in the journal Current Biology, was carried out by scientists from the US, Ireland, Belgium, Spain, Denmark, Russia and Sweden.
Dr Ceiridwen Edwards, from Oxford University, a member of the international team, said: "Hybridisation between ancient Irish brown bears and polar bears has led to the complete replacement of the original polar bear mitochondria. This maternal lineage is now present in all modern polar bears."
Polar and brown bears are hugely different physically and are also very distinct behaviourally. Polar bears, the world's largest carnivores, are expert swimmers which prey on seals, while forest-living brown bears climb and have a varied omnivorous diet. Yet the two appear to mate successfully whenever they come into contact.
Warmer periods may bring the species together as melting glacial ice and rising sea levels force polar bears to retreat inland.
"Environmental conditions appear to have played, and continue to play, a big part in the evolutionary history of polar bears," said Dr Edwards. "Today's warming climate is again bringing modern polar bears into contact with brown bears in places like Canada and Alaska."