All polar bears came from Ireland, claim scientists who have revealed that the animals descended from a single female brown bear living in the European nation during last Ice Age, around 10,000 to 110,000 years ago.
An international team claims that although polar bears existed before that time having evolved from a different group of brown bears in Siberia 200,000 years ago, Irish bear is their earliest known common ancestor.
The scientists explained that climate changes affecting the North Atlantic ice sheet probably gave rise to periodic overlaps in bear habitats. These overlaps then led to hybridisation — an event that caused maternal DNA from brown bears to be introduced into polar bears.
In their study, the scientists studied samples of DNA taken from the bones and teeth of 242 brown bears and polar bears, including modern animals and fossilised bears that lived 120,000 years ago.
The analysis found that the mitochondrial DNA of living polar bears closely matches the genetic material taken from female brown bears living in Ireland 20,000 to 50,000 years ago, the British media reported.
As well as the different skin and coat colours, polar bears are larger than brown bears, and have a different tooth structure. Polar bears live in the Arctic and are expert swimmers while brown bears are climbers that prefer mountain forests, say the scientists.
Lead scientist Prof. Mark Thomas said: “Interbreeding between brown bears and polar bears is usually thought of as a dead end. But this shows it happened before and is part of the evolution of both species.”
He added: “The odd thing is that although polar bears and brown bears have been around for a long time, and are clearly different, these Irish brown bear genes have swept through polar bears so quickly.”
During the last Ice Age, polar bears roamed much further south than the Arctic. At the time, Britain was connected to the rest of Europe by a land bridge, while ice sheets linked Britain with Ireland.
Scientists say the findings could help protect the polar bear which is an endangered species.
Dr. Beth Shapiro, a team member, added: “We know that the two species have interbred opportunistically and probably on many occasions during the last 100,000 years. Generally, this seems to happen when climate changes force the bears to move into each other’s habitats. When they come into contact, there seems to be little barrier to them mating.”
The findings have been published in the Current Biology journal.