The Arctic’s dwindling population of polar bears all descend from a single mama brown bear which lived 20,000 to 50,000 years ago in present-day Ireland, according to a study.

DNA samples from the great white carnivores –taken from across their entire range in Russia, Canada, Greenland, Norway and Alaska – revealed that every individual’s lineage could be traced back to this Irish forebear.

The analysis of genetic material inherited only through females also showed that brown and polar bears mated periodically over the last 100,000 years.

This raises the possibility that such cross-species mingling – thought by some scientists to be an additional threat to polar bears already struggling to cope with climate change – played a positive role in their recent evolution, the researchers said.

“Hybridisation could certainly result in the loss of unique genetic sequences, which could push them toward extinction,” said Beth Shapiro, a professor at Pennsylvania State University and lead researcher for the study.

“But scientists should reconsider conservation efforts focused not just on polar bears but also on hybrids, since hybrids may play an underappreciated role in the survival of certain species.”

Several “pizzlies” – a cross between a grizzly and a polar bear – have been spotted in recent years as the Arctic species has been pushed outside its familiar habitat by mounting temperatures and melting ice.

The fierce predators use the edge of the ice cap as a staging area to stalk seals, their preferred food.

Global warming has hit the Arctic two or three times harder than other parts of the planet, redesigning the environment in which dozens of terrestrial and marine mammals live.

It has long been known based on DNA and fossil evidence that polar bears – Ursus maritimus – branched off from the larger family of brown bears about 150,000 years ago.