Polar bears traced back to Britain

All polar bears originate from a single ancestor which lived in Britain or Ireland about 50,000 years ago, according to DNA study by scientists. New evidence from fossils found in Irish caves shows that modern polar bars evolved from a single female brown bear at the peak of the last ice age.

Despite the significant differences between polar bears, which are expert swimmers, and brown bears, which are better climbers, the species have often come into contact over the past 100,000 years during periods of unusually hot or cold weather.

A genetic marker carried by every polar bear alive today proves that they all descend from the same female brown bear, who bred with a polar bear to create hybrid offspring.

It had been assumed that this took place in Alaska 14,000 years ago, but now analysis of 242 brown bear and polar bear DNA samples from the past 120,000 years show the hybridisation of the two species occurred much earlier.

Fossils found in Irish caves show that polar bears in fact began carrying the DNA of the female brown bear between 20,000 and 50,000 years ago, before brown bears disappeared from the British Isles.

The study, led by Dr Beth Shapiro of Penn State University in the USA and Prof Daniel Bradley of Trinity College Dublin, was published in the journal Current Biology.

Dr Shapiro said: “Previous research has indicated that the brown bear contributed genetic material to the polar bear's mitochondrial lineage – 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."

By Nick Collins, Science Correspondent
http://www.telegraph.co.uk/earth/wildlife/8622987/Polar-bears-traced-back-to-Britain.html