LONDON - Scientists have found that the female ancestor of all polar bears was a brown bear, which lived in present-day Britain and Ireland during the last ice age 20,000 to 50,000 years ago.

Changes in climate affecting the North Atlantic ice sheet probably gave rise to periodic overlaps in bear habitats, which led to interbreeding between bears, causing maternal DNA from brown bears to be introduced to polar bears, according to a study by British and American researchers.

The findings, published online in the journal Current Biology, may help guide future conservation efforts for polar bears, which are listed as threatened under the US Endangered Species Act.