The change in climate and genetic exchange has caused the polar bears and brown bears to reunite and interbreed, according to a new study.

A team of researchers from the Pennsylvania State University and the University of Buffalo (UB) sequenced the genome of polar bears and found that the polar bears were involved in interbreeding with brown bears some five million years ago. The climate change and the genetic exchange between the polar bears and the brown bears created the modern polar bears that we know.

After the initial interaction, the species separated due to climate change. Scientists now suggest that there is evidence which shows the brown and white species could be coming back together. Warmer temperatures are causing the sea to retreat in Arctic, which is native to these ice-dwelling species. This may result in polar bears spending more time on the land and provoke them to come in contact with the brown bears on the land and start interbreeding.

"Maybe we're seeing a hint that in really warm times, polar bears changed their life-style and came into contact, and indeed interbred, with brown bears," said Stephan Schuster, professor of biochemistry and molecular biology at Penn State and a research scientist at Nanyang Technological University in Singapore.

Researchers analyzed the genome of various bear species including the modern polar bears, three brown bears, one black bear and a 120-thousand-year-old fossil of a polar bear.

They found that the polar bears have similarities in their genetics with the ABC brown bears, a group from southeastern Alaska. Experts also noted that the polar bears are ancient species that date back to million years defying a recent study which suggested that the bear species are 600,000 years old.

Though the polar bears have been able to survive for millions of years, researchers warn that it does not assure the bears' future survival. Polar bears are sensitive to climate change. While they found that the population of the bear species were at an increasing level during colder periods, their number has significantly decreased during warmer times.

"They have indeed lost a lot of their past genetic diversity, and because of this, they are very likely more sensitive to climate change threats today," said Charlotte Lindqvist, an assistant professor of biology at UB.

The findings are published in the online journal Proceedings of the National Academy of Sciences