Polar Bears and Grizzlies Keep Mating and Could Evolve Into New Species

Polar bears and grizzly bears have mated for thousands of years, a new study has found—and as climate change intensifies, they could one day evolve into new species.

According to findings by researchers at the University of Buffalo—published in the Proceedings of the National Academy of Sciences—DNA data from an ancient polar bear tooth shows there was "at least one ancient introgression event from brown bears into the ancestor of polar bears, possibly dating back over 150,000" years.

This differs from existing research and "may have implications for our understanding of climate change impacts," the study said.

Genetically, polar bears developed to be suited to Arctic conditions—for example, their small ears minimize heat loss. However, over the years, their population was affected by fluctuations in the climate. As a result, scientists have found evidence that grizzly bears, coming from further south, mated with polar bears, modifying their gene pool.

Polar bear jaw
A picture shows an ancient polar bear tooth. Researchers studied this to find out more about brown bears and grizzly bears breeding in the past. Karsten Sund, Natural History Museum NHM, University of Oslo

And as climate change intensifies, this may occur again.

Charlotte Lindqvist, an associate professor of biological sciences in the University at Buffalo College of Arts and Sciences, and bear genetics expert, told Newsweek that scientists are not exactly sure when the species began to interbreed after they split from a common ancestor over 1 million years ago.

"We know they are still able to mate today and can produce fertile offspring so they may have been mating off and on since their species split, whenever the two species came into contact," Lindqvist said. "The older a mating event is, the more difficult it is for us to find evidence of it in today's populations. However, from our study we find sharing of DNA with brown bears in modern polar bears and it also involves a 115,000-130,000- year-old polar bear. This suggests mating happened before the age of this ancient polar bear."

Brown bears are called grizzlies in North America.

Lindqvist said that despite it being clear that the two species can mate and produce fertile offspring, there are "several reasons" it has not happened extensively over the last millennia.

One potential reason is that the species' geographic ranges do not overlap over most of their distribution.

"Although there is evidence for brown bear–polar bear hybrids in recent years in the Canadian Arctic, contemporary hybridization seems sparse, possibly caused by uncommon and atypical mating preferences of select individuals," she said.

However, if the two species start coming into increasing contact as a result of climate change altering their habitats, Lindqvist said it is likely we will see more interbreeding between the two species.

This could eventually result in entirely new species.

"Species evolve all the time and there is nothing to say that new species of bears won't appear in the future, but it will likely not be in our lifetime, Lindqvist said.

"And it brings up the general issue of what a species really is! What may be more likely to happen, unfortunately, is the demise of the polar bear if it continues to lose its main habitat, the Arctic sea ice."

A photo shows a grizzly bear and a polar bear. Polar bears and grizzly bears have mated for millennia, a new study has found—and as climate change intensifies, they could one day evolve into new species. ( DrDjJanek / James B Williams Photography) iStock / Getty Images