Polar bears and grizzly bears continue to mate and could evolve into new species

Polar bears and grizzly bears have mated for thousands of years, according to a new study, and as climate change intensifies, they may one day evolve into new species.

According to the findings of researchers from the University at Buffalo, published in the Proceedings of the National Academy of Sciences– DNA data from an ancient polar bear tooth shows that there was “at least one ancient event of brown bear introgression into the ancestor of polar bears, possibly dating back more than 150,000 ” year.

This differs from existing research and “may have implications for our understanding of the impacts of climate change”, according to the study.

Genetically, polar bears have evolved to be adapted to arctic conditions – for example, their small ears minimize heat loss. However, over the years, their population has been affected by fluctuations in climate. As a result, scientists found evidence that grizzly bears, coming from further south, were mating with polar bears, altering their genetic makeup.

A photo shows an ancient polar bear tooth. Researchers have studied this to learn more about brown bears and grizzly bears that bred in the past.
Karsten Sund, NHM Natural History Museum, University of Oslo

And as climate change intensifies, it could happen again.

Charlotte Lindqvist, an associate professor of biological sciences at the University of Buffalo College of Arts and Sciences and an expert in bear genetics, said Newsweek that scientists don’t know exactly when the species began interbreeding after splitting from a common ancestor more than a million years ago.

“We know that they are still able to mate today and can produce fertile offspring, so they may have mated intermittently since their species split, whenever the two species are contacted,” Lindqvist said. “The older a mating event is, the harder it is for us to find evidence of it in today’s populations. However, based on our study, we find DNA sharing with brown bears in modern polar bears and this also involves one-year-old polar bears. This suggests that mating occurred before the age of this ancient polar bear.”

Brown bears are called grizzlies in North America.

Lindqvist said that while it’s clear the two species can mate and produce fertile offspring, there are “several reasons” why this hasn’t happened extensively over the past millennia.

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

“Although there is evidence of brown bear-polar bear hybrids in recent years in the Canadian Arctic, contemporary hybridization appears to be sparse, possibly caused by unusual and atypical mating preferences of selected individuals” , she said.

However, if the two species start to come into more and more contact due to climate change altering their habitats, Lindqvist said it’s likely we’ll see more interbreeding between the two species.

This could eventually result in entirely new species.

“Species evolve all the time and there’s no guarantee that new bear species won’t appear in the future, but it probably won’t be in our lifetimes,” Lindqvist said.

“And that raises the general question of what a species really is! What is more likely to happen, unfortunately, is the disappearance of the polar bear if it continues to lose its main habitat, the sea ice. Arctic.”

A photo shows a grizzly bear and a polar bear. Polar bears and grizzly bears have mated for millennia, according to a new study, and as climate change intensifies, they may one day evolve into new species. (DrDjJanek / James B Williams Photography)
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