Researchers extracted DNA from a 115,000-year-old polar bear jawbone and used it to analyze the genetic relationship between these Arctic predators and their brown bear cousins (including grizzly bears). They found that over the millennia, polar bears mixed quite a bit with brown bears.
Polar bear fossils are rare and many of the fossils found are relatively young. But scientists got lucky just over a decade ago, when a 130,000 to 115,000-year-old polar bear jawbone… discovered in Spitsbergen†
The recent team produced a new, more complete genome, extracted from that ancient bear’s teeth, and compared it with the genome of 64 modern polar bears and brown bears. Their research is published this week in the Proceedings of the National Academy of Sciences.
“It’s difficult to look at polar bears and polar bear evolution without also looking at brown bears and brown bears because they are so closely related,” said Charlotte Lindqvist, a biologist at the University at Buffalo and lead author of the study. article. a phone call with Gizmodo. “Obviously, they’ve had a fairly intertwined evolutionary histories, mixing their DNA throughout their history after splitting into separate lineages.”
Polar bears and brown bears diverged as species between 1.3 million and 1.6 million years ago, Lindqvist said. Although the two species look very different today, they are crossed after their divergencea process in which more genes from brown bears moved into polar bears, according to the recent research.
In other words, modern polar bears are genetically mixed with brown bears. Previous research even suggests that all living polar bears today descended from a group of brown bears that lived in Ireland and mated with “pure” polar bears during the Pleistocene.
“We see a dominant signal from gene flow going to polar bears, which then suggests that polar bears as a species have inherited DNA from brown bears,” Lindqvist said. “Because they’re such different species — the polar bears are Arctic specialists and the brown bears are more general — you might wonder what impact that might have on the polar bear as a species.”
It’s impossible to say what those ancient polar bears would have looked like without more fossil evidence. Because most animals live and die on ice caps (which have become smaller and completely disappeared in recent years), most ancient polar bear bones are probably at the bottom of the Arctic Ocean.
In the future, the researchers say in the paper, the two species will come into closer contact with each other as sea ice melts due to climate change. These interactions increase the chance of crossings.
In theory, the two species could “melt” in a similar way to how early modern people accommodated Neanderthals in their populations, Lindqvist said, although the bears’ breeding seasons don’t overlap much, and the crossing is a chance encounter rather than a widespread phenomenon. Such events will not save the animals, as habitat loss and other issues related to climate change are likely to counteract any adaptations resulting from the interbreeding of the species. “The pace of environmental change is so fast,” Lindqvist added. “The question is, can they keep up?”
Sex won’t save the polar bear; it is entirely up to humans how much of the apex predators’ habitat remains intact. But by learning more about where these bear species came from and how they interacted in the past, we can guess where the two species are headed.
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