Grizzly bears and polar bears aren't one species—but they share a close ancient history.
Karsten Sund, Natural History Museum , University of OsloThe longer you think about polar bears, the stranger they seem. They’re the largest bears and the largest land predator. They’re adapted to a life spent crossing open ice floes, or waiting out hungry summer months. Despite those superlatives, it’s hard to figure out how exactly these bears came to be, because they rarely leave bones behind to be studied.
The study also clarifies a yearslong debate among evolutionary biologists: Polar bears and brown bears are so closely related that it’s been proposed the animals should be lumped together as one species. According to the new analysis, which compared the DNA of the ancient jawbone to that of 65 modern bears, the species are clearly genetically distinct.
But the two have evolved in tandem for roughly the past million years, and polar bears carry genes from repeated interbreeding with brown bears. That’s a new discovery—prior studies, which hadn’t had access to the ancient jawbone, had suspected that polar bears had contributed genes to brown bears. In fact, it’s the other way around.expand across the high Arctic as brown bears move north into polar bear habitat.
Brown bears are wildly genetically diverse compared to their maritime cousins. There are the populations Americans know as grizzly bears, which inhabit the Rocky Mountains and once lived as far south as Mexico. There are European brown bears in Scandinavia and Russia. There are Kodiak bears, which live on the Alaskan Kodiak Archipelago, and grow nearly twice the size of typical brown bears, rivaling the size of a bison.Once, polar bears were genetically diverse, too.
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