Ask Great Smoky Mountains National Park‘s lead wildlife biologist, Bill Stiver, and he’ll tell you – anything but a black black bear is rare in the Smokies. “Our black bears are true to their name,” he told me back in March from the park. “Cubs are occasionally born with cinnamon or blonde coats here, but it’s a rarity. If you see a bear in the Smokies, chances are it’s going to be black.”
It’s a whole different story out west, however. From Yellowstone National Park out to the Pacific Northwest, the North American black bear is often confused for their brown bear cousin due to – you guessed it – a brown coat. Americans have called this a “cinnamon bear” for centuries. In fact, pioneering explorers like John James Audubon documented them as a separate species altogether. But they’re not, they’re simply black bears (Ursus americanus) with a copper-to-brown coat.
The question of why, though, remains. Why are western black bears born this unique color so often while eastern bears aren’t? Scientists now have the answer.
Western Black Bears are Evolving into Cinnamon Coats
This year, a joint United States and Japan research team analyzed DNA samples from 151 North American black bears from across both the U.S. and Canada. Their findings, published Dec. 16 in Current Biology, were conclusive. Black bears born in western states like Arizona, Idaho, and Nevada are not only far more likely to possess a cinnamon coat than their eastern counterparts, but this coloration is now more common than black among western bears.
The culprit? A mutation called R153C. This mutation appears solely in a gene known as tyrosinase-related protein 1 (TYRP1). It is this gene that causes alteration to the pigmentation of a bear’s coat. In Ursus americanus, this typically results in that famous cinnamon color.
“TYRP1 is a known pigmentation gene in the pathway in the precursor molecules that ultimately produces either eumelanin (black or brown pigment) or pheomelanin (red or yellow pigment),” Emily Puckett, the study’s lead researcher, explains to Live Science. “What it’s doing is changing the amino-acid sequence of that gene.”
Puckett, who’s also an assistant professor in biological sciences at The University of Memphis in Tennessee, says this “cinnamon variant” is “a young mutation,” too. Her team has pinpointed the first mutation causing this coloration as cropping up approx. 9,360 years ago. In the millennium since, it’s slowly spread across the western population.
Why Are We Seeing More Cinnamon Bears?
But this raises as many questions as it answers. Unsuccessful mutations tend to die out, or remain incredibly rare. Take the similar mutations that result in albino, leucistic, or piebald mammals, for example. Each can create a stark white baby, which is far less likely to survive in the wild as they stand out like a sore thumb. Whether predator or prey, being unable to blend into your surroundings is typically a death sentence in kind.
The opposite happens in mutations that aid an animal. Successful mutations typically cause and/or accelerate evolution. Darwin’s finches are the perfect example in which one species of finch branched into dozens, all thanks to mutations that caused different beak shapes. Each shape allowed a finch to excel at consuming different foods. And the more a finch can feed, the more likely it is to breed and create offspring that carry on that same beak-shaping mutation.
So why, again, are more and more black bears turning cinnamon out west? There has to be an advantage.
“Our modeling suggests that yes, [the gene is] adaptive in some way, but we’re not 100% sure what it’s adapted to,” Puckett reveals. “We tested for both thermoregulation and competition with brown bears, and neither were strongly supported. Our new hypothesis is that it’s a mechanism for selective advantage.”
What that selective advantage is (a purposefully-vague term), however, we’ll have to wait and see. Ruling out thermoregulation (the relation of a mammal’s coloration to their ability to regulate their body temperature) is a big step regardless. It’s tempting to think black bears are simply becoming less black in order to absorb less of Western America’s intense heat. But this, as Puckett’s study cites, is not the case.
‘Geography definitely plays a part’
And all the while, eastern black bears remain black. Their cousins of the Great Lakes and Northeast are also less likely to be born cinnamon-coated. For this, Puckett explains the mutation is a “young” one that “hasn’t had enough time for natural migration.”
In short: “Geography definitely plays a part. Our demographic modeling identified that the most likely place where the mutation arose was somewhere in the western region, very likely in the Southwest. From there, it expanded through gene flow throughout populations,” she continues.
In order for eastern black bears to exhibit this coloration on the same scale, a mass migration would have to ensue. Then, cinnamon coats would have to prove an advantage to eastern bears in order to stick around.
But “The bears don’t pass through the Great Plains,” Puckett cites. “If they wanted to go east, they would have to go up north to Canada, across the Canadian [Prairies], around the Great Lakes and then drop back down into the eastern populations. That would take a long time. We do see that it’s happening and is moving [eastward], but it’s a process that takes time.”
Thanks to American conservation efforts, time is something the black bear has. Whether or not our Smoky Mountain bears will take on the cinnamon mutation of their western kin, however, remains a mystery.