Q: Genetically, it seems that grizzlies and black bears are pretty closely related. So why is your behavior so different? —Bear-Curious, via email
A: I'm glad you asked that, Bear-Curious—most people just want to know whether I'll eat their trail mix or not (the answer is yes, happily, if you let me). But to answer your question, it all boils down to evolution.
Grizzly or brown bears are relative newcomers to North America—we only showed up 50,000-13,000 years ago, around the time you people showed up. Black Bears, meanwhile, have been around for about a million years. They evolved in mixed forests and floodplains near trees, which helps explain their relative timidity. Adept tree climbers, they've learned to avoid confrontation and threats by scampering up trees or fleeing the scene with relative speed. A dense forest ensures plenty of options for escape and hiding.
Grizzlies, however, likely evolved on tundra, high plains, and open forests where they lack sufficient places to hide or escape. Their relatively large size also prevents them from effectively climbing trees as a regular strategy for survival (though we can do it). Because of this, some scientists theorize that we had to develop more aggressive behaviors to defend ourselves, our food sources, and our young. (Crazy fact: Some brown bears endemic to thick European forests behave much more like black bears than the grizzlies of North America).
Brown bears don't live on the plains (for the most part) anymore, but we drove them back to limited mountain enclaves in only about 70 years. This is much faster than any form of adjustment in evolution could keep up with, so we still exhibit the aggressive style learned out on the plains over millions of years.
You humans haven't always been the best neighbors, and widespread extirpation pushed grizzlies down to about 1 percent of their former range. On the other hand, much more adaptable black bears still inhabit much of their former range. In recent years, you've decided to be a little more neighborly, with mixed results. I know I'm not the type of neighbor to bring over a casserole, but let's keep trying to get along, shall we?
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