Michael: People used to leave trash out for bears on purpose.

From the early 1900s through 1940, trash in California's Yosemite National Park went into a dump. It was surrounded by bleachers and lights so park visitors could come watch the feeding frenzy as 20-30 bears fought each other for a shot at food.

Even after the feeding shows stopped, rangers continued leaving food out in order to attract bears and provide photo opportunities for tourists until the early 1970s. It's entirely possible that bears in Yosemite are still passing down human-food-based foraging behaviors that their ancestors learned more than 100 years ago.

Bears are social learners, and they figure out how to find food from watching their moms foraging while they're young. So if mama bear has learned that humans are a great source of food, she'll teach her cubs that. Then her daughters will teach their cubs, and so on. And even if a bear isn't taught to forage in trash cans, sometimes they just get creative and figure it out for themselves. Which is why we have generations of bears that are more than just occasional consumers of our garbage and have become reliant on human foods.

And it turns out, this wasn't even by accident, because -

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