You know how you can look back at people living 150 years ago and chuckle at how they thought leeches could cure colds and drills could fix headaches? Well, a hundred years from now, that's how they'll see our treatment of mental illness (assuming they can be so smug living in a nightmarish dystopia). The truth is, we're just barely figuring out why human brains go wrong the way they do, and the most interesting theories suggest that many times what we now call a disorder used to be an awesome advantage.

5 Bipolar Disorder Helped Us Survive the Winter (and Get Laid)

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About 2.6 percent of adult Americans have bipolar disorder, along with its signature manic and depressive episodes that can last for months or even years. It makes you wonder: If it's such a common bug in our 100,000-year-old head computer, how come evolution hasn't gotten around to fixing it by now? Why would natural selection have given us brains that go nuts with activity for a stretch, then just shut down completely?

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And don't even get us started on that appendix bullshit.

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It's almost like some people have brains that are set to hibernate, like bears.

How It May Have Helped Humanity:

Oh, right. It may actually have been a form of hibernation.

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Ask your doctor if Torporine is right for you. May cause drowsiness.

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There is a theory that the brains of our northern ancestors devised a way to oscillate their moods between manic and depressive to align the former with light, warm seasons and the latter with the cold darkness of winter. This would be for the exact same reasons lots of animals do it: The manic episodes turned them into superhunters and uber-gatherers who happily slaughtered and stockpiled while the sun was shining, right up until it was time to sink into wintery depression.

According to this theory, people with bipolar disorder were also masters of boning. Since bipolar disorder is most prevalent in women of reproductive age, some researchers think part of the reason the brains of prehistoric ladies dug bipolarity was sheer procreation: They turned on the manic phase during the summer, when it was most convenient to get pregnant. The subsequent winter down period would have ensured that the lady is less active and free to concentrate on the coming child, which in turn would have led to healthier offspring.