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.

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We imagine that's it's a rather nasty shock to suddenly wake up with a several-month-old infant latched onto you.

Bipolar disorder might also have been helpful as a method of sexual seduction, as affected people are drawn to artistic endeavors such as music, which, as every single rock star on Earth will tell you, doesn't exactly decrease your chances with the opposite sex. Thus, prehistoric people with bipolar disorder would have reproduced like rabbits, which helped preserve their lineage and pass along their genes.

Which is too bad, really, because humanity might have been eaten by horrorwolves a long time ago if it wasn't for old OCD.

How It May Have Helped Humanity:

To put it simply, the kind of obsessive attention to organization and cleaning rituals that makes somebody a neurotic mess today may have been the difference between life and death for our ancestors.

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With that many ass-scratches in a civilization without toilet paper, you're bound to get something on your hand.

This is another case where you have to get some perspective on just how radically different the world was then. It doesn't exactly take a huge amount of mental effort to stay alive through an average Saturday of eating Cheetos and watching 12 hours of terrible direct-to-Netflix action movies, but evolution built a brain that was designed to handle a way more dangerous world. An OCD sufferer is acting like he'll die if he doesn't get every little thing in his immediate surroundings exactly right, but you don't have to go back too far in your time machine to find a world where that was absolutely true. It is thought that the condition originated as an evolutionary warning system that kept our whole species alive by making certain early humans constantly worried about everyday stuff like "Is this thing still good to eat?" "What's that approaching noise behind the woods?" and "Is Grog being carried away by that giant bird?"

As we took up agriculture and started giving up our hunting and gathering activities, we stopped using a lot of those involuntary mechanisms we had developed to dodge the various members of the animal kingdom that either saw us as food or objected to being poked with a spear. But those who kept their compulsive behaviors still had a place -- people who have OCD, for instance, get disgusted more easily, which may have originally served as a means to get them to stay away from icky things that pose a potential danger in the form of bacteria and parasites ... which in turn led to inventions such as basic hygiene.

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"Yeah, I'm gonna stick my hands in boiled fat and lye. Good thinking, idiot. Pass me some more dirt."

This constant on-the-edge behavior may or may not have been frowned upon by the rest of the community, but ultimately it worked to teach everyone the essential skills of staying alive. After all, no matter how annoying the dude who insists there's a bear in the area might be, people start paying attention to him by the time the sixth guy disappears to the sound of a loud growl and a baritone burp.

Also, because everyone was hunting for survival, not giving a shit about routine would have led them into exploring more and eventually finding the place with the best view and greenest pastures. Then, just as now, great advancement happened because capable people got bored with the status quo.

This theory is backed up by the fact that the gene associated with ADHD is common among particularly plucky and adventurous native populations. Studies have also shown that hunter-gatherers with ADHD are able to keep themselves better nourished than other people, providing them with an edge over other, less adventurous souls.

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Even if they do annoy the piss out of everyone else.

Sadly, our current way of life doesn't require much exploration, so the 11 percent of children still diagnosed with this survival supertalent are left fidgeting and staring longingly out of the window while waiting for their medication to kick in.

For these people, all sorts of mindless, everyday things you take for granted, from reading menus to browsing the Internet, become laborious chores. Luckily, most sufferers can eventually overcome the condition and excel. Or rather, turn their back on their evolutionary excellence.

How It May Have Helped Humanity:

When you look at the stats, something strange starts to jump out: According to some surveys, over 30 percent of entrepreneurs describe themselves as dyslexic, and tons of influential people -- from Albert Einstein to Steven Spielberg -- have struggled with the condition. People with dyslexia tend to be highly creative, artistic, and intelligent, and often kick ass at solving multidimensional problems.

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Things become trickier when it comes time to write the answer down.

Dr. Duncan Milne, a big name in the field of neuropsychology, says that this is not a coincidence; according to him, dyslexia is a telltale sign of exceptional brain badassitude. During our hunter-gatherer period over 200,000 years ago, there was no reading or writing; we were too busy wrestling bears and figuring out which mushrooms are edible and which ones make you visit the pink pumpkin god. Our life was all about clever ideas, efficient communication, and creative problem solving, which you may recognize as the exact damn things dyslexics tend to excel at.

When the kind of brain that is particularly talented in the important act of staying alive in the most efficient way possible is suddenly facing reading and writing -- two fairly recent inventions that radically differ from the frantic survival shit it's spent countless millennia specializing in -- it tends to view them as unnatural acts. A dyslexic brain is not stupid or even malfunctioning -- it's just wondering why it has to make sense of all these stupid squiggles when it could be out punching tigers instead.

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Billy may have a reading disability, but he's already surviving at a Bear Grylls level.

Yes, according to this theory, dyslexia is really not a disorder at all: It was always there for the exceptional individuals whose brains had an extra edge. We just never realized it, so when someone came up with all that "reading" and "writing" poppycock, the people whose brains dared to object were looking at a ticket to Disorderville.