Evolution is a fickle mistress. On the one hand, we can't complain, since humans ended up with opposable thumbs and huge brains (and relatively hairless). On the other hand, we can't fly and our heads hurt if we eat ice cream too fast.

But some of the everyday annoyances that drive us crazy are exactly what made modern humanity possible. For example ...

#5. Getting Kicked in the Junk Hurts Because It Makes Sperm Work Better

As decades of America's Funniest Home Videos have taught us, the only thing funnier than seeing someone else get hit in the junk is a baby who's scared by his own farts. But the hilarious act of hitting a man in the ballsack reminds us of a baffling evolutionary defect -- after all, when's the last time you've seen a shark rolling around on the beach because it got nailed in the balls? And you would have seen it if it'd happened, somebody would have put that shit on YouTube.

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Or maybe one of the more specialized porn sites.

Well, the human crotch has two problems: One, unlike with some animals, the nuts are on the outside of the body. And two, the family jewels are so disproportionately sensitive to pain that just the thought of a wayward hit to the groin will have you doing a crotch block. But why?

It Has to Be That Way Because:

Scientists think a big part of it is the fact that sperm really prefers hanging out at lower body temperatures, and the last time we checked, lower body temperatures are impossible to accomplish from the inside of the body without some kind of weird crotch-mounted air conditioning. So, the sperm has to be suspended in orbs out where the air can get to them (this is why, as we mentioned recently, a laptop can cook a man's sperm to death).

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"It just felt as if my scrotum cried out and then was silenced suddenly."

It's not until you get aroused that things tighten up downstairs, and the best part is that it's actually the woman's (or guy's?) body heat that jump-starts the process that will eventually end with a baby or a mess or both. Because even though sperm production is best at lower temperatures, ejaculation requires some hopped up, crazy-excited spunk. So at the key moment, the testicles retreat, get hot, and you probably know the rest. You also might have figured out that this retreat kind of protects the dangly parts during sex, which is a win-win for everyone.

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Which brings us to extreme ball sensitivity. What's the deal with that? Well, it's not that other animals just love being smacked in the balls, it's that, well, try it. Go find a bull and try to nail it in the nuts with a dodge ball. You can't, can you? Its legs and tail are in the way.

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And with that, a beautiful sport was born.

Humans, however, decided at some point that walking upright would be a great idea, so now we have the perfect storm of external testicles and a posture that literally has us walking balls-first into danger.

#4. We Need Dentists and Braces Because We Evolved Big Brains

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Don't let Hollywood fool you, guys -- most people in this world are sporting teeth that are as crooked as an Illinois governor. If you see someone with a perfect set of chompers, either they or their parents shelled out some dollars to make it happen. The rest of us have more teeth than our little orifices can handle, which is why some of us end up with snaggletooths and fangs and whatever is going on with Steve Buscemi's mouth.

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Complete dental anarchy?

Not to mention the nightmare that is wisdom tooth removal -- those bastards try to cram their way into the jaw so tightly that nothing short of surgery can remove them. Again, it seems like a straight design flaw -- why in the hell would you not have room in your mouth for your own teeth?

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It Has to Be That Way Because:

Before humanity got a taste for flesh, vegetation was our only source of nutrition. But the thing about roots and leaves and nuts is that you need a lot of it to get enough protein to keep on living. So imagine the teeth it would take to grind down that kind of diet all day long. You can go look at a horse, if it helps.

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Oh hey, we loved you in Reservoir Dogs, Mr Buscemi.

Once our big ol' Chiclet teeth had their way with wood pulp or whatever else we were managing to swallow for sustenance, our digestive systems went to work. Digesting all of those twigs and shit sapped whatever energy we had left -- which left zilch for our brains.