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Evolution Explains Why We Still Have Butt Hair

It’s certainly not sexy, so why would we evolve ugly crack hair?

by Derek Mead
Sep 22 2011, 7:58pm

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Welcome to Evolution Explains, Motherboard's weekly investigation into the human-animal (humanimal?) condition through the powerful scientific lenses of ecology and evolution. Don't say you didn't learn something. Now get to readin' already.

After last week's discussion on dogs eating feces, a random Internet friend surprised me with an emailed question:

Hello Derek. Bev here. First time, long time. I'm 99.999999999999999999999999% sold on evolution, but then I think about how we still grow hair in our ass crack. The fuck's up with that? I'ma hang up and listen now. Thanks!

You know, that's actually a pretty good question. Why do we have ass hair? It's certainly not sexy, so why would we evolve ugly crack hair? Hell, according to non-bear porn, we shouldn't have any hair below our necks. So if the whole point of evolving is to make more copies of yourself, which in some sense requires you to more effectively get laid, what's the deal with all unseemly perineum hair (and other ugly stuff) that just won't go away?

There are a whole lot of issues in play here, but let's focus on just a pair: the difference between trends or preferences and actual selection pressures, and the ability of animals and us to cheat those pressures.

For a specific trait to evolve throughout a population, there must be some kind of sorting process to weed out the other options. Those forces could be environmental, like the Sherpa's increased ability to absorb oxygen that is a necessity in their high-altitude home, or sexual, like how some female birds only mate with the males who have the most perfectly elaborate dances.

Let's be honest here: one person's shaved balls is another person's bushy mons pubis. That is to say, having a hairy butt crack isn't necessarily unattractive. Some people love it. And since some people love hairy butts, hairy butt genes persist in humans because people with hairy butts are getting laid. Hell, in some circles, they're getting laid a lot. Hairy butt cracks stick around because at the very least, because they aren't a guaranteed deal-breaker, hairy butt genes keep getting passed on.

In terms of what's attractive, our opinions change all the time. One year butt hair may be in, another it's out. Fat used to be gorgeous, then it was heroin chic, now it's somewhere in the middle. Evolutionarily, hairy butts are far different than human traits that have diversified to deal with specific environmental pressures. That's simply because butt hair doesn't exert such a strong selective pressure that it forces humans to evolve to deal with it.

As a more basic example, take skin color. Throughout history—with worldwide migration so simple now, things are different—people near the equator tended to have darker skin than those farther away largely because the sun is stronger at those latitudes. That simple fact hasn't ever changed and over time humans evolved to deal with it.

Now let's use me as an example. I'm very fair skinned and I've got a hairy butt. If I'd been born in, say, the African savannah in pre-sunblock times, I'd have been dead from sunburn before I ever got old enough to have kids, which means my pale genes would have been dead in their tracks. My ass hair doesn't present the same issues: it's not inherently detrimental to my survival, which means it's not preventing me from living long enough to make little versions of me. Therefore, the butt hair genes live on.

Of course, humans have the curious ability to create artificial selection pressures; in other words, we've figured out how to game the genetic oddsmakers. Look at the breeding of domestic animals, like show cats.

There are all of these different specialized breeds of fancy cats because people decided the specific traits they wanted in those cats and bred them to be that way. For example, if you keep breeding longhaired cats with other longhaired cats, genetic odds say you'll eventually end up with a breed of very hairy cats. But start letting all the longhairs bang the short hairs and all the Siamese screw the Burmese and everything becomes a mishmash again.

Because hairy butts are pretty pervasive throughout the seven billion-strong pool of human genes, and because there isn't any distinct pressure against hairy butts, they're never going away, barring some horrific world dictator's anti-asshair regime.

Yet interestingly, even given a global hatred for wiry derrieres, they won't go away because those so endowed can still fake smooth bottoms. Being able to cheat the system, to avoid selection pressure by shaving your butt, works in the same way people haven't evolved to have natural face makeup. Even if a certain makeup look was the only look considered desirable, the world's population won't evolve towards that look because even those who don't have those genes can still fake it.

It's the reason fake boobs work. There's no major 'only natural boobs' lobby; a large number of dudes and dudettes simply like big boobs and don't care a lick whether or not a woman's (or man's) giant rack is cheating or not. This type of cheating and scamming is massively popular throughout the animal world, and there is a wealth of social animal behavior research studying just how populations police against those cheats.

But in the very end, that type of policing, or self-regulation, doesn't really affect butt hair. I mean, as you're deep in the throes of passion with someone you love or simply want to get frisky with, are you really going to say "Wait! Is that some ass stubble? Are you an ass shaver?" and kick them out of your bed? Hell no. Just as most people don't find beards, red hair, brown eyes or differing heights an impediment to getting busy, rump fuzz isn't preventing any pregnancies. And that's why, year after year, ass hair abides.

Previously Evolution Explained
Why Dogs Eat Poop

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