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The 5 Weirdest Reasons We Have Sex (According to Science)

Ever since Darwin popped off his big theory of evolution, we've all kind of presumed that everything we do -- the way we eat, the mates we choose, the way we purposely mispronounce "indubitably" for laughs, everything -- is ultimately tied to one goal: continuing the species. But sometimes getting from A to Baby isn't as intuitive as you'd think. And scientists have had a hell of a time figuring out why.

Now, we're not saying that these theories behind our sexual behaviors are the gospel truth or that there aren't other, conflicting theories out there. But if they are true, sex is even weirder than we thought.

#5. Kissing Evolved as Virus Protection

Long before you tasted the wonders of sex or the body parts that have to do with sex, you (hopefully) tasted the inside of another person's mouth (if not, you should probably get off Cracked and finish your pre-algebra homework, sonny). But have you ever stopped in the middle of a deep kiss and said, "Wait a second, why the hell are we doing this?"

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"OK, now I just consume your head whole, right?"

Pretty much all human cultures have kissing, and a few other animals do it as well. But why? Why are we cramming our mouths together? Why don't we nuzzle noses or tap kneecaps? Why don't we butt rub?

The Theory:

Researchers at the University of Leeds have hypothesized that kissing evolved as a way for women to expose themselves to an infection called cytomegalovirus. Never heard of it? Maybe you've heard of its family -- herpesviruses (we're not missing a space between "herpes" and "viruses" -- that's the actual name of the family). The thing about this particular virus is that, much like a Looney Tunes tramp stamp, you don't know if your partner has it until it's too late. By then you've already exposed yourself to something you'll never shake.

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The tattoo equivalent of mustache crabs.

And that's bad news for the species -- if a woman develops the active cytomegalovirus while pregnant, there's a 50 percent chance she won't carry the baby to term. But, if she gets exposed in incremental bits in the months leading up to her pregnancy, she can be inoculated from a full-on primary infection. Think of it this way: The virus is kind of like early 2000s boy band music. In small doses, it's not so bad. In large doses, it will abort your baby.

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"Hey hon, run up the stairs! You've got to hear this 'N Sync album."

You can see where we're going with this -- the easiest way to transmit the virus is through swapping saliva. The theory is that, rather than moving straight into intercourse (which could immediately get a woman pregnant while giving her mega-herpes and maybe killing her unborn child), females created this courtship-slash-inoculation period -- the kissing season. Which is a way better and less gross theory than the first draft -- that kissing evolved as a natural result of mothers prechewing food for their young (and lovers).

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"BLARRRRGHIloveyousomuchAAARGHULLBRR."

#4. Women Have Boobs So Babies Don't Suffocate

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Stick this in your lip and chew it: Human breasts are 100 percent unique. If you were into animals in a sexual way, you wouldn't be able to find any with boobs unless they were lactating -- only human women don't go back to flat-chestedness when they're off milk duty. True, gravity and age will eventually take their toll, but barring disease or a tragic mammogram/waffle iron mix-up, a woman's breasts are there to stay.

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Don't just stand there, get some maple syrup on them! And maybe some jelly!

So the question is why? Why were humans, more than any other mammal, bestowed the bosom blessing?

The Theory:

Boobs are designed so babies don't suffocate and die while nursing. Take a look at this face:

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This easily killable face.

OK, now look at this totally not adorably pathetic photo of a baby monkey:

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If he was sucking his thumb this would be too adorable to legally post.

Notice the difference? Look closer. It's the mouths. Most mammals have protruding snouts that jut out like tobacco-dipping animal hillbillies. They were made that way. Humans, not so much. Try this little experiment: Staple a rubber nipple to a wall and try to suck it. It doesn't work, does it? Not just because you're suckling a wall, but because your nose is smooshed against a flat surface.

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"Oh please God, I haven't had sex in three years."

Hurry, back up, before you die! So the theory is that as humans evolved flatter faces to offset our huge brains during labor, women evolved bigger bosoms to reach their babies' little tiny mouths. Lucky for humanity that women hate it when their babies suffocate. That's literally the worst.

#3. Moaning Was an Invitation to Group Sex

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Quick question: Who makes more noise in bed, men or women? Believe it or not, there haven't actually been many studies on the subject, so you should probably just rely on anecdotal evidence. Who do you hear more in hotels? Who is louder in your own bed? Which grandparent can you hear from across the house?

It's the woman, of course. With the guys, it's usually a few little grunts and squawks of exhaustion, while women are the ones you usually hear making full-throated sex noises and appeals to a deity.

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"Ph'nglui mglw'nafh Cthulhu R'lyeh wgah -- ow, Jesus, not so damn hard."

Of course, the frequency and loudness and squeakiness of sex noises vary from culture to culture, but we do know that there are other primate females who also make noises during sex (we're looking at you, slutty bonobos). And we also know that at least some of the noises gushing from the woman's mouth have nothing to do with orgasms.

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We have a feeling most monkey sex has nothing to do with female orgasms.

It seems like there's another reason here that we're missing. Authors Cacilda Jetha and Christopher Ryan think that it has to do with promiscuity.

The Theory:

In their 2010 book, Sex at Dawn, Jetha and Ryan put together a startling theory -- that humans aren't meant to be monogamous, that we were never meant to be monogamous and that biology itself is what's tearing modern marriages apart. And among the justifications for their theory, Jetha and Ryan cite female copulatory noises.

ideacityonline
"Our work began as a scientific explanation for David Duchovny."

Remember how we mentioned female bonobos like to make lots of noises when having sex? The funny thing about this is that bonobos are just as related to humans as chimps, and they do a lot of the same stuff that we do sexually, like French kissing and oral sex and face-to-face intercourse.

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Hamsters and armadillos share the same boat. The vanilla, missionary, 20 years of marriage boat.

They're also not monogamous, not by a long shot. And here's where it gets interesting: When female bonobos are screwing around, they make lots of noises, not because they're having a good time, but so the other males in the vicinity will hear them. It's a mating call. An invitation. An alert to the other boys in the area that it's party time and she's open for business.

Now, if bonobos are in the top two of our closest relatives, and they totally are, and they've never bought into this whole one man, one woman business, does that mean we should all try to Gingrich our marriages? Probably not. But you definitely should make sure the neighbors aren't around the next time you and your lady get it on.

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"Come on, you dicks, evolution says I'm invited."

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