It’s no secret: We are obsessed with penis and testicle size. Lately, we’re especially fond of evolutionary explanations for why penises and testicles are as large as they are, and why they’re shaped the way they’re shaped. It’s an obsession that extends from the ivory towers of academia on down.
You’ve probably seen the articles by now. They follow a similar pattern in which penis size — often girth, rather than length — is an arms race in which the biggest or most innovatively shaped penis wins the evolutionary prize of passing on its owner’s genes to the next generation. A favorite explanation for the big phallus is female mate choice — that females selectively make babies with males who have larger and, presumably, more pleasurable semen-delivery devices. This is backed up by studies. When life-size projections of naked men are shown to female subjects, for example, those women say they find the ones with bigger ones to be more attractive. (This is exactly how mate choice works where I live; how about you?)
Another explanation is male competition. If you can, ahem, deliver your package to the front yard but the other guy can deliver his to the front door, his is more likely to be carried inside the house first. Or if he can steal away what you just delivered via “semen displacement,” then, again, his package has yours beat. Thanks to his big penis and its fancy countermeasures against other men’s sperm he’s more likely to pass on his winning-penis genes than you are to pass on your loser-penis genes. Loser.
All this is, admittedly, terribly fun to write about, and I’m not even going nuts (gah) like journalists and researchers do in their endless, gleeful coverage of the subject. But some obvious questions are missing from the irresistible headlines: Doesn’t it make sense that for a penis to be useful it has to be somewhat correlated to vagina size? Wouldn’t you explain the size and shape of the key by the size and shape of the lock? So wouldn’t it be a little more scientifically sound to hypothesize that the human penis is sized and shaped like that because it fits well into the human vagina? In short, isn’t it a bit obvious that the privates that fit inside the other privates are probably correlated? Yet even as penis theories fly around, a dime a dozen, we can barely say the word vagina. We seem to only be concerned with the evolutionary trajectory of dicks.
It’s fair to ask, then, how we should be having the conversation about vagina size, especially given science’s (relative) lack of interest in this question and the striking dearth of media coverage devoted to it.
If we were going to answer it the same way we’ve long explained the human penis, and other animal-penis shapes, then it’s clear what approach we’d take. Maybe evolutionary pressures have made the vagina bigger over time because walking upright made the organ more conspicuous and males thought a bigger vagina was better. Or maybe vaginas of a certain size or shape outcompete others at catching sperm. Or maybe it all has more to do with heat dissipation or thermoregulation. But perhaps the strongest candidate to focus on is babies. Namely, the brain and body sizes of newborns, who, after all, have to pass through the organ in question to be born.
In other words, it may be that when it comes to the mystery of how the vagina got to be the size and the shape it is, the answer lies less in all the sweaty speculation and research about women’s orgasms, on their pornographic thoughts and lustful eyes, or men feverishly scooping one another’s sperm out of the mates they’re competing for, and more in women’s decidedly unsexy “birth canal.” But hey, it’s understandable we don’t hear about this as much — we all know that the icky mechanics of birth are a lot less fun to talk about (and frankly get fewer clicks) than the mechanics of sex. I was actually only able to find one vagina-size-based, childbirth-based explanation for human pieces — a 2008 article by Dr. Edwin Bowman in the Archives of Sexual Behavior. Naturally, it ends with some masculine self-congratulation: “In sum, man’s larger penis is a consequence of his larger brain.”
The point is, the literature rages on with all of these different creative explanations for penises, with nary a vagina in sight. But you heard it here, at least: Childbirth has likely had a huge impact on the evolution of the human vagina — and, consequently, the penis. And yet, for whatever reason, we continue to put the penis on a pedestal, severed from its full evolutionary context.
Holly Dunsworth is an assistant professor of anthropology at the University of Rhode Island. This article was adapted from a post on evolution-institute.org.