Grasping the function of the human penis

Gallup has taken on the task of explaining, in ultimate terms, the evolutionarily designed features of the human penis. He works this as an engineering problem from the perspective of evolutionary psychology, which is always a little bit dangerious, but gallup isn't quite the arm waiver that a lot of other EP's are, so he may be doing it right.

Gallup's work is written up an an all-too-sophomoric Scientific American article by Jesse Bering which just barely falls short of explaining this important biological phenomenon in terms of a pair of headlights, a flashlight, and a little red waagon.

Here's the money quote:

Magnetic imaging studies of heterosexual couples having sex reveal that, during coitus, the typical penis completely expands and occupies the vaginal tract, and with full penetration can even reach the woman's cervix and lift her uterus. This combined with the fact that human ejaculate is expelled with great force and considerable distance (up to two feet if not contained), suggests that men are designed to release sperm into the uppermost portion of the vagina possible. Thus... "A longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity."

The other component of the work is the intriguing possibility that penises have evolved to carry semen previously left in one female's vagina from another male to be deposited hours later in the vagina of a second female. Which I suppose could be called facilitated cuckoldry.

I've not read the original paper yet. I'm not quite up to it. But if I do, I'll let you know if it is truly a seminal work, or if Gallup is just jerking us around.

The writeup is here.

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Since sperm can't survive all that long outside the body, I have to wonder about the "facilitated cuckoldry" explanation. But I can entirely believe that the shape/size of the penis both helps remove competitors' sperm, AND enhances the sexual sensation for both partners. After all, like other apes, we use sex as a social ritual, and our pair bonding is extremely contingent on mutual sexual attraction (especially for the ~80% of our biological history where marriage likely didn't exist).

I subscribe to SciAm's feed so I read this article when it came up. I didn't really think anything of it. It's getting talked about all over the interblag now. I saw a post pop up on Jezebel, a pretty ridiculous site for women, and they seemed almost offended by the piece.

I'm more inclined to believe the shape of the penis evolved to ideally create some sort of plunger/stopper action, another theory I've heard thrown around since this shit blew up. The response on jezebel seems to be that the women think the author is suggesting there is a scientific justification for gang rape or that women are so promiscuous that such a sperm squeegee function is necessary.

No matter what the evolutionary reason for the shape of the penis I'm pretty sure men didn't evolve them to spite us, nor is it absurd to take an academic approach to the topic of reproduction in evolution. No bad ideas in brainstorming, right?

I haven't read the whole piece but I find it an interesting theory that men with a larger penis are more likely to breed. I think this is also evident from how women react to men who have a large penis.

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