There are so many unintentionally hilarious "parts" in this Scientific American feature about penis shape, starting with the entire premise.
Jesse Bering writes: "If you've ever had a good, long look at the human phallus, whether yours or someone else's, you've probably scratched your head over such a peculiarly shaped device." I don't have one, but the form of a penis doesn't puzzle me at all; isn't it designed to fit inside of a vagina? Isn't that how nature works? Bering's piece is filled with lots of "heh" moments, like "the human penis is actually an impressive 'tool' in the truest sense of the word" and "If one were to examine the penis objectively-please don't do this in a public place or without the other person's permission…" Oh, LOL, dude. Ha.
He also takes special care to note that human penises are not like ape penises:
Having spent the first five years of my academic life studying great ape social cognition, I've seen more simian penises than I care to mention. I once spent a summer with a 450-pound silverback gorilla that was hung like a wasp (great guy, though) and baby-sat a lascivious young orangutan that liked to insert his penis in just about anything with a hole, which unfortunately one day included my ear.
Anyway, here is the ground-breaking information discovered about the shape of the human penis:
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.
You don't say!
But there's also something called a "semen displacement theory," which likewise relates to how the penis is shaped:
Since sperm cells can survive in a woman's cervical mucus for up to several days, this means that if she has more than one male sexual partner over this period of time, say within 48 hours, then the sperm of these two men are competing for reproductive access to her ovum. According to [researchers] Gallup and Burch, "examples include, group sex, gang rape, promiscuity, prostitution, and resident male insistence on sex in response to suspected infidelity." The authors also cite the well-documented cases of human heteroparity, where "fraternal twins" are in fact sired by two different fathers who had sex with the mother within close succession to each other, as evidence of such sexual inclinations.
So: The penis is "sculpted" in such a way — it has a head, unlike many penises in the animal kingdom — so that it displaces the semen of competitors from the vagina. [Does anyone remember when 'Harper's' magazine used to advertise a 'Penises of the Animal Kingdom" lithograph in its classified ad section? -Ed.]
It sounds crazy, but the theory has been "proved." How did the scientists do that? It the most scientific way possible:
The researchers selected several sets of prosthetic genitals from erotic novelty stores, including a realistic latex vagina sold as a masturbation pal for lonely straight men and tied off at one end to prevent leakage, and three artificial phalluses.
Yeah, but what about the semen?
The authors borrowed a recipe for simulated semen from another evolutionary psychologist, Todd Shackleford from Florida Atlantic University, and created several batches of seminal fluid. The recipe "consisted of .08 cups of sifted, white, unbleached flour mixed with 1.06 cups of water. This mixture was brought to a boil, simmered for 15 minutes while being stirred, and allowed to cool."
Seriously. They cooked jizz. Then the scientists inserted the phalluses into the faux vag at varying depths and measured semen displacement and found that a phallus with a head did a better job than one without. In addition, according to a separate study, "penile behavior" shows that "in the wake of allegations of female cheating, men thrust deeper and faster." To get the other dude's semen out!
Lastly, Bering explains how a woman can get pregnant by a man she never had sex with:
If "Josh" were to have sex with "Kate" who recently had sex with "Mike," in the process of thrusting his penis back and forth in her vagina, some of Mike's semen would be forced under Josh's frenulum… Were Josh to then have sex with "Amy" several hours later, it is possible that some of the displaced semen from Mike would still be present under his foreskin and thus may be unwittingly transmitted to Amy who, in turn, could then be impregnated by Mike's sperm.
Of course, all of these people would need to be obsessed with dick, like Bering, the author of this article, who, by the by, admits that he is gay.
Secrets of the Phallus: Why is The Penis Shaped Like That? [Scientific American]
Related: Grasping The Function Of The Human Penis [Greg Laden's Blog]