An Evolutionary Look at Penis (and Testicle) Size

MANCHESTER, U.K.—Carole Jahme, an evolutionary psychologist who writes a column for the Guardian, weighed in last week on why human beings have relatively larger penises (and smaller testicles) than their primate cousins and why size still matters to women. In a nutshell, so to speak, the answer to the above is “female mate choice.”

Jahme’s post was in response to the following question from a reader:

Dear Carol, Why are women so obsessed with the size of a man's cock – wanting ones 6 inches and over and kicking others aside when they really should be concentrating on the emotional connection and love being shared, putting the size of the man's cock right out of her mind?”

Jahme’s answer went into greater evolutionary detail than the reader may have expected. “Female primates,” she wrote, “can experience multiple orgasms, and it has been theorized that ancestral hominid females sought out males who would sexually satisfy them. Through the mechanism of sexual selection, this will have increased penis size and altered structure.”

Today, wrote Jahme, the average erect gorilla penis is 1.25 inches long, the average chimp or bonobo penis is about 3.15 inches, and the average human penis stands erect at about 5.1 inches. Most primates, she adds, have a penis bone called a baculum, and achieve erections through muscle contractions. The human penis, on the other hand, evolved a system of vasocongestion (i.e., the swelling of bodily tissues caused by increased vascular blood flow and a localized increase in blood pressure) to achieve erection, with the result that an erect organ is far more flexible than that of other primates.

“This unique adaptation is thought to have been selected through female mate choice, and by the time Homo erectus arrived on the scene, the hominid penis was significantly longer, fatter and more bendy than our ape cousins’,” wrote Jahme. “It has even been theorized that bipedalism evolved in humans to allow the fashionably new, larger, flexible penis to be displayed to discerning females.”

That explains the human primate’s larger, more flexible penis, but what about his testicles? According to Jahme, “As a proportion of overall body size, chimp and bonobo testes are twice as large as human testes, whereas gorilla testes are half the size.”

The answer, she says, has everything to do with the correlations between primate mating patters and male genital anatomy. In short (hehe), chimps and bonobos exist in multi-male/multi-female groups, in which females mate with several different indivuduals, meaning that males “must reproductively compete in this way and larger testes will therefore confer greater reproductive fitness.”

Female gorillas, however, live in harems and don’t have as much choice, resulting in males with smaller penises and testes than other primates but larger canines and biceps to warn or fight off competitors.

Early hominid group dynamics were likely more akin to the bonobos, Jahme notes. “Ancestral females would have experienced a sexual freedom denied in Western cultures today and it has been suggested that our ancestors went through a period of matriarchy and enhanced female choice,” she wrote.

This brings us to the original question of why women continue to be obsessed with size. According to Jahme, the answer to that age-old question has never changed: they simply can’t help themselves.

“Women are as aware as men that to build a stable relationship you need trust, shared interests and the ability to keep each other amused,” she wrote. “But a woman is not going to ‘put the size of a man's cock right out of her mind,’ because she can't. Females have an evolved interest in the size of a man's penis, which has been sexually selected for its size and shape.

“But humans are also selected for creativity,” she adds. “We are highly innovative, imaginative apes. Accordingly, women's minds can be aroused by creativity and being sexually imaginative can be physically arousing, adding satisfying metaphorical inches to one's love life.”

Does any of this have anything to do with porn? It does, but only to the extent to which porn portrays penises as larger than the human average—with its direct correlation to female sexual satisfaction—and the not unrelated extent to which young males (and females) use adult entertainment to assess the adequacy of their own (or their mates’) genitalia. Because the number of human males with penises over seven inches in length declines precipitously, anything beyond that length is outside the evolutionary preference of from 5.5 to 6.5 inches. That average is not by accident; anything over could tend to cause more pain than pleasure.

In other words, monster cocks may attract certain size queens, but as far as the survival of the species is concerned, too much of that sort of friction could spell doom for the human race.