Objectively, even big human penises are small, other than in comparison with other human penises; but virtually all human penises are big in comparison with those of the other 192 primate species. Flaccid, the penis of the gorilla and the orangutan, both with much bigger bodies, is virtually invisible; erect, it reaches 1.5 inches or less; the chimpanzee, man’s closest relative (sharing 98 percent of his DNA) achieves an erection twice that of the other two apes but still only one-half the average human one. Why, comparatively, man’s penis is so disproportionately large is a question that engages a clutch of disciplines including archaeology, anthropology, and zoology, as well as the evolutionary, psychological, and sociological branches of biology. Collectively they remain at a loss to provide what is known as “ultimate causal explanation.”
The consensual “ological” view is that when man’s hominoid ancestors came down from the trees 4 million years ago, their penises were of a size with the apes—“vanishingly small,” according to archaeologist Timothy Taylor in The Prehistory of Sex. Then, however, when upright walking swivelled the sexual focus from rear to front of both sexes, a focus that was intensified by the loss of the majority of bodily hair other than in the genital area, the penis began the process of “runaway selection.”
Feminists incline to the view that it happened because females wanted it that way; that when femina became erecta, the angle of the vagina swung forward and down, moving deeper into the body, obliging the penis, as Rosalind Miles put it in The Women’s History of the World, to follow the same principle as the giraffe’s neck: “it grew in order to get to something it could not otherwise reach.” On the other hand, the big penis may have evolved because that’s what possessors wanted—a greater attractant to potential mates and a more visible means of warning off rivals. A big penis also increased the male’s chance of inseminating a female who was having sex with other males, by getting closer to the cervix. There are objections to such theories—not least that other primate males have continued to propagate their species with considerably less at their disposal. As to the theory that the penis grew to assist humankind’s imaginative variety of sexual positions, orangutans and chimpanzees, particularly the pygmy chimpanzee or bonobo (a separate species, found in the Congo, which has a more upright gait and a more “human” skeleton), are equally imaginative in their coupling—and they can do it swinging from trees while man only talks about doing it swinging from chandeliers.
But if science cannot say definitively why man’s penis is so big, it does have an explanation as to why his testicles are the size that they are.
In the early 1980s the evolutionary psychologist David Buss caused widespread excitement among the “ologies” with the hypothesis (in The Evolution of Desire) that the more promiscuous a primate species, the larger the testicles of the males belonging to it—penis size, he surmised, was less relevant in achieving impregnation of a female having sex in rapid sequence with other males than being able to produce the most copious and frequent ejaculate. Subsequently, British scientists weighed the testes of 33 primate species, including man, to assess the testicle-promiscuity link. Interestingly, by this measure, the human male, the primate with the biggest penis, was not the king of the swingers: His testicles, together weighing 1.5 ounces, bore no comparison with those of the chimpanzee, which weighed an astounding 4 ounces, a three-times higher testes-to-body-weight ratio than humans. And the mighty gorilla, the primate with the smallest penis? Again he trailed the field, his testicles little more than one-half the weight of man’s. As Buss pointed out, the gorilla, with his monogamous harem of three to six females, faces no “sperm competition” from other males. On the other hand, the promiscuous common chimp has sex almost daily with different females and the even more promiscuous bonobo has sex several times a day.
Somewhere between gorilla and chimp comes man, neither entirely promiscuous nor entirely monogamous, his penis evolved far beyond those of his distant ancestors but his testicles or at least their firepower probably reduced— his sperm production per gram of tissue is considerably less than either chimps or gorillas, leading to the “ological” view that, as expressed by Lynn Margulis and Dorion Sagan in Mystery Dance: On the Evolution of Human Sexuality, he once, when the business of insemination was a contest, had a bigger “testicular engine.”
Excerpted from God’s Doodle: The Life and Times of the Penis by Tom Hickman, out now from Soft Skull Press.