that just goes to show how much you can learn from Gallup’s research findings.
Gallup’s approach to studying the design of the human penis is a perfect example of “reverse-engineering” as it’s used in the field of evolutionary psychology. This is a logico-deductive investigative technique for uncovering the adaptive purpose or function of existing (or “extant”) physical traits, psychological processes, or cognitive biases. That is to say, if you start with what you see today—in this case, the oddly shaped penis, with its bulbous glans (the “head” in common parlance), its long, rigid shaft, and the coronal ridge that forms a sort of umbrella-lip between these two parts—and work your way backward regarding how it came to look like that, the reverse-engineer is able to posit a set of function-based hypotheses derived from evolutionary theory. In the present case, we’re talking about penises, but the logic of reverse-engineering can be applied to just about anything organic, from the shape of our incisors, to the opposability of our thumbs, to the arch of our eyebrows. For the evolutionary psychologist, the pressing questions are, essentially, “Why is it like that?” and “What is that for?” The answer isn’t always that it’s a biological adaptation—that it solved some evolutionary problem and
therefore gave our ancestors a competitive edge in terms of their reproductive success. Sometimes a trait is just a “by-product” of other adaptations. Blood isn’t red, for example, because red worked better than green or yellow or blue, but only because it contains the red hemoglobin protein, which happens to be an excellent transporter of oxygen and carbon dioxide. But in the case of the human penis, it appears there’s a genuine adaptive reason that it looks the way it does.
If one were to examine the penis objectively—please don’t do this in a public place or without the other person’s permission—and compare the shape of this organ to the same organ in other species, they’d notice the following uniquely human characteristics. First, despite variation in size between individuals, the erect human penis is especially large compared to that of other primates, measuring on average between five and six inches in length and averaging about five inches in circumference. (Often in my writing I’ll relate the science at hand to my own experiences, but perhaps this particular piece is best written without my normally generous use of anecdotes.) Even the most well-endowed chimpanzee, the species that is our closest living relative, doesn’t come anywhere near this. Rather, even after correcting for overall mass and body size, their penises are about half the size of human penises in both length and circumference. I’m afraid that I’m a more reliable source on this than most. 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 babysat a lascivious young orangutan that liked to insert his penis in just about anything with a hole, which unfortunately one day included my ear.
In addition, only our species has such a distinctive mushroom-capped
glans, which is connected to the shaft by a thin tissue of frenulum (the delicate tab of skin just beneath the urethra). Chimpanzees, gorillas and orangutans have a much less extravagant phallic design, more or less all shaft. It turns out that one of the most significant features of the human penis isn’t so much the glans per se, but rather the coronal ridge it forms underneath. The diameter of the glans where it meets the shaft is wider than the shaft itself. This results in the coronal ridge that runs around the circumference of the shaft—something Gallup, by using the logic of reverse-engineering, believed might be an important evolutionary clue to