Could cave women be responsible for today’s relatively large penises?
by Tara Haelle
“The upright body posture and protruding, nonretractable genitalia of male humans make the penis particularly conspicuous even when flaccid,” four Australian researchers note in a new (seminal?) study. No one can argue with that. The question is, did cave women care?
It’s the question that never goes away, whether asked in sincerity or in jest. How much does penis size matter to women? After all, as the four (all male) researchers of this paper observe in the Proceedings of the National Academy of Sciences, “novels, magazines, and popular articles often allude to the existence of a relationship between penis size and sexual attractiveness and masculinity.” That’s putting it mildly.
Various scientific studies have done qualitative research on this question, asking women outright or having them judge photographs. Of course, hand-held photos may not adequately convey the true size of a penis, and we can all imagine how problematic just asking women might be for scientifically reliable responses. (Past studies have found women prefer longer penises or wider penises or claim that size is unimportant.) Therefore, the results to date have come up short in addressing this question from an evolutionary perspective: could female mate choice “have played a role in the evolution of the relatively large human male penis?” (Compared to other animals, humans tend to be proportionally well-endowed.)
I can’t deny I had fun reading this study and contemplating the points the researchers, um, raised. The researchers note in their abstract, “Before clothing, the nonretractable human penis would have been conspicuous to potential mates.” Ya think? I think of the times I’ve wished a man would look at my face instead of a foot below it, and I wonder if men once had that problem with women’s roving eyes as well. Given that one estimate puts the development of clothing at 170,000 years ago, that certainly leaves plenty of time before the loin cloth for women’s preferences to influence the evolutionary course of the penis. (Oh, the power cave women might have… wielded!)
Scientists already know a little about how women choose mates, including the fact that they take multiple cues into account. We know height and shoulder-to-hip ratio influence men’s attractiveness, but also that a woman’s preference for a man’s physical traits depends in part on her own physical traits (taller women like taller men, for example). In assessing attractiveness of penis size, there are two other factors to consider. One, the appearance of size may relate comparatively to other traits (the same size penis looks bigger on a shorter than on a taller man). Two, a man’s penis size may be related to other genetic factors that influence women’s preference, independent of the penis characteristics.
Since we cannot hop in a time machine to do research on ancient humans ourselves, the researchers tried the next best thing: tap into women’s innate preferences using a series of life-size computer-generated men with varying physical characteristics. Using survey data to come up with averages for each trait, the researchers created figures that varied in penis size (5-13 cm flaccid), height (1.63-1.87 m, or about 5’4″ in to 6’2″), and shoulder-to-hip ratio by seven measurements each: three in the average range and then two standard deviations in either direction. Matching each variable with every other led to 343 figures.
The researchers recruited 105 heterosexual Australian women, average age 26 and predominantly of European descent, to view each image at life-size on a screen and rate the figure’s attractiveness on a scale of 1 to 7. Standing about 20 feet from a wall where the life-size virtual men were projected, the women each viewed 53 figures, including four control figures where all three characteristics were an average size. They took about three seconds to rate each figure in terms of its sexual attractiveness, though the women tended to linger a second longer on the ones they ended up rating as more attractive.
And the results? Drumroll please… Folks, size does matter. “Our results directly contradict claims that penis size is unimportant to most females.” However, don’t let those findings rub you the wrong way. It doesn’t matter as much as you think. Although the women preferred taller men with more “masculine” (greater shoulder-to-hip ratios) figures and larger penises, height and penis size were far less influential to the women’s choices, and the point of diminishing returns arrived at a penis size already slightly below average — 7.6 cm (just under 3 inches) while flaccid. In other words, starting at 7.6 cm long, each additional increase in attractiveness for a larger penis drops off.
The attractiveness rating did keep going up slightly, however, to the extent that “any potential peak (i.e., the most attractive penis size) appears to fall outside the range used in our study.” (Perhaps they should have tossed a few Dirk Diggler silhouettes in there just to test women’s upper threshold.) But the important thing is shorter men or those with smaller penises weren’t getting, well, shafted.
Meanwhile, shoulder-to-hip ratio accounted for about 80 percent of the variation in the women’s ratings. When height and penis size were added to the model, each had almost the same impact: height explained about 6 percent of total variation in attractiveness and penis size about 5 percent. So penis size may have meant as much as height to the cave woman. What we don’t know is how much it might matter to women today, partly because of cultural influences and partly because men don’t tend to walk around in public wearing these.
Some of the more interesting findings were how different traits of both the male figures and the women raters interacted. As past research has already shown, taller women preferred taller men. But the larger penis size also mattered more on the taller men, for which the researchers offered two possible explanations: “This result could be because perceived penis size was smaller when assessed relative to the height of a taller man; or because of general discrimination against short men irrespective of the value of other traits, so that even a larger penis did little to increase their net attractiveness.” There was also weak evidence that heavier women preferred bigger penises, though a few outliers made it difficult to tease out the reliability of this effect. (I’m a heavier female, actually, but I’m married, so I plead the Fifth.)
What’s also unclear is why women might prefer a larger penis (again, keeping in mind that the point at which “larger” was most important in this study was for a size still below an average man’s size today). The preference could be cultural, could be an innate aesthetic preference, or could relate to the idea that a bigger penis means a bigger orgasm (whether based on assumption or experience). Regardless, the penis appears to be low on the scale of what matters to women physically, even if it does matter a little. And in the age of clothing, women are generally (one hopes) more likely to learn a bit about a man’s personality and other traits before she gets a good look at his jewels. Bottom line: a typical guy today is unlikely to be penalized for his penile size.
Feature photo of Cappadocia, Turkey by Jean-Marie Hullot. Thumbnail image by Tara Haelle.