does size really matter? just ask evolution…

A while ago, I wrote a post about some of the evolutionary mysteries presented to us by women’s breasts, pointing out how sexual selection doesn’t completely explain their sizes and shapes. Today, we’ll take a look at another possible product of sexual selection, one that seems to be a little more clear cut. I’m talking about the penis of the human male, the biggest in length, girth, absolute size and in proportion to the body when put up against that of all other ape species. But how did it get that way? Well, if evolutionary psychologist Carole Jahme is right, then the blame rests with you ladies. Thanks to your preferences in mates, the human penis grew in size to become more flexible, loosing the small bone of its evolutionary relatives. There weren’t many advantages to this change in physiology other than pleasing the female eye, among other things, but that’s all that matters from an evolutionary standpoint since without a shot at reproduction, your line will go extinct…

Of course there’s a bit more to it than that. Sexual selection is the same reason why peacocks have giant fans for tails, making them a potential target for fast predators. While it would seem that males with an extravagant plumage are easier to find, chase, and catch would branch off into something less conspicuous and far more subtle to avoid predation, the peahens prefer a male who can keep his outrageous plumage safe from both predators and competitors. Same applies to male lions whose dark, thick manes attract more females, and a giant deer which went extinct at the end of the Ice Age, the Irish Elk, which had a pair of titanic antlers to attract potential mates and intimidate rivals. Human penises followed the same selective pressures, as we see with typically male contests in which penis size serves to establish the perception of fertility and sexual athleticism in a bid to attract women and intimidate other men. Likewise, since human sperm compete to fertilize eggs, a larger set of testicles and higher sperm production would help fertilize more eggs and produce more offspring who inherit the sexual characteristics that should give them at least as good of a shot at reproducing as their parents, assuming they’ll get to puberty; which at one time was no guarantee.

So what about the often heard male question regarding whether he’s adequately endowed to attract women’s attention? If sexual selection can explain why humans have the genitals they do today, could it provide at least a couple of clues there? Well, as a matter of fact, it can. While for many young men the idea of adequate size comes from adult entertainment, porn is really a bad source of information here because it portrays a narrow slice of the population based on very subjective criteria. Instead, we can look at the distribution of penis sizes as measured by condom maker Ansell, which shows that nearly 25% of males have a penis which measures between 5.5 and 6 inches. After the 6 inch mark, there’s a rapid drop-off in sizes and males endowed with 7 or more inches make up just 5% of the population compared to the 70% of males with a length between 5.5 and 7 inches. What does that tell us? If women preferred very large penises, we would expect to see either a more even distribution of male endowments between 5.5 and 9 inches (the largest size recorded by the survey, just under 0.1% of the group), or a skew towards the larger end of the scale. This indicates that the preferred size for human females is in the 5.5 to 7 inch range, primarily between 5.5. and 6.5 inches. Seven inches and over is more of an oddity, the likes of which we tend to see in porn.

On a side note though, it might be interesting to look back after a number of generations to note if penis sizes increased in any meaningful way thanks to the influence of pop culture. My guess would be that constraints on the male anatomy will stay in place for quite a while since there’s more to sex than just a certain penis size. A male at the top 1% of the size distribution chart might actually cause a lot more pain than pleasure. After all, in this case of sexual selection it’s about what women want, not necessarily what males think will intimidate the competition and make a statement to a potential mate, and the size distribution shows that quite well…