A perennial topic of locker room banter and sex columns has caught the attention of scientists: Do women find bigger penises more attractive? The answer, it turns out, is yes. But it’s not a purely bigger-is-better relationship. The attractiveness of a larger penis is intertwined with height and body shape, new research suggests.
Much research has been devoted to the male genitalia of insects, beasts, fish and fowl. But man has fallen by the wayside, says Brian Mautz, an evolutionary biologist at the University of Ottawa in Canada who led the new work. The handful of studies that have examined whether penis length in Homo sapiens affects attractiveness have looked at penis size alone, rather than size as part of a package of traits. And research that has relied on direct questioning of women has yielded mixed results: Depending on the study, women prefer longer penises or wider penises, or think penis size is unimportant.
“People tend to give socially desirable or politically correct answers,” says Mautz, who has studied mating behavior in fiddler crabs, fish, crickets and flies. Yet the upright body posture of humans, along with a protruding, nonretractable penis that stands out from the hair surrounding it, suggests to many biologists that the organ’s conspicuousness is no accident. Perhaps female choice has even driven an increase in human penis size over evolutionary time, Mautz says. Because humans have probably covered their genitals with clothing for most of their history, however, it isn’t clear what opportunities females would have had to exert their preference.
Mautz and Australian colleagues generated computer images of a male figure and toggled three traits: flaccid penis length, height, and shoulder-to-hip ratio (creating torsos on the spectrum from V-shaped to heavily love-handled). The researchers recruited 105 Australian women and had each rate the attractiveness of 53 figures, a subset of the 343 generated by creating seven different penis lengths, seven heights and seven shoulder-to-hip ratios.
The figures with larger penises were rated considerably more attractive, the researchers report April 8 in the Proceedings of the National Academies of Sciences. Teasing apart the effects of the various traits suggests that penis length influences attractiveness about as much as height, a trait with a well-documented influence on male reproductive success.
“This was quite surprising,” Mautz says. “Height is one of the most studied traits — it influences how much money a man makes, his place on the leadership scale and how many children he has. To find that penis size has the same effect is quite surprising.”
The researchers found no maximum preferred penis size — the male figures generated for the study topped out at 13 centimeters, about 5 inches. Yet penis size alone doesn’t override the relative unattractiveness of being wide-of-hip and short-of-stature. A larger penis did little to increase the attractiveness of the shorter, pear-shaped male figures.
The study “is really great,” says behavioral ecologist Patricia Brennan of the University of Massachusetts Amherst, whose recent research has focused on duck penis length and shape. Sexual signals in nature are often complex affairs — sage grouse for example, have a whole presex mating display that combines physical traits, such as an inflated air sac and contrasting plumage, with vocalizations and strutting. “Female choice in most species is quite complicated,” Brennan says. “But sometimes we find that males are doing 10 things and females are paying attention to only one.”
The study can’t answer whether the attractiveness of longer organs to females has influenced penis length over human evolution. In some ducks, for example, average penis size grows when more males are around.
“Genitalia really are hugely important evolutionarily,” Brennan says. “It’s a crucial place to look if we want to understand why some organisms are more successful than others.”
It’s important to differentiate between finding a trait attractive and choosing it in a mate, says evolutionary biologist William Eberhard of the Smithsonian Tropical Research Institute and the Universidad de Costa Rica. If flaccid penis length truly affects female choice in a mate — which the study didn’t establish — that would be very unusual, Eberhard says. As genitalia go, female choice is typically influenced by traits relating to the mating act itself, not presex genital displays. “This is a small piece of what may be a very interesting story,” he says.
Researchers ought to look at the research question across cultures, says Alan Dixson, an expert in primate sexuality at Victoria University of Wellington in New Zealand, who has studied the male penis’s attractiveness to women in several cultures. While women in the new study do seem to rate a bigger penis as better, the increase in attractiveness seems modest but might not be universal, he says.