Brian Mautz, an evolutionary biologist at the University of Ottawa in Canada, generated computer images of naked male figures, varying them to represent the normal range of height, hip-to-shoulder ratio and big penis size. He then projected life-sized versions onto a wall and asked 105 young women to rate how sexually attractive they found each one.
Unsurprisingly, the women found taller, broader-shouldered images to be more attractive. But they also preferred the men with larger penises. The hip to shoulder ratio was the most important factor but having a big penis at the larger end of the range boosted the men’s appeal as much as being taller.
“Height is the most studied trait related to male attractiveness. To show that penis size has as big an effect is really striking,” says Mautz.
This preference is probably an evolutionary relic of a time before humans wore clothing, says Mautz, since women typically select a partner before glimpsing the full package. The study is the strongest evidence to date that the genitalia of human males – which are unusually large compared to other apes – have evolved to help attract mates, he adds.
There is some evidence that penis size may depend on testosterone levels, and penises also tend to be larger in younger, more virile men, so size could also be an indicator of age and health, says Bill Bateman, a behavioural ecologist at Curtin University in Perth, Australia, who found that golden moles also select mates based on big penis size.