Compared to other primates, humans have a larger penis relative to body size, which has long fascinated researchers. Now, a group of scientists at the University of Western Australia have attempted to get to the bottom of how a large human penis affects other men and women.
Previous studies have presented explanations for the relatively large size, such as that the size may affect a woman's chance of getting pregnant, but also that women would find a man with a large penis more attractive. A third explanation is that it deters rival men.
Threatening rivals
The researchers had 600 men and 200 women look at computer-generated images of men of different heights, body shapes and penis sizes. The women were asked to rate how sexually attractive the men in the images were, while the men were asked to rate how physically threatening they perceived the images to be and to what extent they were perceived as sexual rivals.
The findings show that women generally perceive tall men with a V-shaped body (broad shoulders) and larger penises as more attractive than short men with a more pear-shaped body and small penises. However, there seems to be a limit, around 12 centimeters in the flaccid state, after which women no longer perceive additional length as more sexually attractive.
Men see rivals
For the men watching, it was different. Unlike the women, the men consistently rated men with more V-shaped bodies and longer genitals as more threatening, both physically and as sexual rivals. This suggests, according to the researchers, that men tend to overestimate the importance of penis size in attracting women.
"Although the human penis primarily functions to transfer sperm, our results suggest that its large size evolved as a sexual ornament to attract women, rather than simply as a status symbol to intimidate men," said Michael Jennions, one of the study authors, in a press release.
