Penis size may matter more to men than women

Human history is full of juvenile jokes, odd stereotypes, and outright harmful misinformation about the size of a man’s penis. But the long and short of the real science behind size suggests that men themselves are more likely than women to get riled up about the subject. According to a study published today in the journal PLOS Biology, men routinely feel more physically and sexually threatened by well-endowed rivals—regardless of how women feel about the subjects.

For years, evolutionary biologists have remained confused by one peculiar aspect of human anatomy. In relation to overall body size, the human penis is usually larger than those belonging to most other primates. The reasons why have remained unclear, although there are plenty of theories related to attracting mates, warding off opponents, and even improving reproductive success.

Three computer generated male figures of varying body and penis size — *Examples of the computer-generated, male figures used in the study. Credit: Aich U, et al., 2025, PLOS Biology, CC-BY 4.0*

To better understand the psychological influences on humanity’s sexual history, researchers at the University of Western Australia asked over 600 men and 200 women to review computer-generated male bodies with varying shapes, heights, and penis sizes. The men then assessed each example based on how physically and sexually intimidated they felt by them. Meanwhile, the women rated each figure’s hypothetical sexual attractiveness. Each participant either saw a life-sized image or a scaled-to-size alternative.

Women most often ranked male bodies more attractive when they exhibited a higher shoulder-to-hip ratio (i.e. a V-shape) and a larger penis. That said, these attributes had their limits. There came a point when overall body and penis sizes offered diminishing returns.

Men, if you can believe it, were often a bit more sensitive about possible rivals. Unlike the study’s other volunteers, men consistently rated their same-sex opponents more intimidating as both body and penis sizes increased—with no cap on measurements. At the same time, they also viewed men with larger attributes as a greater sexual threat. Compared with the women’s responses, it appears many men really do believe size matters more than it often does.

The team says that their work offers the first experimental evidence of its kind that men assess penis size to judge an opponent’s fighting and sexual prowess. The overlapping responses from both sexes also suggest that increased human penis size is an evolutionary adjustment to attract mates.

“While the human penis functions primarily to transfer sperm, our result suggests its unusually large size evolved as a sexual ornament to attract females rather than purely as a badge of status to scare males,” Michael Jennions, a study co-author and University of Western Australia evolutionary biologist, said in a statement. “Although it does both,” he added.