A new study from the University of Western Australia explored whether penis size affects female attraction and male perception of rivalry. The research involved over 800 participants—more than 600 men and 200 women—who evaluated anatomically accurate, computer-generated male figures varying in height, shoulder-to-hip ratio, and flaccid penis length. Women rated sexual attractiveness, while men assessed physical threat and sexual competitiveness. Some participants viewed life-sized projections in a lab, while others used scaled images online.

The findings, published in PLOS Biology, showed that women generally preferred taller men with broader shoulders and a V-shaped body. Penis size increased attractiveness only up to about four inches flaccid; beyond that, interest decreased. Men, in contrast, continued to see larger sizes as more threatening.

Dr. Upama Aich explained, “Females rated taller figures with a higher shoulder-to-hip ratio and a larger penis as more attractive. However, beyond a certain point, further increases had diminishing benefits.”

She added, “Males also rated taller, V-shaped, and larger-penis figures as more intimidating sexual rivals. Unlike females, men consistently ranked exaggerated traits as more of a threat, suggesting they overestimate their importance for attracting females.”

Height and body shape were more influential than penis size in how men judged rivals, though penis length still affected perceptions of competition. Individual traits also mattered: taller women emphasized male height, and older men gave greater weight to penis size.

Reflecting on evolution, Dr. Aich noted that, relative to body size, the human penis is larger than other primates. Before clothing, it would have been a prominent feature affecting mate choice and competition.

Co-author Professor Michael Jennions said, “While the human penis functions primarily to transfer sperm, our results suggest its large size evolved as a sexual ornament to attract females rather than purely as a badge of status, though it influences both.”

Overall, the study provides experimental evidence that penis size influences both mate selection and male rivalry, while highlighting a mismatch: men overemphasize traits that women value only moderately.