When it comes to attracting a mate, it turns out that size does matter after all, according to a new study.
Research in the scientific journal PLOS Biology found that women tend to rate men with larger penises as more sexually attractive, while men view better-endowed rivals as more threatening—both physically and sexually.
The study was undertaken by evolutionary biologist Upama Aich of the University of Western Australia and her international team of colleagus who examined how physical traits shape perceptions in both mate choice and male–male competition.
While previous research has linked penis size to reproductive success—such as an increased likelihood of pregnancy—the evolutionary reasons for humans’ relatively unusually large phalluses have remained unclear.
Before clothes were invented, the penis would have been a visible feature, potentially signaling information to both potential mates and rivals, the researchers explained.
Scientists have proposed that a larger penis may have served to indicate higher testosterone levels, better health or greater fighting ability—all traits that could increase attractiveness to females or deter competition from other males.
To test these ideas, researchers recruited more than 600 men and over 200 women and asked them to rate computer-generated male figures that varied systematically in height, body shape and penis size.
Some participants viewed life-sized images in person, while others completed an online survey using scaled images. Each figure was presented as a video in which the figure rotated 30 degrees to the left and then 30 degrees to the right over four seconds.
The women participants were asked to assess sexual attractiveness. The results showed that women consistently rated figures that were taller; had a higher shoulder-to-hip ratio, reflecting a more V-shaped torso; and a larger penis as more attractive.
Beyond certain thresholds, increases in height, penis size and shoulder breadth produced diminishing returns in attractiveness.
Male participants, meanwhile, were asked to judge how intimidating the computer-generated figures appeared, both as potential fighting opponents and as sexual rivals.
The men ranked taller, more muscular figures with larger penises as more threatening on both counts. Unlike the women participants, men tended to view increasingly exaggerated traits as steadily increasing a rival’s sexual threat, suggesting that men may overestimate how much these features matter to women.
“Males were more likely to feel threatened if they had to imagine being challenged by a rival with a large penis,” the authors explained.
“We infer that this translates into males being less likely to initiate an aggressive interaction with a rival with a large penis.”
However, the researchers noted that penis size appeared to play a stronger role in sexual attractiveness than in assessments of fighting ability. Height and body shape had a greater influence on how men judged other men as potential threats.
Co-author Michael D. Jennions said the results point to the penis functioning as more than a reproductive organ.
“While the human penis functions primarily to transfer sperm, our result suggests its unusual large size evolved as a sexual ornament to attract females rather than purely as a badge of status to scare males, although it does both,” he said.
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Reference
Aich, U., Tan, C., Bathgate, R., Blake, K. R., Capp, R. C. S., Kuek, J. C., Wong, B. B. M., Mautz, B. S., & Jennions, M. D. (2026). Experimental evidence that penis size, height, and body shape influence assessment of male sexual attractiveness and fighting ability in humans. PLOS Biology, 24(1). https://doi.org/10.1371/journal.pbio.3003595
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