A new study suggests manhood size subtly shapes how men judge potential competition – both in the gym and the dating arena
When men size each other up, it turns out the assessment may go deeper than height, shoulders, or muscle. New research suggests another physical trait quietly factors into how men judge potential rivals: the size of their genitals.
A study led by Upama Aich at the University of Western Australia, published in PLOS Biology, found that men perceive rivals with larger appendages as more threatening – both physically and sexually.
The research taps into a long-standing puzzle in evolutionary biology. Compared with other primates, humans have an unusually large package relative to body size. Scientists have long debated why. One theory is simple: before clothing existed, the penis was a visible trait that may have influenced both mate choice and male–male competition.
To investigate, researchers recruited more than 800 participants – over 600 men and 200 women. Volunteers evaluated computer-generated male figures that varied in height, body shape, and penis size. Women rated sexual attractiveness, while men judged how intimidating each figure seemed as both a potential fighter and a sexual rival.
The results were revealing.
Women consistently rated men with greater height, broader shoulders, and larger members as more attractive. But there was a limit: beyond a certain point, increasing those traits delivered diminishing returns.
Men’s responses told a slightly different story.
Male participants also found taller, V-shaped physiques and larger appendages more intimidating. But unlike women, they tended to see more exaggerated traits as increasingly threatening, suggesting men may overestimate how important these features are to women.
In other words: men think the competition is bigger than it actually is.
“Men rated rivals with larger penises as more physically threatening and sexually competitive,” said Aich.
Interestingly, manhood size wasn’t the strongest factor shaping men’s judgements. Height and upper-body shape had a bigger impact on how intimidating a rival appeared.
That aligns with what you might expect in the real world. Broad shoulders and height signal strength and fighting ability – traits that would have mattered in physical confrontations throughout human history.
Still, the findings suggest member size may have evolved as more than just reproductive anatomy.
Co-author Michael D. Jennions explains that while the penis primarily functions to transfer sperm, its unusually large size in humans may have developed partly as a sexual ornament—a trait that helps attract mates.
“It likely evolved to attract females rather than purely as a badge of status to scare males,” Jennions said. “Although it does both.”
For modern men, the takeaway is simpler.
When it comes to how other men perceive you, the big visual cues still dominate: height, posture, and a strong V-shaped build. The classic fitness markers remain the most powerful signals of strength and confidence.
Which means if you want to look more formidable – whether in the gym, on the street, or on a first date – the best investment is still the obvious one. Train your shoulders. Build your back. Stand tall.
