A new study published in the Journal of Evolutionary Biology has found an association between facial masculinity and men’s semen quality — but the results are contrary to what one might expect.

The study found that men with more masculine facial features tended to have poorer semen quality.

In the study, 64 women and 24 men rated the facial attractiveness of another 50 men who were between the ages of 18 and 36. The researchers also analyzed 13 metric parameters of the 50 men’s faces to determine their level of facial masculinity, and tested the 50 men’s semen quality.

The researchers wrote that “male semen quality was negatively associated with the male cheekbone (facial) width and thus masculinity. Facial width has been demonstrated to be positively associated with the testosterone levels in men and also predicted number of testosterone- linked behavioural traits, such as aggressiveness, dominance, physical strength, status, financial success and deceptiveness.”

They explained that increased levels of testosterone have been demonstrated to impair sperm production, and this finding may indicate a trade-off between investments in secondary sexual signaling (i.e. facial masculinity) and fertility.

“Sperm competition theory predicts that males face a trade-off between investments in attracting females and gaining fertilizations. Thus, males that invest significant amount of their resources on attracting mates or male–male competition may have fewer resources available to produce high-quality semen. Existence of such trade-off has demonstrated in several empirical studies both in various animal species.”

Interestingly, males estimated facial images generally more attractive than females did, suggesting that males may generally overestimate the attractiveness of other men to females.