The popular claim that women in their fertile days prefer men with more masculine faces may not be true. That’s the conclusion of the largest study to analyze how sex hormones influence women’s preference for men’s faces. Researchers first created 10 prototype male faces by averaging 50 photos of young white men. Then, they tweaked the prototype faces to create a more masculine and a more feminine version of each (pictured, masculine version on the left, feminine version on the right). Finally, the scientists asked nearly 600 heterosexual women to look at these photos and rate men’s attractiveness for either a fling or a long-term relationship. The women also provided saliva samples, which the researchers tested for sex hormones such as estradiol and testosterone. Hormone levels were not significantly related to women’s preference for manly faces, the team reports on the preprint server bioRxiv. The researchers also didn’t find evidence that women using the birth control pill prefer more feminine faces, as had been suggested. However, women did prefer masculine faces over feminine ones, especially for short-term relationships. This could be because manly traits, like a large jaw and jutting cheekbones, signal good heritable characteristics, such as a strong immune system, but have also been linked to people that are less willing to invest time in personal relationships, the scientists say.