However, past studies have often revealed that men with high testosterone levels are not automatically appealing to women, who view such testosterone-laden men as having long-term drawbacks. For instance, the macho guys may lead a “player’s” lifestyle, or may also be bad parents.

Instead, human behavioral ecologist Fhionna Moore at the University of Abertay Dundee in Scotland and her colleagues focused on the stress-linked hormone cortisol. Persistently high levels of cortisol can suppress not just the immune system, but also reproductive function. As such, it would make sense if women preferred men with low cortisol levels — that is, those who are not stressed out.