Next, 29 heterosexual Latvian women looked at photographs of the men’s faces and bodies separately and judged them on attractiveness. All of the women were in the fertile phases of their menstrual cycles, as judged by counting back from the last menstrual period to the day of likely ovulation.

A separate group of 20 heterosexual Finnish men and women rated the men for masculinity, and 14 other Latvian women rated the men’s facial fatness, or adiposity, which is highly related to overall body fatness.

The results revealed that fatness, as measured with facial adiposity, was linked to both antibody response and attractiveness, with pudgier men both having weaker immune systems and being seen as less appealing by the fertile women. A statistical analysis found that contrary to what the immunocompetence handicap would suggest, masculinity was not linked to either immune response or bodily or facial attractiveness.

“We found that a man’s weight serves as a better indicator of the relationship between immune response and attractiveness than masculinity does,” Coetzee said. “It is therefore more likely that Latvian women use weight, rather than masculinity, in their subconscious judgments of a man’s immunity.”