Humans can accurately extract information about men's formidability from their faces; however, the actual facial cues that inform these judgments have not been established. Here, through three studies, we test the hypothesis that bizygomatic width (i.e. facial width-to-height ratio, fWHR) covaries with actual physical formidability (hypothesis #1) and that humans use this cue when making assessments of formidability (hypothesis #2). Our data confirm that fWHR is predictive of actual fighting ability among professional combatants (study 1). We further show that subjects' assessments of formidability covary with the target's fWHR on natural faces (study 2), computer-generated images of strong and weak faces (study 2), and experimentally manipulated computer-generated faces (study 3). These results support the hypothesis that bizygomatic width is a cue of formidability that is assessed during agonistic encounters.

Several lines of evidence suggest that facial-width-to-height ratio (fWHR) provides an accurate cue to men's formidability, thus providing observers with a reliable estimate of their potential success in an interpersonal physical conflict. The degree to which fWHR provides the same information in women's faces, however, remains unclear. In fact, morphological characteristics, such as body size, may be more effective indicators of formidability in women. In the present study, we analyzed the effects of both fWHR and body mass index (BMI) on total number of fights and total number of wins in female competitive Ultimate Fighting Challenge (UFC) fighters. After controlling for number of active years fighting, we found that BMI significantly predicted number of wins in female fighters. The effects of fWHR were not significant, but warrant replication with a larger sample. These results suggest that in women, body size, rather than fWHR, may be a more accurate indicator of success in aggressive interpersonal conflicts. Our findings contribute to a growing body of literature that shows distinct differences in men and women's interpersonal aggressive and dominance behavior, as well as their morphological indicators.

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