Cues to the sex ratio of the local population influence women's preferences for facial symmetry

In nonhuman species, increasing the proportion of potential mates in the localpopulation often increases preferences for high-quality mates, while increasing the proportion of potential competitors for mates intensifies within-sex competition. In two experiments, we tested for analogous effects in humans by manipulating pictorial cues to the sexratio of the localpopulation and assessing women’spreferences for facialsymmetry, a putative cue of mate quality in humans. In both experiments, viewing slideshows with varied sexratios tended to increase preferences for symmetry in the sex that was depicted as being in the majority and tended to decrease preferences for symmetry in the sex that was depicted as being in the minority. In other words, increasing the apparent proportion of a given sex in the localpopulation increased the salience of facialcues of quality in that sex, which may support adaptive appraisals of both potential mates’ and competitors’ quality. This effect of sexratio was independent of (i.e. did not interact with) an effect of cues to the degree of variation in the attractiveness of individuals in the localpopulation, whereby the degree of variation in men’s, but not women’s, attractiveness modulated symmetrypreferences. These findings demonstrate that symmetrypreferences in humans are influenced by cues to the sexratio of the localpopulation in ways that complement both the facultative responses that have been observed in many other species and theories of both intersexual and intrasexual selection.