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 local population 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 sex ratio of the local population and assessing women’s preferences for facial symmetry, a putative cue of mate quality in humans. In both experiments, viewing slideshows with varied sex ratios 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 local population increased the salience of facial cues of quality in that sex, which may support adaptive appraisals of both potential mates’ and competitors’ quality. This effect of sex ratio 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 local population, whereby the degree of variation in men’s, but not women’s, attractiveness modulated symmetry preferences. These findings demonstrate that symmetry preferences in humans are influenced by cues to the sex ratio of the local population in ways that complement both the facultative responses that have been observed in many other species and theories of both intersexual and intrasexual selection.

► The ratio of males to females influences behaviour in many nonhuman species.
► Here we show cues to the ratio of men to women influence attractiveness judgements.
► Women preferred symmetric men more after exposure to cues that men were plentiful.
► This effect was independent of the effects of variation in attractiveness.
► Shows women recalibrate attractiveness judgements according to sex ratio cues.