Sex ratio dynamics and fluctuating selection on personality

► Fluctuating selection can explain the maintenance of genetic variation in phenotypic traits. ► Sex ratios powerfully affect social behavior, thus driving selection on personality traits. ► Sex ratio dynamics are intrinsically unstable and fluctuating. ► In humans, sex ratio dynamics may contribute to maintain genetic variation in personality. ► The sex ratio hypothesis can be applied to both humans and nonhuman species.