In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency (F 0 ) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F 0 sexual dimorphism than any other ape. We also show that low-F 0 vocalizations predict perceptions of men's dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F 0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

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Fluctuating asymmetry (FA), deviation from perfect bilateral symmetry, is thought to reflect an organism's relative inability to maintain stable morphological development in the face of environmental and genetic stressors. Previous research has documented negative relationships between FA and attractiveness judgments in humans, but scant research has explored relationships between the human voice and this putative marker of genetic quality in either sex. Only one study (and in women only) has explored relationships between vocal attractiveness and asymmetry of the face, a feature-rich trait space central in prior work on human genetic quality and mate choice. We therefore examined this relationship in three studies comprising 231 men and 240 women from two Western samples as well as Hadza hunter-gatherers of Tanzania. Voice recordings were collected and rated for attractiveness, and FA was computed from two-dimensional facial images as well as, for a subset of men, three-dimensional facial scans. Through meta-analysis of our results and those of prior studies, we found a negative association between FA and vocal attractiveness that was highly robust and statistically significant whether we included effect sizes from previously published work, or only those from the present research, and regardless of the inclusion of any individual sample or method of assessing FA (e.g., facial or limb FA). Weighted mean correlations between FA and vocal attractiveness across studies were-.23 for men and-.29 for women. This research thus offers strong support for the hypothesis that voices provide cues to genetic quality in humans.

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Across human societies and many nonhuman animals, males have greater interest in uncommitted sex (more unrestricted sociosexuality) than do females. Testosterone shows positive associations with male-typical sociosexual behavior in nonhuman animals. Yet, it remains unclear whether the human sex difference in sociosexual psychology (attitudes and desires) is mediated by testosterone, whether any relationships between testosterone and sociosexuality differ between men and women, and what the nature of these possible relationships might be. In studies to resolve these questions, we examined relationships between salivary testosterone concentrations and sociosexual psychology and behavior in men and women. We measured testosterone in all men in our sample, but only in those women taking oral contraception (OC-using women) in order to reduce the influence of ovulatory cycle variation in ovarian hormone production. We found that OC-using women did not differ from normally-ovulating women in sociosexual psychology or behavior, but that circulating testosterone mediated the sex difference in human sociosexuality and predicted sociosexual psychology in men but not OC-using women. Moreover, when sociosexual psychology was controlled, men’s sociosexual behavior (number of sexual partners) was negatively related to testosterone, suggesting that testosterone drives sociosexual psychology in men and is inhibited when those desires are fulfilled. This more complex relationship between androgen and male sexuality may reconcile some conflicting prior reports.