Alexander K. Hill

Sexual selection on male vocal fundamental frequency in humans and other anthropoids

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 (F0) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F0 sexual dimorphism than any other ape. We also show that low-F0 vocalizations predict perceptions of mens dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

Fulfilling desire: Evidence for negative feedback between men's testosterone, sociosexual psychology, and sexual partner number

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, mens 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 androgens and male sexuality may reconcile some conflicting prior reports.

How Well Do Men's Faces and Voices Index Mate Quality and Dominance?

Previous studies have used self-ratings or strangers’ ratings to assess men’s attractiveness and dominance, attributes that have likely affected men’s access to mates throughout human evolution. However, attractiveness and dominance include more than isolated impressions; they incorporate knowledge gained through social interaction. We tested whether dominance and attractiveness assessed by acquaintances can be predicted from (1) strangers’ ratings made from facial photographs and vocal clips and (2) self-ratings. Two university social fraternities, their socially affiliated sororities, and independent raters evaluated men’s short- and long-term attractiveness, fighting ability, and leadership ability. Ratings made by unfamiliar men using faces, but not voices, predicted acquaintance-rated fighting and leadership ability, whereas ratings made by unfamiliar women from faces and voices predicted acquaintance-rated short- and long-term attractiveness. Except for leadership, self-ratings aligned with peers’ evaluations. These findings support the conclusion that faces and voices provide valuable information about dominance and mate quality.

Sexual Selection on Human Voices

Vocal communication is important in many mammals, including many nonhuman primates, but in no species is it more important than in humans. Given the relevance of vocal communication to both men and women, it is conspicuous that some of the largest human sex differences occur in the voice. Understanding why men’s and women’s voices differ as dramatically as they do promises to elucidate human communication and social dynamics in general and human mating and status competition in particular. We review research suggesting that sexual selection shaped the acoustic features of the human voice and consider how mate choice and contest competition may have influenced women’s and men’s voices. We find that male mate choice may have maintained high, youthful-sounding voices in women, perhaps because feminine voices advertise women’s fertility. We also review evidence that men’s voices were shaped by female mate choice and male contests and advertise men’s mate value and threat potential and that women’s preferences for and men’s deference to masculine voices reflect this information content. We discuss data suggesting that vocal masculinity influences men’s mating opportunities and reproduction and conclude by highlighting directions for future research.

Gorillas in Our Midst? Human Sexual Dimorphism and Contest Competition in Men

Abstract The literature on human sexual selection has historically focused on the role of female mate choice, but cumulating experimental, correlational, and cross-cultural evidence suggests that male contest competition may have been more influential in shaping mens phenotypes. Cross-species comparison has shown similarities between humans and our closest extant phylogenetic relatives, the Great Apes, in male–male aggression, and archeological evidence also indicates a great antiquity for male–male violence. Compared to women, men possess substantially greater muscle mass, strength, cranial robusticity, physical aggression, pain tolerance, risk-taking, weapons use, and participation in coalitional aggression. Men also exhibit displays of physical prowess and acuity to the formidability of male conspecifics, as well as possessing a suite of traits, such as facial hair and low vocal pitch, that increase perceptions of dominance. These traits are consistent with having been shaped by contest competition over mates: they are sexually dimorphic, appear at sexual maturity, and predict success in male contests as well as success in mating and reproduction. While alternative explanations for some of these sexually dimorphic traits are possible, contest competition among males throughout human evolutionary history is the most parsimonious.

The long and the short of it: new insights on sperm length help demystify the complexities of sexual selection.

Human sperm are approximately 6000th of a centimeter long, a small fraction of a mans total body length. By contrast, fruit fly (Drosophila spp.) sperm can reach nearly 6 cm, roughly twenty times the total length of their bodies. This dramatic variation in male reproductive biology is explored in a recent paper from the journal Nature.1 While the literature on sperm competition has for decades emphasized the fitness benefit males of many species accrue by producing small gametes in large quantities, understanding species whose males produce large gametes in small quantities while remaining competitive for fertilizations has until recently proven more difficult. Stefan Lüpold and colleagues suggest a solution to this “big-sperm paradox.”