Covariation of life history traits across species may be organised on a 'fast-slow' continuum.A burgeoning literature in psychology and social science argues that trait covariation should be similarly organised across individuals within human populations. Here we describe why extrapolating from inter-species to inter-individual trait covariation is not generally appropriate. The process that genetically tailors species to their environments (i.e. Darwinian evolution) is fundamentally different from processes that tailor individuals to their environments (e.g. developmental plasticity), so their outcomes in terms of trait covariation need not be parallel or even related. We discuss why correlational selection, physical linkage, pleiotropy, and non-random mating do not substantively affect this claim in the context of complex human traits. We also discuss life history trade-offs and their relation to interindividual trait covariation. We conclude that researchers should avoid hypotheses and explanations that assume trait covariation will correspond across and within species, unless they can mount a theoretically coherent argument to support this claim in the context of their research question.

Women’s preferences for men’s androgen dependent secondary sexual traits are proposed to be phenotypically plastic in response to exposure to pathogens and pathogen disgust. While previous studies report that masculinity in facial shape is more attractive to women who have recently been exposed to pathogenic cues and who are high in self-reported pathogen disgust, facial hair may reduce male attractiveness under conditions of high pathogens as beards are a possible breeding ground for disease carrying ectoparasites. In the present study, we test whether women’s preferences for beardedness and facial masculinity vary due to exposure to different pathogenic cues. Participants (N = 688, mean age + 1SD = 31.94 years, SD = 6.69, range = 18–67) rated the attractiveness of facial composite stimuli of men when they were clean-shaven or fully bearded. These stimuli were also manipulated in order to vary sexual dimorphism by ±50%. Ratings were conducted before and after exposure to one of four experimental treatments in which participants were primed to either high pathogens (e.g. infected cuts), ectoparasites (e.g. body lice), a mixture of pathogens and ectoparasites, or a control condition (e.g. innocuous liquids). Participants then completed the three-domain disgust scale measuring attitudes to moral, sexual and pathogen disgust. We predicted that women would prefer facial masculinity following exposure to pathogenic cues, but would show reduced preferences for facial hair following exposure to ectoparasites. Women preferred full beards over clean-shaven faces and masculinised over feminised faces. However, none of the experimental treatments influenced the direction of preferences for facial masculinity or beardedness. We also found no association between women’s self-reported pathogen disgust and their preferences for facial masculinity. However, there was a weak positive association between moral disgust scores and preferences for facial masculinity, which might reflect conservatism and preferences for gender typicality in faces. Women’s preferences for beards were positively associated with their pathogen disgust, which runs contrary to our predictions and may reflect preferences for high quality individuals who can withstand any costs of beardedness, although further replications are necessary before firm conclusions can be made. We conclude that there is little support for pathogenic exposure being a mechanism that underpins women’s directional preferences for masculine traits.

Sex differences in misperceptions of sexual interest have been well documented; however, it is unclear whether this cognitive bias could be explained by other factors. In the current study, 1,226 participants (586 men, 640 women) participated in a speed-dating task in which they rated their sexual interest in each other as well as the sexual interest they perceived from their partners. Consistent with previous findings, results showed that men tended to overperceive sexual interest from their partners, whereas women tended to underperceive sexual interest. However, this sex difference became negligible when we considered potential mediators, such as the raters’ sociosexual orientation and raters’ tendency to project their own levels of sexual interest onto their partners. These findings challenge the popular notion that sex differences in misperceptions of sexual interest have evolved as a specialized adaptation to different selection pressures in men and women.

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According to the dual mating strategy model, in short-term mating contexts women should forego paternal investment qualities in favor of mates with well-developed secondary sexual characteristics and dominant behavioral displays. We tested whether this model explains variation in women's preferences for facial masculinity and beardedness in male faces. Computer-generated composites that had been morphed to appear +/-50% masculine were rated by 671 heterosexual women (M age = 31.72 years, SD = 6.43) for attractiveness when considering them as a short-term partner, long-term partner, a co-parent or a friend. They then completed the Revised Sociosexual Inventory (SOI-R) to determine their sexual openness on dimensions of desire, behavior, and attitudes. Results showed that women's preferences were strongest for average facial masculinity, followed by masculinized faces, with feminized faces being least attractive. In contrast to past research, facial masculinity preferences were stronger when judging for co-parenting partners than for short-term mates. Facial masculinity preferences were also positively associated with behavioral SOI, negatively with desire, and were unrelated to global or attitudinal SOI. Women gave higher ratings for full beards than clean-shaven faces. Preferences for beards were higher for coparenting and long-term relationships than short-term relationships, although these differences were not statistically significant. Preferences for facial hair were positively associated with global and attitudinal SOI, but were unrelated to behavioral SOI and desire. Although further replication is necessary, our findings indicate that sexual openness is associated with women's preferences for men's facial hair and suggest variation in the association between sociosexuality and women's facial masculinity preferences.

Covariation of life history traits across species may be organised on a ‘fast-slow’ continuum. A burgeoning literature in psychology and social science argues that trait covariation should be similarly organised across individuals within human populations. Here we describe why extrapolating from inter-species to inter-individual trait covariation is not generally appropriate. The process that genetically tailors species to their environments (i.e. Darwinian evolution) is fundamentally different from processes that tailor individuals to their environments (e.g. developmental plasticity), so their outcomes in terms of trait covariation need not be parallel or even related. We discuss why correlational selection, physical linkage, pleiotropy, and non-random mating do not substantively affect this claim in the context of complex human traits. We also discuss life history trade-offs and their relation to inter-individual trait covariation. We conclude that researchers should avoid hypotheses and explanations that assume trait covariation will correspond across and within species, unless they can mount a theoretically coherent argument to support this claim in the context of their research question.

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Objectives: Intra-sexual selection has shaped the evolution of sexually dimorphic traits in males of many nonhuman primates, including humans. In men, sexual dimorphism in craniofacial shape (i.e. facial masculinity) and facial hair have both been shown to communicate aspects of social and physical dominance intra-sexually. However, less attention has been given to how variation in physical and social dominance among receivers impacts on perceptions of facial masculinity and beards as intra-sexual signals of formidability.Methods: In the current study, male participants (N = 951) rated male faces varying in masculinity and beardedness when judging masculinity, dominance and aggressiveness.These participants also responded to scales measuring their psychological dominance, sexual jealousy, status seeking and masculine morphology (facial masculinity, facial hair, and height).Results: Beardedness exerted strong effects over clean-shaven faces on ratings of masculinity, dominance and aggressiveness. Trait ratings of masculinity, dominance, and aggressiveness rose linearly with increasing craniofacial masculinity. The significant facial masculinity × facial hair interaction suggests that beardedness caused strong effects on all trait ratings over clean-shaven faces at every level of facial masculinity. Participants with full beards also reported higher scores on dominance and assertiveness scales. Participants high in dominance and assertiveness also gave higher ratings for dominance, but not masculinity or aggressiveness, to bearded over clean-shaven faces. Participants low in intra-sexual jealousy rated clean-shaven and/or feminised faces as less dominant, less masculine, and less aggressive.Conclusions: These findings demonstrate that facial hair enhances perceptions of masculinity, dominance and aggressiveness above ratings of facial masculinity, potentially by augmenting masculine craniofacial features. Individual differences in intra-sexual dominance showed associations with judgments of facial hair but not facial masculinity. Our study demonstrates that when two sexually dimorphic androgen dependent facial traits are judged in concert, ornamental rather than structural masculine facial features underpin men's intrasexual judgments of formidability.