Sexual selection has shaped the evolution of male secondary sexual characteristics that communicate viability in many species1, including humans2. However, female preferences for males bearing attractive traits rarely converge on an optimal phenotype. This variation in preferences for sexually selected traits may occur in response to prevailing ecological, demographic and economic conditions3. Comparative studies suggest that men have a similar degree of sexually dimorphic secondary sexual trait development as nonhuman primate species with polygynous mating systems4, large social group sizes and complex multi-level social organizations5. This suggests that sexual selection via female choice and male-male competition has shaped the evolution of masculine traits in men2.

Men’s secondary sexual traits first appear during adolescence due to androgen exposure and are fully developed by young adulthood2. Physical masculinity may provide relevant information to potential mates and same-sex rivals regarding male reproductive maturity, underlying health, formidability, and social status2. One of the best studied sexually dimorphic traits is facial masculinity, which includes jaw size, brow ridge prominence, and robustness of the midface6. Facial masculinity is positively associated with some aspects of men’s health7,8 and disease resistance9. However, some research has not found this association10 or reported that a combination of facial masculinity and facial muscularity determines men’s immune response and women’s perceptions of men’s facial attractiveness11. Alternatively, facial masculinity may communicate more direct benefits like resource provisioning ability and protection2,12. More masculine looking men tend to have more muscular physiques13,14 and hence greater physical strength12, health15 and competitive ability16. Facial masculinity is also associated with behavioral dominance17, an open sociosexual orientation18, and higher social rank in same-sex dominance hierarchies19. Taken together, there is some evidence that women’s preferences for facial masculinity reflect selection for indirect (i.e. genetic) and direct benefits.

While several studies have reported masculine men to have higher mating success than less masculine men19,20, in many cases women’s preferences for facial masculinity are equivocal21 or less masculine-looking men are judged as more attractive than more masculine-looking men22,23,24. Variation in women’s preferences may be explained by the costs associated between masculinity and social traits25,26, as masculine looking men are perceived to be less warm, kind, and less paternally investing24,27. Further, masculine men state higher preferences for short-term than long-term relationships18,28, engage in more short-term relationships than their less masculine peers28 and women accurately assigned the likelihood of sexual infidelity from masculine facial shape in static photographs29. Thus, variation in preferences for masculine men may reflect choices for more prosocial partners and nurturing fathers over possible indirect and direct benefits associated with masculine facial traits30,31.

Evolutionary mating strategies theories propose that women overlook the costs of selecting less paternally investing masculine mates to secure benefits associated with phenotypic masculinity that could enhance offspring fitness32. Indeed, preferences for facial masculinity were highest among women living in countries and states within the U.S.A with lower national health33,34 and higher levels of pathogens35. These findings are bolstered by experimental studies reporting that exposure to cues of pathogens result in higher preferences for facial masculinity (36, but see 37). This suggests that any social costs of selecting masculine partners may be circumvented under conditions where potential indirect benefits may be realised. However, reanalysis of the data from DeBruine et al.33 reported that women’s preferences for facial masculinity were strongest in countries with high homicide rates and income inequality (indices of male intra-sexual competition) rather than reduced national health38,39. Experimental studies also demonstrate that women state higher preferences for facial masculinity following exposure to cues of male-male violence40. It is therefore possible that women’s preferences for masculine mates are stronger under conditions favoring direct material contributions rather than indirect genetic benefits.

Variation in women’s masculinity preferences could also emerge as a consequence of the density of available mates within the mating pool, whereby the saliency of masculine ornaments as attractive signals is stronger in larger and more complex social systems40,41. Recent research has found support for this hypothesis, as women’s preferences for masculine facial traits are stronger in larger cities with greater income disparity40 and in cultures with high human developmental indices41. This could indicate that under conditions where individuals assess the value of potential mates and rivals from among many anonymous conspecifics, masculine facial features become important as cues of distinctiveness41. Experimental evidence also shows causative effects of frequency dependence on women’s mate preferences, whereby masculine traits are more attractive when they are rare than when they are common42. However, whether women’s mate preferences for masculine characters are stronger when indirect or direct benefits may be prioritized, or whether economic development best explains variation, remains to be determined.

In addition to demographic variables, individual differences in mating strategies may contribute to the maintenance of variation in women’s preferences for facially masculine mates. Thus, women’s preferences for masculine traits may become stronger under conditions where the costs of lower paternal investment are reduced32. Indeed, women’s preferences for masculine faces, bodies, voices and odors are stronger when considering short-term than long-term mates43. Preferences for masculine partners as short-term mates may be strongest at the peri-ovulatory phase of the menstrual cycle, when any indirect benefits to offspring health and survivability could be acquired32. Initial research reported that women’s preferences for masculine physical, vocal, olfactory and behavioral traits were strongest at the peri-ovulatory phase of the menstrual cycle44. However, the majority of these studies employed indirect counting methods from questionnaires to ascertain women’s current fertility, which have been shown to be highly inaccurate compared measuring hormones45. Further, between-subject designs with small sample sizes were also methodological concerns in early studies of menstrual cycle effects on women’s mate preferences46. While some studies that measured women’s hormones to characterize current fertility reported women’s preferences for masculine characters were stronger when conception is more likely47, several recent studies have found no change in mate preferences among women at the peri-ovulatory phase for muscularity48,49, facial masculinity23,49,50, beards23,51, vocal masculinity52,53 and facial symmetry49. Thus, the extent to which ovulatory cycle shifts are associated with women’s mate preferences may have been overestimated in past research due to imprecise methodologies and small sample sizes54.

Individual differences in sociosexuality (SOI) are also associated with variation in women’s mate preferences. SOI refers to the desires, propensity to engage in and attitudes towards short-term, uncommitted and long-term, committed sexual partners55. More sexually open or unrestricted people report high scores for sexual openness, more sexual partners and may not place high importance on sexual monogamy. By contrast, people with a more restricted sociosexuality have fewer sexual partners and place greater importance on monogamy, love and fidelity55,56. SOI varies both within and between cultures in ways that conform to mating strategies theories. For example, willingness to participate in uncommitted sexual relationships is lower among people living under prevailing conditions of high parasite loads57,58 and where adult and infant survivability is low59. These patterns in sexual openness may reflect disease avoidance57 or direct benefits associated with bi-parental care under conditions where infant survival may be highly compromised59. As women’s preferences for facial masculinity may also reflect trade-offs between genetic quality and paternal investment33, individual differences and cross-cultural variation in SOI may predict women’s preferences for facial masculinity. While sociosexually open women state higher preferences for facial masculinity60,61,62, whether or not variation in women’s SOI and explains preferences for facial masculinity cross-culturally remains to be more fully explored33.

An important limitation in drawing conclusions across previous cross-cultural studies of women’s facial masculinity preferences concerns the statistical approaches employed63. Some cross-cultural research used aggregation at the national level to make claims relating to individual differences in mate choice33,38, which may inflate individual-level differences in preferences63. Further, cross-national demographic variables concerning health, violence, and economic stability are highly inter-correlated, such that unique variance attributable to specific demographic variables is challenging to expose when using aggregate national-level data63. The current study addresses these issues using facial masculinity preferences collected among 4483 heterosexual women from 34 countries. We employed mixed effects modelling to quantify individual-level preferences with national indices that capture health, pathogen prevalence, economic development and homicide rate. To address issues of multicollinearity among national demographic variables, we used an Independent Factors Analysis (IFA) to reduce number of country-level predictors. IFA is similar to PCA but allows factors to be correlated (i.e., not orthogonal), which can then be used as predictors in the fixed effects model. We used these data to test whether women’s preferences for facial masculinity were stronger under conditions where survival is compromised via pathogen prevalence and selecting a masculine mate may indirectly enhance offspring survival33,34,35. We also tested two alternative hypotheses that women’s facial masculinity preferences may be stronger under conditions where male survival is impacted by homicide rates38 or under conditions of high population density and wealth41. Finally, we asked whether variation in women’s sexual openness predicts their facial masculinity preferences.