From 2020... When two sexually dimorphic androgen dependent facial traits are judged in concert, ornamental (facial hair) rather than structural masculine facial features (bones) underpin men’s intra-sexual judgments of formidability

Multivariate Intra-Sexual Selection on Men’s Perceptions of Male Facial Morphology. Valeriya Mefodeva, Morgan J. Sidari, Holly Chau, Brett Fitzsimmons, Gabrielle Antoine, Tessa R. Clarkson, Samuel Pearson, Anthony J. Lee & Barnaby J. W. Dixson. Adaptive Human Behavior and Physiology volume 6, pages143–169, Mar 17 2020. https://link.springer.com/article/10.1007%2Fs40750-020-00128-2

Abstract

Objectives: Intra-sexual selection has shaped the evolution of sexually dimorphic traits in males of many 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 intra-sexual judgments of formidability.

Discussion

A growing body of research implicates intra-sexual selection in shaping the evolution of men’s secondary sexual traits, dominance, and status seeking (Lukaszewski et al. 2016; Puts 2010; Rosenfield et al. 2020). The current study reports men’s ratings of masculinity, dominance, and aggressiveness for male faces increased linearly with craniofacial masculinity, being lowest for the least masculine faces and highest for the most masculine faces. Beards were also judged as more masculine, dominant, and aggressive than clean-shaven faces. However, the effects of craniofacial masculinity on judgments of male faces were dwarfed by the effect of facial hair, such that ratings for masculinity, dominance, and aggressiveness were higher at each level of facial masculinity for bearded compared to clean-shaven faces. Our findings replicate previous studies reporting that beards exert stronger effects than facial masculinity on judgments of men’s masculinity and dominance (Dixson et al. 2017c; Sherlock et al. 2017). As an example of the size of these effects, we report significantly higher ratings (all ps < .001) for bearded faces with very feminine facial shape over the most masculine clean-shaven faces for ratings of masculinity (d = .61), dominance (d = .45), and aggressiveness (d = .38), highlighting that facial hair potentially enhances male intra-sexual formidability through amplifying underlying masculine craniofacial features such as jaw width, facial length and width.

Converging evidence demonstrates that men’s facial masculinity predicts men’s intra-sexual formidability (Puts 2010; Sell et al. 2012). Men with more masculine faces have greater upper body strength (Fink et al. 2007; Windhager et al. 2011), fighting ability (Třebický et al. 2013, 2015, 2018; Zilioli et al. 2015), and higher mating success (Hill et al. 2013; Kordsmeyer et al. 2018) than less facially masculine men. The degree to which men are sensitive to other men’s secondary sexual traits, including facial masculinity, when assessing their dominance may vary due to their own physical and psychological dominance (Puts 2010; Sell et al. 2012; Watkins et al. 2010a, b). In the current study, we did not find that men high in social dominance (Hypothesis 1) or status seeking (Hypothesis 3) were less sensitive to facial masculinity when ranking male facial masculinity, dominance, or aggressiveness than less dominant men (Watkins et al. 2010b). We also tested whether men’s physical masculinity was negatively associated with their judgments of facial masculinity (Hypothesis 7). Thus, height is positively associated with men’s social dominance (Puts 2010), aggressiveness (Archer 2009), and fighting ability (Sell et al. 2012). While we found that height was negatively associated with judgments of male masculinised and feminised faces for ratings of masculinity, dominance, and aggressiveness, the significant interaction was driven by lower ratings for feminised rather than masculinised faces. This provides partial support that taller men are less sensitive to cues of facial dominance in male faces, but does not directly replicate past findings that height is negatively associated with dominance judgments for male facial masculinity (Watkins et al. 2010a). We also found that participants with higher self-reported facial masculinity gave higher ratings of dominance, masculinity, and aggressiveness. However, there were no associations between self-reported facial masculinity and self-reported social dominance, assertiveness, or success and dedication on men’s judgments of male facial masculinity.

Facially masculine men report more open sociosexualities (Boothroyd et al. 2008), greater interest in short-term relationships (Arnocky et al. 2018), having more short-term partners (Rhodes et al. 2005), and greater likelihood of poaching other men’s partners (Rhodes et al. 2013). Thus, men with more masculine faces and better developed secondary sexual characters may be less jealous of masculine looking men than their less masculine contemporaries. Indeed, previous research has shown that men’s height is negatively associated with their self-reported intra-sexual jealousy (Buunk et al. 2008). While we also found that taller men reported lower intra-sexual jealousy (r = −.279), we did not find that taller, more facially masculine, or bearded men were less jealous of facial masculinity in male faces. Instead, participants reporting lower intra-sexual jealousy rated clean-shaven and less masculine faces as less masculine, dominant, and aggressive than masculine or bearded faces. This could simply reflect that men attribute lower threat in mating contexts to less masculine and physically formidable looking men. However, with regards men’s intra-sexual jealousy and judgments of beardedness, to our knowledge the only study measuring associations between women’s sexual openness and attractiveness ratings of male facial hair reported a positive association between female sexual openness and preferences for beards (Stower et al. 2019). At present, there are no published data relating beardedness to men’s sociosexuality and whether the decision to wear facial hair is a reflection of men’s sociosexual attitudes is an important question for future research.

Compared to the body of research on intra-sexual selection and judgments of male facial masculinity, fewer studies have assessed individual differences in men’s dominance and their judgments of male beardedness. Past research has shown that bearded men reported higher aggressive sexism scores than clean-shaven men in the U.S.A and India (Oldmeadow and Dixson 2016), but not Sweden (Hellmer and Stenson 2016; Hellmer et al. 2018). Men with facial hair report feeling more masculine (Wood 1986) and had higher serum androgens (Knussman and Christiansen 1988) than men favouring a clean-shaven appearance. In the current study, self-reported beardedness was positively associated with self-perceived facial masculinity (r = .158) and self-reported dominance (r = .119). Participants who reported higher scores on dominance and assertiveness personality scales also gave significantly higher masculinity, dominance, and aggressiveness ratings to bearded but not clean-shaven faces compared to participants lower in dominance and assertiveness. These findings complement growing evidence that beards enhance intra-sexual communication of masculine social dominance (Craig et al. 2019; Dixson and Vasey 2012; Dixson et al. 2017c) and provide the first evidence that facial hair is positively associated with male self-perceived social dominance. Importantly, this correlation cannot determine whether socially dominant men choose to grow their beards or whether keeping a beard augments men’s self-reported social dominance due to positive social feedback from peers. There is some evidence that bearded men have higher mating success when sex ratios are more male-biased (Barber 2001) and that beards (and female preferences for them) are more common in larger cities, with low average incomes and high life expectancies (Dixson et al. 2017a). Future research exploring the causal effects of men’s grooming decisions on social dominance and mating success would be valuable.

Comparative research among nonhuman animals can shed light on the roles of facial masculinity and beards in intra-sexual communication. Researchers working on nonhuman animals distinguish between the role of male weaponry and ornamentation in intra-sexual competition, such that weapons are employed during direct physical confrontations whereas ornaments communicate status and dominance without necessarily being associated with physical formidability (McCullough et al. 2016). Weapons involved in direct competition and fights are rarely false signals of male quality (Berglund et al. 1996) and may augment attractiveness to females when selecting for males bearing direct benefits (Wong and Candolin 2005). Our results failed to support several past studies that found associations between men’s intra-sexual competitiveness and judgments of male facial masculinity. This was surprising as masculine facial structure is positively associated with men’s upper body strength (Fink et al. 2007; Windhager et al. 2011), muscularity (Holzleitner and Perrett 2016), stature (Zaidi et al. 2019) and fighting ability (Třebický et al. 2015; Zilioli et al. 2015). Mixed martial arts fighters with more masculine facial features are more often winners than less facially masculine fighters (Třebický et al. 2015; Zilioli et al. 2015) and fighters with greater anaerobic fitness are rated as better fighters (Třebický et al. 2018). Our results may have differed had we included more interactive behavioural paradigms rather than comparisons of self-report measures of dominance. For example, recent research in which men were assigned to compete in either violent or non-violent video games revealed that men who competed in violent video games were slower to retreat from a hypothetical physical confrontation with a masculine looking male, and were slower to recognise threatening facial expressions than participants in competing in non-violent video games (Denson et al. 2020). It may be beneficial to repeat our studies using more interactive experimental approaches to test whether psychologically and physically masculine men are less sensitive to masculine traits.

In contrast to sexually selected weapons, ornaments can communicate dominance without being directly involved in combat (McCullough et al. 2016). For example, in mountain gorillas (Gorilla beringei beringei) male dominance rank, success in male-male dyadic contests, and number of females in the social group is positively associated with cranial adipose crest size and back breadth (Wright et al. 2019). In some cases, weaponry may not reliably communicate physical formidability (Berglund et al. 1996). Thus, in male fiddler crabs (Uca mjoebergi) claw size is associated with attractiveness, resource holding, and in assessing fighting ability between rival males (Reaney et al. 2008). However, when males lose their claws during fights or due to predation the regrown claws are of similar size to their original claws but less robust, yet rival males are unable to discern weapon quality and overestimate their opponents fighting ability (Lailvaux et al. 2009). Similarly, male slender crayfish (Cherax dispar) with larger claws successfully dominate males with small claws despite any positive association between their claw size and muscle development (Wilson et al. 2009). Beardedness is possibly the most sexually dimorphic of men’s secondary sexual characters (Dixson et al. 2005; Grueter et al. 2015) and enhances ratings of age, masculinity, dominance, and aggressiveness by enlarging the size of the jaw (Dixson et al. 2017c), the midface (Sherlock et al. 2017) and the saliency of agonistic expressions (Dixson and Vasey 2012; Craig et al. 2019). However, facial hair is unlikely to reflect aspects of male fighting ability (Dixson et al. 2018a) and may serve to enhance perceptions of masculinity, dominance, and aggressiveness to curtail intra-sexual conflicts from escalating into costly physical contests. Future research investigating whether bearded men are more successful than their clean-shaven counterparts in social rather than physical forms of intra-sexual competition would be valuable. Presently, our study provides some support for a role of intra-sexual selection in men’s judgments of male facial masculinity and reports the first data on individual differences in men’s judgments of male facial hair, which suggest beards are intra-sexually selected badges of status.