Indirect (genetic) benefits to offspring have been proposed as a mechanism for why certain traits are preferred in a partner; however, whether this mechanism plays a role in humans is currently debated. In this thesis, I aim to address whether women’s preference for masculinity is due to indirect benefits, which according to the predominant theory is preferred by women for heritable benefits in immune functioning of offspring.
Before I present the empirical findings of this thesis, I first give an overview of the evolutionary approach to human mating and describe sexual selection mechanisms that may drive preference for a trait and review the literature on human mate preference for sexual dimorphism (i.e., the masculinity of males and the femininity of females). The thesis is then separated into two parts:
In Part 1, I present three studies that investigate the relationship between contextual factors and mate preferences. In Study 1, we tested whether individual pathogen avoidance and resource scarcity predicted revealed mate preferences for facial attractiveness, facial sexual dimorphism, and perceived intelligence based on 689 participants’ attractiveness ratings of manipulated online dating profiles. Supporting our predictions, pathogen disgust positively predicted men and women’s preferences for facial attractiveness and men’s preference for facial femininity, whereas women’s resource scarcity negatively predicted their preference for facial masculinity. Contrary to previous results, pathogen disgust was not associated with women’s facial masculinity preferences, and unexpectedly, neither pathogen disgust nor resource scarcity predicted preference for greater perceived intelligence. In Study 2, we investigated the association between women’s pathogen disgust and facial masculinity preferences further by extending previous research that is solely based on young adult participants and targets, using forced-choice preference measures, begging the question as to whether the findings are generalisable to other adult age groups or other preference measures. We conducted three experiments assessing facial masculinity preferences of women of a wider age range rating target faces of a wider age range than previously investigated. In Experiment 1 and 2, 447 and 433 women respectively made forced choices between two identical faces that were manipulated on masculinity/femininity. In Experiment 1, face stimuli were manipulated on sexual dimorphism using age-matched templates, while in Experiment 2 young face stimuli were manipulated with older templates and older face stimuli were manipulated using young templates. In Experiment 3, the facial masculinity preferences of 386 women were revealed through their attractiveness ratings of natural (unmanipulated) faces. For Experiment 1, no association was found between women’s pathogen disgust and masculinity preference, but when limiting the sample to younger women rating younger faces we replicated previous findings of significant association between pathogen disgust and preference for facial masculinity. Results for Experiment 2 and Experiment 3 found no effect of pathogen disgust sensitivity on facial masculinity preferences regardless of participant and stimuli age. In Study 3, across two experiments we investigated the effects of pathogen prevalence and resource scarcity on specific body dimensions, such as women’s waist size, waist-to-hip-ratio (WHR), men’s shoulder-to-hip ratio (SHR), and body mass index (BMI), all of which have also been theorised to be associated with health benefits or ability to deal with resource scarcity. Experiment 1 found that pathogen disgust negatively influenced men’s WHR preference in female bodies, while SES was negatively associated with women’s SHR and BMI preferences in male bodies. Experiment 2 found that pathogen disgust negatively predicted men’s WHR preference, and positively predicted women’s SHR preference, while SES negatively predicted men’s WHR preference.
In Part 2 of this thesis, I assess the role of genetics on facial masculinity and preference for facial masculinity using biometrical modelling across two studies. In Study 4 we test for genetic variation in women’s preference for facial masculinity using a large sample of identical and non-identical twins and their siblings (N = 2175). We found that 38% of variance in facial masculinity preference could be attributed to genes. In contrast, we found no significant association of masculinity preference with cycle phase (N = 574), or pathogen disgust or self-rated attractiveness (N = 2175), while sociosexuality showed a significant but weak association (<1% of variance; N = 2174). In Study 5, we assess crucial assumptions of the predominant theory, namely that variation in facial masculinity is due to genetic variation and that genetic factors that increase male facial masculinity do not increase facial masculinity in female relatives. We objectively quantified the facial masculinity in photos of identical (n = 411) and nonidentical (n = 782) twins and their siblings (n = 106). Using biometrical modeling, we found that much of the variation in male and female facial masculinity is genetic. However, we also found that the masculinity of male faces is unrelated to their attractiveness and that facially masculine men tend to have facially masculine, less-attractive sisters.
In the final section of this thesis, I discuss the implications of my research on current theories of human mate preferences. Overall, findings from this thesis provide converging evidence that challenges the predominant theory that masculinity is preferred in a partner due to heritable immunocompetence benefits to offspring.