Sexual Dimorphism in the Facial Morphology and Skin Color in Sub-Saharan Africa

In human faces, sexual dimorphism manifests itself in both morphological traits and skin color differences between males and females. Existing research has focused mainly on facial shape, but less is known about the interplay between dimorphism in facial structure and skin color, particularly in African populations. We investigated the degree of sexual dimorphism in facial shape and skin color in four sub-Saharan African populations (Cameroon, Mauritania, Senegal, and Sudan) using geometric morphometric analyses. We examined whether masculinization of facial morphology was consistently associated with darker skin tones, as would be expected given the influence of sex hormones on pigmentation, or whether this relationship varied across populations. Sexual dimorphism varied significantly in both shape and color across populations. The Sudan sample exhibited the strongest shape dimorphism in facial structure, while the Cameroonian and Mauritanian samples showed less pronounced differences. In contrast, the Senegal sample demonstrated the highest dimorphism in skin color, with men being notably darker than women. An unexpected pattern emerged in the Cameroonian and Mauritanian samples, where the most morphologically masculine men had a lighter skin than their less facially masculine peers. This challenges the expectation of skin darkening with increased masculinization. Given the drawbacks of highly masculine appearance, we discuss a possible compensatory mechanism where highly masculinized men have a lighter skin to offset the social or reproductive costs associated with morphological hypermasculinity. Our findings highlight the complexity of sexual dimorphism in African populations, emphasizing the need for further research into the impact of evolutionary, genetic, and sociocultural factors on facial diversity.