Facial and body sexual dimorphism are not interconnected in the Maasai

Abstract

Background In this paper, we investigate facial sexual dimorphism and its’ association with body dimorphism in Maasai, the traditional seminomadic population of Tanzania. We discuss findings on other human populations and possible factors affecting the developmental processes in Maasai. Methods Full-face anthropological photographs were obtained from 305 Maasai (185 men, 120 women) aged 17–90 years. Facial shape was assessed combining geometric morphometrics and classical facial indices. Body parameters were measured directly using precise anthropological instruments. Results Sexual dimorphism in Maasai faces was low, sex explained 1.8% of the total shape variance. However, male faces were relatively narrower and vertically prolonged, with slightly wider noses, narrower-set and lower eyebrows, wider mouths, and higher forehead hairline. The most sexually dimorphic regions of the face were the lower jaw and the nose. Facial width-to-height ratio (fWHR), measured in six known variants, revealed no significant sexual dimorphism. The allometric effects on facial traits were mostly related to the face growth, rather than the growth of the whole body (body height). Significant body dimorphism was demonstrated, men being significantly higher, with larger wrist diameter and hand grip strength, and women having higher BMI, hips circumferences, upper arm circumferences, triceps skinfolds. Facial and body sexual dimorphisms were not associated. Conclusions Facial sex differences in Maasai are very low, while on the contrary, the body sexual dimorphism is high. There were practically no associations between facial and body measures. These findings are interpreted in the light of trade-offs between environmental, cultural, and sexual selection pressures.

Cross-Cultural Differences in Perception of Facial Trustworthiness Based on Geometric Morphometric Morphs

“…In Buryats, trustworthy-looking faces had less prolonged upper face, and thus had higher upper fWHR (although the differences in fWHR between trustworthy- and untrustworthy-looking Buryat faces did not reach statistical significance). In contrast to the human populations studied so far (of both African, Asian, and European descent), where fWHR is either higher in men, or does not demonstrate sex differences (see Rostovtseva et al, 2021b, and references therein, as well as Butovskaya, Rostovtseva, & Mezentseva, 2022; Caton & Dixson, 2022; Hodges-Simeon et al, 2021; Özener, 2012), in Buryats high fWHR is a female-specific facial feature, which was demonstrated in earlier studies conducted in this population (Rostovtseva et al, 2021b; Rostovtseva, Mezentseva, et al, 2020). Our results clearly indicate that perception of male facial trustworthiness within the same sex is closely related to facial masculinity features, with masculine faces perceived as less trustworthy.…”

“…It is well established that facial appearance as well as patterns of facial sexual dimorphism vary across human populations (Butovskaya, Rostovtseva, & Mezentseva, 2022; Kleisner et al, 2021; Mezentseva et al, 2023). Literature data also suggest that cross-cultural facial perception differs to some extent from that of within-cultural.…”

Facial cues to physical strength are not always associated with facial masculinity: Comparative study of Europeans and Southern Siberians

“…Human facial morphology is also subjected to considerable sexual dimorphism, which is explained by a number of developmental processes, including exposure to sex hormones, testosterone and its metabolites. Adult men at the cross‐population level generally have relatively lower forehead height, more vertically prolonged faces with greater height of the lower jaw, and relatively higher nasal width, compared to women (Butovskaya et al, 2022; Kleisner, Tureček, et al, 2021; Rostovtseva et al, 2021; Tanikawa et al, 2021).…”

“…Although sex‐specific facial morphology demonstrates certain degree of universality, some sexually‐dimorphic traits are still subjected to population variations. For instance, in some Asian and African (the Maasai) populations, against the background of generally larger absolute sizes of male faces, women tend to have higher relative widths of the lower jaw (bigonial width) (Butovskaya et al, 2022; Rostovtseva et al, 2021; Tanikawa et al, 2016). In contrast, in European populations, higher relative lower jaw width is a male‐specific feature (Fink et al, 2005; Rostovtseva et al, 2023).…”

“…It may be concluded that association between HGS and facial shape is similar in populations of different origin. At the same time, the Maasai case (Butovskaya et al, 2018, 2022) indicates that the association between handgrip strength and facial morphology does not always corresponds to the direction of facial sexual dimorphism.…”