Associations of physical strength with facial shape in an African pastoralist society, the Maasai of Northern Tanzania

Human face as a biosocial marker in human evolution

In this article, we provide an analytical review of contemporary perspectives on the role of the human face in the system of communication and human evolution. We explore how the human face has developed throughout our evolutionary history under the influence of ecological and social processes considered in the framework of self-domestication. A significant focus of the article is the relationship between facial morphology - which serves as an important signal in human communication - and the behavioural traits that have been vital to our species' evolution. We also examine how people perceive the faces of others, the information conveyed through facial features, and the evolutionary mechanisms that have shaped the human face as a biosocial marker. As a complement, we briefly discuss the evolution of emotional facial expressions, highlighting their importance as a key channel of non-verbal communication in humans. This article not only reviews current literature on these topics but also integrates findings from our own empirical research into the existing body of knowledge.

Violence exposure is associated with preference for masculine faces: evidence from Senegal

It has been suggested that in threatening environments, both women and men should prefer more masculine men as romantic and coalition partners, respectively. Empirical evidence for this hypothesis has been weak or inconsistent, primarily because most experimental research has focused on elevating the perceived danger from other men through virtual threats. This study investigates whether personal experience with violence predicts the preference for masculine features in 326 Senegalese participants presented with pairs of manipulated facial photographs of West African men (one more feminine, one more masculine) and asked to indicate which face is more attractive (to women) or more trustworthy (to men). The findings reveal a strong association between violence exposure and facial feature preferences. Those who experienced (particularly physical) violence showed a higher preference for masculinized faces (up to 95% in women, 82% in men) compared to the baseline (57% in women, 63% in men). This difference is proposed to reflect an adaptive strategy of prioritizing physical protection in settings with a higher incidence of violent confrontations. Much of the variance can be found between groups. The direct effect of experienced violence diminishes over time, which suggests a dynamic interplay between innate predispositions and environmental influences on aesthetic preferences.

Associations of Facial Shape With Physical Strength and 2D:4D in a Turkish Male and Female Sample

OBJECTIVE

Human sexual dimorphism in physical strength manifests itself in men having a greater muscle mass than women, reflecting ancestral roles in competition, protection, and provisioning. Prenatal testosterone exposure, approximated via the second-to-fourth digit ratio (2D:4D), is linked to increased muscular strength in both sexes, indicating a developmental influence. Previous research has shown that both physical strength and 2D:4D have facial shape correlates, especially in men, but most studies have focused on Western populations and one trait. We therefore hypothesized a broader relationship between facial shape and both physical strength and 2D:4D.

MATERIALS AND METHODS

In this study, we quantified the association between facial shape, handgrip strength (HGS), and 2D:4D in a non-Western Turkish sample (72 men, 55 women; Md = 22 y, SIR = 1.8 y) using two dimensional geometric morphometrics. Thirty-eight somatometric and 32 semi-landmarks were digitized on facial photographs taken in frontal view. Physical strength was assessed via handgrip strength (HGS), and the second digit length was divided by the fourth digit length to calculate 2D:4D.

RESULTS

Both HGS and 2D:4D were significantly associated with shape in both sexes, but only in men did they explain a significant amount of facial variation. Thin-plates spline deformation grids and geometric morphometric morphs visualized the facial shape changes related to variations in handgrip strength, 2D:4D, and sexual dimorphism, enabling trait comparisons.

CONCLUSION

This study contributes a comparative sample from the Middle East, which is indispensable to discern universalities from Western peculiarities. It provides evidence to better understand the biological basis of facial traits, which can potentially serve as increasingly relevant social cues in today's online and digital environments.

Male facial cues to physical strength in Europe: Medium-strength preference and higher aggressiveness attribution to the weakest

OBJECTIVES

The capacity to assess male physical strength from facial cues may be adaptive given health and fitness-related associations with muscular strength. Our study complements recent research on strength-related face perceptions of male Maasai by applying the protocol to male European faces and assessors.

METHODS

Five distinct facial morphs calibrated for handgrip strength (HGS) were manufactured with geometric morphometrics performing regressions of the Procrustes shape coordinates on HGS in a sample of 26 European men (18-32 years). Young adult men and women (n = 445) rated these morphs on physical strength, attractiveness, and aggressiveness.

RESULTS

Facial morphs calibrated to lower HGS were rated as less strong, less attractive, and more aggressive than those calibrated to higher HGS. Medium levels of HGS were associated with the highest attractiveness ratings.

CONCLUSIONS

The rating patterns of physical strength, attractiveness, and aggressiveness for European male facial morphs exhibit similarity to previous ratings of Maasai male faces. Therefore, the current findings corroborate the suggestion of a common mechanism for social attributions based on facial cues to physical strength, modulated by local ecology and societal context.

Cross-cultural perception of strength, attractiveness, aggressiveness and helpfulness of Maasai male faces calibrated to handgrip strength

Previous research has demonstrated that Maasai and Europeans tend to align in their ratings of the physical strength and aggressiveness of Maasai male faces, calibrated to hand grip strength (HGS). However, perceptions of attractiveness of these faces differed among populations. In this study, three morphs of young Maasai men created by means of geometric morphometrics, and depicting the average sample and two extrema (± 4 SD of HGS), were assessed by men and women from Tanzania, Czech Republic, Russia, Pakistan, China, and Mexico (total sample = 1540). The aim of this study was to test cross-cultural differences in the perception of young Maasai men's composites calibrated to HGS, focusing on four traits: physical strength, attractiveness, aggressiveness, and helpfulness. Individuals from all six cultures were able to distinguish between low, medium, and high HGS portraits. Across all study populations, portrait of Maasai men with lower HGS was perceived as less attractive, more aggressive, and less helpful. This suggests that people from diverse populations share similar perceptions of physical strength based on facial shape, as well as attribute similar social qualities like aggressiveness and helpfulness to these facial images. Participants from all samples rated the composite image of weak Maasai men as the least attractive.

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

OBJECTIVES

The aim of our study was to compare morphometric patterns of facial sexual dimorphism with strength-face relationship in members of two distinct populations of European and Central Asian origin: Russians and Tuvans.

METHODS

Handgrip strength (HGS) measures and facial photographs were collected from Russian (n = 233) and Tuvan (n = 187) men and women. We digitized 70 landmarks and semilandmarks on full-face and 54 landmarks and semilandmarks on profile photos. This was done to capture variation in facial morphology. After that, we performed the shape regressions of landmarks' coordinates upon sex and HGS. Results were visualized in forms of thin-plate deformation grids and geometric morphometric morphs.

RESULTS

In both populations, HGS was associated significantly with male facial shape only. In Russian men, strength-related changes of facial shape were almost completely in direction of increase in male-typicality. This was especially evident for the relative lower facial width, which was higher in men compared to women, as well as in stronger men compared to weaker ones. On the contrary, in Tuvans the lower face was relatively narrower in men than in women. However, the facial shape of strong Tuvan men was also associated with relatively wider lower face. Our results indicate that the effect of strength on facial shape is relatively independent of facial sexual dimorphism.

CONCLUSIONS

Our findings clearly demonstrate that physical strength is associated with the shape of the lower part of male faces even in populations with a mismatched direction of lower face sexual dimorphism.

Perception of strength, attractiveness and aggressiveness of Maasai male faces calibrated to handgrip strength: Evidence from a European sample

OBJECTIVES

Previous research showed that male and female members of the Maasai from Northern Tanzania judge images of facial morphs calibrated to greater handgrip strength (HGS) higher on strength and attractiveness, but lower on aggressiveness than those calibrated to lower HGS. The accurate assessment of male physical strength from facial information may be adaptive as suggested by the evidence on health and fitness-related benefits linked to high muscular strength.

METHODS

This study extends previous work by obtaining European female (n = 220) and male (n = 51) assessments of HGS-calibrated Maasai male faces. Participants rated five facial morphs for strength, attractiveness, and aggressiveness on computer screens.

RESULTS

Perceived physical strength increased with morphs calibrated to higher HGS. The lowest and highest HGS morphs were judged lower in attractiveness than the others, and rated aggressiveness decreased in morphs calibrated to higher HGS.

CONCLUSIONS

Given the high similarity between the current study findings and those previously reported from intra-population assessments of Maasai faces calibrated to HGS, we suggest that strength and aggressiveness perceptions of facial features associated with male physical strength may be universal. Attractiveness assessments of strength-related information in the faces of (very) strong men were less consistent across populations, possibly attributable to cultural and ecological contexts.

Demographic and sociocultural predictors of face image satisfaction: The U.S. Body Project I

Despite substantial literature surrounding how people process and perceive faces, there is very little research investigating how people evaluate their own faces. We examined how gender, body mass, race, age, and sexual orientation were linked to people's satisfaction with the appearance of their eyes, nose, facial shape, and face overall among 11,620 adults recruited via Mechanical Turk. Most people mostly or definitely agreed they were happy with their facial appearance. There were notable racial differences, with Asian participants tending to report greater dissatisfaction. For example, only 66% of Asian women and 60% of Asian men mostly or definitely agreed that they were happy with the appearance of their eyes, which was lower than other racial groups. BMI and age were not strongly associated with face satisfaction. Sexual minority men were less satisfied than heterosexual men. About one in four gay and bisexual men, compared to only one in seven heterosexual men, reported dissatisfaction with their overall facial appearance. Men and women with poorer face image engaged in more appearance surveillance, more strongly internalized the thin-ideal, and perceived stronger sociocultural pressures from peers, parents, and media. The current study highlights important sociocultural and demographic factors tied to poorer face image.

A meta-analysis of the association between male dimorphism and fitness outcomes in humans

Humans are sexually dimorphic: men and women differ in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone. Sexual selection hypotheses posit that, ancestrally, more 'masculine' men may have acquired more mates and/or sired more viable offspring. Thus far, however, evidence for either association is unclear. Here, we meta-analyze the relationships between six masculine traits and mating/reproductive outcomes (96 studies, 474 effects, N = 177,044). Voice pitch, height, and testosterone all predicted mating; however, strength/muscularity was the strongest and only consistent predictor of both mating and reproduction. Facial masculinity and digit ratios did not significantly predict either. There was no clear evidence for any effects of masculinity on offspring viability. Our findings support arguments that strength/muscularity may be sexually selected in humans, but cast doubt regarding selection for other forms of masculinity and highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.

Facial and body sexual dimorphism are not interconnected in the Maasai

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.

Perception of Emergent Leaders' Faces and Evolution of Social Cheating: Cross-Cultural Experiments

The aim of the present study was to investigate whether neutral faces of individuals with different propensities for leadership may convey information about their personal qualities, and are there impacts of sex, population and social environment on the facial perception. This study is based on a previous experiment ( Rostovtseva et al., 2022), where emergent leadership in the context of male group cooperation was investigated in Buryats (Mongolian population of Siberia). In the previous study three behavioural types of participants were revealed: non-leaders, prosocial leaders and leaders-cheaters, each having a set of distinguishing personality, communicative, and cooperative features. In the current study, three composite portraits representing different leadership qualities of Buryat men from the prior experiment were created. The composites were then scored on a number of traits by male and female Russian and Buryat independent raters (N = 435). The results revealed that ratings on masculinity, physical strength, dominance, competitiveness, and perceived leadership were positively correlated, while perceived trustworthiness was negatively associated with these traits. However, the composite portraits of actual leaders generally were scored as more trustworthy, masculine, and physically strong, with the prosocial leaders' portrait being perceived as healthier than others. Surprisingly, the composite of leaders-cheaters was scored as the most trustworthy and generous, and the least competitive than others. No significant effects of raters' sex, origin, or degree of familiarity with Mongolian appearance were revealed. We conclude that static facial morphology contributes to appearing trustworthy, which may allow exploitation of others.

Facial Cues to Physical Strength in Tuvans

This experimental study presents a comprehensive analysis of men’s and women’s facial traits signaling physical strength. The study was conducted among the Tuvans, in the populations from the southern and south-western regions of the Tuva republic. At the first stage of the study, we have identified the male and female facial traits which are objectively related to physical strength. According to the results of geometric and morphometric analysis, facial shape was associated with physical strength in both men (p <0.00) and women (p <0.00). Moreover, the facial areas associated with physical strength have a similar shape in men and women. In order to assess the ability of the Tuvans to recognize physical strength via facial images, we created portraits of men and women morphed according to the physical strength criterion and presented them for evaluation. The evaluators were Mangun-Taiga Tuvans of both sexes. The results showed that raters of the same origin, Mongun-Taiga Tuvans of both sexes, regardless of age, accurately recognize physical strength through men’s, but not women’s, portraits. The results obtained are discussed from the perspective of evolutionary theory.

Predicting strength from aggressive vocalizations versus speech in African bushland and urban communities

The human voice carries information about a vocalizer's physical strength that listeners can perceive and that may influence mate choice and intrasexual competition. Yet, reliable acoustic correlates of strength in human speech remain unclear. Compared to speech, aggressive nonverbal vocalizations (roars) may function to maximize perceived strength, suggesting that their acoustic structure has been selected to communicate formidability, similar to the vocal threat displays of other animals. Here, we test this prediction in two non-WEIRD African samples: an urban community of Cameroonians and rural nomadic Hadza hunter-gatherers in the Tanzanian bushlands. Participants produced standardized speech and volitional roars and provided handgrip strength measures. Using acoustic analysis and information-theoretic multi-model inference and averaging techniques, we show that strength can be measured from both speech and roars, and as predicted, strength is more reliably gauged from roars than vowels, words or greetings. The acoustic structure of roars explains 40-70% of the variance in actual strength within adults of either sex. However, strength is predicted by multiple acoustic parameters whose combinations vary by sex, sample and vocal type. Thus, while roars may maximally signal strength, more research is needed to uncover consistent and likely interacting acoustic correlates of strength in the human voice. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

Handgrip strength and 2D : 4D in women: homogeneous samples challenge the (apparent) gender paradox

The length ratio between the second and the fourth digit (2D : 4D) is a retrospective, non-invasive biomarker for prenatal androgen exposure. It was found to be negatively correlated with handgrip strength (HGS) in men, but the evidence for women is mixed. Such studies in women call for increased detection sensitivity. The present study was designed to reduce potential confounding factors, especially age and ethnicity variation. We measured the digit ratios and HGS of 125 healthy women between 19 and 31 years of age from a remote region in Austria. 2D : 4D of both hands was significantly and negatively correlated with HGS (n = 125, right hand: r = -0.255, p = 0.002, left hand: r = -0.206, p = 0.011). Size, direction and significance of correlation coefficients remained stable when statistically controlling for age, body weight, body height, body mass index or hours of exercise per week. This yields theory-consistent evidence that HGS and 2D : 4D are clearly associated in women-when sufficiently reducing genetic variation (confounding 2D : 4D), the ontogenetic environment and age ranges (confounding HGS) in the study population. This finding implies similar organizing effects of prenatal androgens as in men, pointing to a more parsimonious developmental mechanism and a new look into its proximate and ultimate causes.

Cross-cultural perception of female facial appearance: A multi-ethnic and multi-centre study

Humans extract and use information from the face in assessments of physical appearance. Previous research indicates high agreement about facial attractiveness within and between cultures. However, the use of a narrow age range for facial stimuli, limitations due to unidirectional cross-cultural comparisons, and technical challenges have prevented definitive conclusions about the universality of face perception. In the present study, we imaged the faces of women aged 20 to 69 years in five locations (China, France, India, Japan, and South Africa) and secured age, attractiveness, and health assessments on continuous scales (0-100) from female and male raters (20-66 years) within and across ethnicity. In total, 180 images (36 of each ethnicity) were assessed by 600 raters (120 of each ethnicity), recruited in study centres in the five locations. Linear mixed model analysis revealed main and interaction effects of assessor ethnicity, assessor gender, and photographed participant ("face") ethnicity on age, attractiveness, and health assessments. Thus, differences in judgments of female facial appearance depend on the ethnicity of the photographed person, the ethnicity of the assessor, and whether the assessor is female or male. Facial age assessments correlated negatively with attractiveness and health assessments. Collectively, these findings provide evidence of cross-cultural variation in assessments of age, and even more of attractiveness, and health, indicating plasticity in perception of female facial appearance across cultures, although the decline in attractiveness and health assessments with age is universally found.

Second-to-fourth digit ratio and facial shape in Buryats of Southern Siberia

BACKGROUND

The 2nd-to-4th digit ratio (2D:4D) is a putative predictor of a prenatal exposure to sex hormones. 2D:4D is sexually dimorphic (males < females). Studies, linking digit ratio and full facial shapes among Europeans, show that a low 2D:4D is associated with a set of male-specific facial features. Buryats - Mongolian people from Southern Siberia - demonstrate a different pattern of facial sexual dimorphism than Europeans (narrower and more vertically elongated faces in men as opposed to women).

AIM

The aim of the present study was to investigate the association between facial shape and the 2D:4D in comparison to the pattern of facial sexual dimorphism in Buryats.

SUBJECTS

Buryats: 88 men and 80 women aged 20 ± 2 years.

OUTCOME MEASURES

To assess relationship between facial shape and 2D:4D we used a geometric morphometric approach based on standardized full-face frontal photographs and direct measurements of the digit lengths among right-handed individuals.

RESULTS

The results revealed that 2D:4D was associated with facial morphology in Buryat men, and to a lesser extent in women. Narrower faces, elongated in the vertical direction, and a narrower lower facial outline, were characteristic of Buryat men with low 2D:4D ratios, which corresponded to the male-like facial shapes in Buryats.

CONCLUSIONS

In Europeans, such facial features were reported for men with a high 2D:4D, which corresponded more to female-like European facial shapes. Hence, our results show that sex-specific morphogenesis in humans is multidirectional, and that digit ratio is capable of predicting sex-specific facial traits even in populations with differing sexually-dimorphic morphology.

Sexual dimorphism in facial shape of modern Buryats of Southern Siberia

OBJECTIVES

The aim of the present study was to investigate sexual dimorphism in the full facial shape of modern Buryats-people of Southern Siberia of Mongolian origin.

METHODS

For this purpose, we have used geometric morphometrics based on standardized full-face frontal photographs. This allowed us to assess and visualize differences in facial shapes between Buryat men (n = 98) and women (n = 89). To specify the facial areas, where the differences occurred, we have complemented our analysis with standard anthropometric facial parameters based on approximations to the craniofacial and mandibular landmarks and soft-tissue morphology of specific facial areas.

RESULTS

Our results revealed that Buryat women have a set of sexually dimorphic features similar to those reported earlier for other Asian populations (a relatively wider and vertically shorter lower face, more round visible areas of the eyes, relatively narrower noses, smaller mouths, larger [in vertical dimension] foreheads, and relatively thinner upper lips, when compared to Buryat males). At the same time, Buryat women had a specific characteristic, distinguishing them from other world populations-a significantly higher upper face width-to-height ratio (fWHR) compared to males. This indicates that the high fWHR is not a universally male feature in humans, which raises a question of underlying developmental mechanisms.

CONCLUSIONS

Our results clearly demonstrate that some elements of sexually dimorphic facial shapes may differ across populations with different genetic and ecological backgrounds, and suggest that universal mechanisms of sex-specific facial morphogenesis still need to be clarified in the future.

Assessment of physical strength from gait: data from the Maasai of Tanzania

In industrialized societies, male gait provides information about physical strength. Male physical strength may be used by men and women to assess the fighting ability of rivals and the quality of potential mates, respectively. Women more than men discriminate between strong and weak walkers when assessing gait attractiveness. We presented videos of British men's gait-pre-categorized into strong and weak walkers-to male and female members ( n = 100) of the traditional Maasai in northern Tanzania in Africa. Maasai men and women judged the gaits of physically strong men less attractive than those of weak men and judged strong walkers to be weaker than weak walkers. These findings counter results from industrialized societies where participants accurately assessed strength from gait, thus arguing against a universal perception of physical strength from gait information.