Abstract
Facial width-to-height ratio (fWHR) has been proposed as a sexually dimorphic signal in humans that develops under the influence of pubertal testosterone (T); however, no studies have examined the association between fWHR and T during the phase in which facial growth is canalized—adolescence. In a sample of adolescent Tsimane males, we evaluate the relationship between T, known T-derived traits (i.e. strength and voice pitch), and craniofacial measurements. If fWHR variation derives from T’s effect on craniofacial growth during adolescence, several predictions should be supported: 1) fWHR should increase with age as T increases, 2) fWHR should reflect adolescent T (rather than adult T per se), 3) fWHR should exhibit velocity changes during adolescence in parallel with the pubertal spurt in T, 4) fWHR should correlate with T after controlling for age and other potential confounds, and 5) fWHR should show strong associations with other T-derived traits. Only prediction 4 was observed. Additionally, we examined three alternative facial masculinity ratios: facial width/lower face height, cheekbone prominence, and facial width/full face height. In contrast to fWHR, all three alternative measures show a strong age-related trend and are associated with both T and T-dependent traits. Overall, our results question the status of fWHR as a sexually-selected signal of pubertal T and T-linked traits.
Highlights
Animals have evolved mechanisms to detect, decode, and act on signals conveying fitness-relevant information about others [1]
By targeting an adolescent population, we address a corollary issue in the study of facial masculinity: Masculinity is usually operationalized by dimensions that differ between adult males and females; in the literature on facial shape, “masculinity” is often de facto defined in a way that is dependent on male facial growth trajectories, and on female facial growth trajectories (e.g. [52,53]; cf. [54])
Zero-order correlations showed that facial width-to-height ratio (fWHR) is not positively associated with age (r = -0.03, ns) nor with T (r = 0.13, ns) during male adolescence
Summary
Animals have evolved mechanisms to detect, decode, and act on signals conveying fitness-relevant information about others [1]. In support of this correlational premise, a number of studies have found associations between adult men’s fWHR and perceived likelihood of aggression, dominance, and prosocial behavior [17,18,19,20,21,22]; actual rates of aggressive and prosocial behaviors [23,24,25,26,27]; success in athletics, politics, and business [17,12,28,29,30,31,32]; and with T itself [16] These behavioral traits (i.e., aggressive and other social behaviors) are linked to T [33,34,35] and are sexually dimorphic themselves [36,37], supporting the notion that fWHR may be affected by T as well, and provide useful predictive information about other T-associated traits. These relationships should survive controls for potential spurious variables, such as adiposity and height
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