Previous studies suggest that environmental variables differentially affect male and female body size, resulting in decreased sexual size dimorphism in samples under stressed conditions. In contrast, research investigating the relationship between living conditions and craniofacial trait dimorphism is lacking. Given that craniofacial traits are not costly to maintain and play a significant role in mate preferences, dimorphism may be expected to either remain constant under stressed conditions, or possibly increase due to greater sexual selection pressures.

This study tests for systematic effects of living conditions on human sexual dimorphism by comparing male and female differences in body size and two specific cranial traits, the browridge and chin, across an array of diverse populations (13 samples, n = 669). Genetically similar, yet environmentally varied paired samples were included to better isolate the environmental effects from population differences. Postcranial size dimorphism was calculated using traditional osteometric methods. In order to analyze sexual dimorphism in browridge and chin morphologies, these features were objectively isolated from 3D surface scans, and transect and semilandmark data were extracted for morphometric analyses.

Results suggest that within populations, stature dimorphism systematically decreases in more environmentally stressed samples. In support of the female buffering hypothesis, males displayed greater environmental sensitivity than females.

Sexual dimorphism in browridge morphology also generally decreased in more stressed samples. This is contrary to the hypothesized pattern and suggests that environmentally driven mate selection pressures may not be responsible for observed variations in browridge dimorphism. Furthermore, results indicate that within-population variations in browridge morphology are not the result of any allometric effects of body size or related to mandibular strengths. Sexual dimorphism in chin morphologies did not follow any consistent trends with living conditions and was not correlated with body size. While some significant relationships were observed between chin variables and mandibular strengths, no consistent relationships were observed across all sex/population groups. No significant correlations were observed between brow and chin morphologies;​ thus, individuals that display more “masculine” browridges do not display more “masculine” chins. Overall, these results suggest that sexual dimorphism in body size, browridge, and chin morphologies are likely under different selection pressures.