Constancy of Sexual Dimorphism in the Infracranial Skeleton.

Sexual dimorphism in the human infracranial skeleton has been extensively studied, yet its structural organization across skeletal regions remains incompletely characterized at a global scale. Using a geographically diverse sample of 3177 individuals of known sex (1219 females; 1958 males) drawn from five documented skeletal collections, this study quantifies sexual dimorphism across 12 long bones measurements of the humerus, radius, femur, and tibia. Dimorphism indices (DS%), two-way ANOVAs with partial η2, Mahalanobis distances, Hedges' g, and D-index were computed to characterize the magnitude and the consistency of sex differences across groups. Results reveal a clear anatomical gradient in the expression of sexual dimorphism. Maximum bone lengths exhibit the lowest dimorphism (DS% = 8.5%-11.5%) with high stability and low within-sex variability. Articular breadths show the strongest association with sex (partial η2 > 56%) combined with relatively low intra-sexual dispersion. Diaphyseal diameters, particularly in the upper limb, display the highest DS% values but also the greatest coefficients of variation, reflecting greater biomechanical and methodological sensitivity. Sex × Group interactions are weak or non-significant across all variables, and rank concordance analyses confirm that this hierarchical pattern is consistent across populations (Kendall's W = 0.707-0.814, p < 0.001). These findings strongly support previous studies demonstrating the reliability of articular breadths for sex estimation in skeletal remains, and confirm that the metric signal of sexual dimorphism in long bones reflects a fundamental and broadly shared structural organization of the human appendicular skeleton.