Geometric morphometric analysis of facial sexual dimorphism in a contemporary sample : An application to sex prediction of ancient human remains

Abstract

Focusing on craniofacial bones, this study investigates morphological variation related to sexual dimorphism in order to deepen our understanding of human biological diversity and to provide new data from a contemporary reference sample. Accordingly, the research was guided by three objectives (i) identify the facial regions exhibiting the greatest sexual dimorphism using landmark-based geometric morphometric method; (ii) evaluate the reliability of discriminant models based on these dimorphic regions; and (iii) conduct exploratory analyses to assign sex classification probabilities to ancient subjects using the discriminant models derived from a contemporary reference sample. The reference sample comprised 44 skulls from subjects of known sex who died in 2024. The ancient sample included 4 skulls recovered from the Grotte de La Medecine (France), attributed to the chalcolithic period. Fourteen facial landmarks were digitized using 3DSlicer. Generalized Procrustes Analysis was performed to extract shape variables and standardized coordinates for statistical analysis. Thin -Plate Spline transformations quantified and visualized deformation amplitudes between the female and male shapes. Landmarks in the orbital showed the highest deformation amplitudes. Goodall F-test comparing male and female shapes across three facial regions revealed significant sexual dimorphism only in the orbital region and the global facial shape. Discriminant analysis demonstrated that the orbital region provided the highest classification accuracy (88.6%) compared to the global facial region (72.7%). The discriminant models yielded high probabilities of male and female sex classification for the ancient subjects. Using a reproducible method, comparable levels of accuracy to those reported in the scientific literature were achieved despite a relatively modest sample size. These findings further confirm the significant role of the orbital region in human craniofacial sexual dimorphism.