A geometric morphometric study of sexual dimorphism in the crania of indigenous southern Africans

Much of our understanding of sexual dimorphism in the crania of Bantu-speaking southern Africans is based on traditional morphometric analyses. The purpose of this study is to use geometric morphometric methods to demonstrate new, and clarify and confirm previously described, morphological features related to sexual dimorphism. A total of 332 (182 male and 150 female) southern African crania were studied. The three-dimensional coordinates of 96 landmarks were analysed using the shape analysis software morphologika. Generalized Procrustes analysis was used to register the landmark data and principal components analysis was performed to explore the shape variation between the male and the female crania. Dimorphic cranial shape features found include relative 'bizygomatic breadth', the profile of the forehead contour, the form of the supramastoid crest, alveolar prognathism, and the size of the posterior airway space. These features appear to be related to cranial size, muscle development, and to different male-female energy requirements. Geometric morphometric methods are shown to be a most useful tool for demonstrating and quantifying morphological shape differences between male and female crania. Further, we demonstrate how the techniques used can be applied to problems in physical and forensic anthropology with increased sensitivity and objectivity compared to traditional methods.