Mandibular gracilization through time: a 3D comparison of ancient and contemporary populations

Abstract

Understanding the evolution of mandibular morphology provides key insights into the interplay between diet, technology, and oral health. When human populations made the subsistence transition from hunter-gathering to agriculture, the diet softened, and mandibles became more gracile. In this study, we compare the mandibular morphology of agricultural populations from ancient Sudan (350 BCE-350 CE) to contemporary Floridian populations to explore how jaw shape differs across geographic and temporal ranges beyond the agricultural revolution. We hypothesized that contemporary Floridian mandibles would differ significantly in shape from those of ancient agricultural populations, reflecting a continued trend of mandibular gracilization. Specifically, we predicted that the ancient mandibles would be more robust, with wider rami, shorter vertical height, and more acute body-ramus angles consistent with greater masticatory muscle use. To test this hypothesis, 39 contemporary mandibles were 3D surface scanned and compared to 38 ancient mandibles using 3D geometric morphometric quantitative methods, including a Procrustes ANOVA. Our predictions were met, and our hypothesis was supported (p = 0.001). Contemporary mandibles are characterized as being more gracile with taller and narrower rami and more obtuse gonial angles. This is likely due to the softness of the contemporary diet, perhaps driven by the recent rise in ultra-processed foods. Our findings demonstrate that mandibular shape can undergo significant change over a 2,000-year span, even between geographically distinct populations, and that contemporary gracilization parallels the morphological shifts associated with the earlier transition from hunter-gathering to agriculture.