Molar crown thickness, volume, and development in South African Middle Stone Age humans

One highly debated issue in paleoanthropology is that of modern human origins, particularly the issue of when 'anatomically modern humans' (AMH) from the African Middle Stone Age became fully modern. While studies of cranial and external dental morphology suggest a modern transition occurred 150 000-200 000 years ago, little is known about dental development or enamel thickness in AMH. Studies of early members of the genus Homo suggest that the modern, prolonged condition of tooth growth arose late in human evolution, and that the enamel thickness of earlier hominins may not be homologous to the modern condition. This study represents the first integrated investigation of molar crown enamel thickness, volume, and development in fossil hominins, aimed at determining whether differences between AMH and living populations can be detected in these traits. Using high-resolution micro-computed tomography, we demonstrate similarities in enamel thickness and crown volumes between fossil and modern populations. Additionally, long-period growth line numbers and estimates of crown formation times for AMH molars fall within modern human ranges. These findings suggest that tooth structure and growth have remained constant for more than 60 000 years, despite the known geographical, technological, and ecological diversity that characterizes later stages of human evolution.