Big Brains and Small Teeth: a primate comparative approach to dental and mandibular reduction in hominins
Within the genus Homo, we observe a decrease in mandibular robusticity and in the size of anterior and postcanine dentition, a trend that is usually referred to as reduction or gracilisation. Factors linked to diet, food processing and encephalization have been suggested to be the main drivers of this trend. Stone tools and fire would have allowed Pleistocene hominins to reduce food toughness, thus relaxing the selective pressures on the masticatory apparatus. In the Holocene, the changes in human lifestyle triggered by agriculture would have determined the reduction in human tooth size. Brain expansion may have acted as a constraint on the development of the lower jaw. In this work, a primate perspective was adopted to clarify the relative influence of adaptive and non-adaptive factors on mandibular and dental reduction in the genus Homo. The effect of diet and structural constraints (allometry and encephalization) on dental and mandibular size and robusticity were analysed. The results show that incisor size and mandibular robusticity correlate significantly with diet proxies in non-human extant catarrhines and with neurocranium shape changes in the neurocranium in Homo sapiens. In non-human African apes, the elongation of the neurocranium influences postcanine tooth size. In Homo, body size plays an important part in tooth size allometry, but not in robusticity. These results suggest that improvements in tool-based food preparation may have been a leading factor in the reduction of incisor size in hominins. Molars and premolars were probably influenced by the expansion of the neurocranium during Pleistocene, and incisor size may be constrained by neurocranium shape changes in H. sapiens. This work confirmed the importance of food processing in the trend of reduction and produced convincing evidence for the significance of structural constraints in the evolution of the hominin anatomy. These findings contribute to explain the complex evolution of the human skull.
GN Anthropology, QM Human anatomy, QP Physiology, RK Dentistry
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