Increased Dietary Breadth in Early Hominin Evolution: Revisiting Arguments and Evidence with a Focus on Biogeochemical Contributions

Abstract

Increases in dietary breadth have been associated with hominin origins and the development of the genus Homo. For the former, researchers such as Dart noted that the environments associated with australopiths were not conducive for frugivorous diets like those of our closest living relatives the chimpanzees. Thus, many early arguments for increased dietary breadth were largely driven by perceived environmental constraints on diet. In contrast, the arguments for increased dietary breadth in early Homo have focused on explicating its high degree of encephalization. Biogeochemical evidence supports these ideas to varying extents. Trace element data have been used to argue for the increased utilization of animal foods among australopiths. We argue, however, that these data are equivocal and may be more consistent with the consumption of plant foods such as underground storage organs and grass seeds. Carbon isotope analysis demonstrates that australopith diets were characterized by great variability, and a tendency to consume C4 resources such as grasses, sedges, and/or animals eating these foods. This contrasts with what has been observed in chimpanzees, which exhibit little variability and do not appear to consume significant quantities of C4 resources even when such resources are locally abundant. Biogeochemistry has revealed little about the diets of early Homo, although there are data suggesting that it consumed some C4 resources, possibly in the form of underground storage organs. At present, our best evidence for increases in dietary breadth in early Homo comes from the archaeological record and physiologically based models for encephalization. We surmise that increased meat consumption among early Homo was not in and of itself responsible for a leap in dietary quality, but rather that it served as a dietary release allowing consumption of more abundant energy-rich foods with protein of lower biological value.