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Morphological and biogeochemical evidence suggest that australopithecines had diets markedly different from those of extant great apes. Stable carbon isotope analysis, for example, has shown that significant amounts of the carbon consumed by australopithecines were derived from C4 photosynthesis in plants. This means that australopithecines were eating large quantities of C4 plants such as tropical grasses and sedges, or were eating animals that were themselves eating C4 plants. In contrast, there is no evidence that modern apes consume appreciable amounts of any of these foods, even in the most arid extents of their ranges where these foods are most prevalent. Environmental reconstructions of early australopithecine environments overlap with modern chimpanzee habitats. This, in conjunction with the stable isotope evidence, suggests that australopithecines and great apes, even in similar environments, would utilize available resources differently. Thus, the desire or capacity to use C4 foods may be a basal character of our lineage. We do not know, however, which of the nutritionally disparate C4 foods were utilized by hominids. Here we discuss which C4 resources were most likely consumed by australopithecines, as well as the potential nutritional, physiological, and social consequences of eating these foods.