Stable isotopes serving as a checkpoint

Abstract

Modern African great apes, even the so-called “savanna chimpanzees,” have relatively restricted diets consisting largely of leaves and fruits from C3 plants (1). In contrast, fossil members of the genus Homo, like their modern descendants, are believed to have had a rather eclectic diet, consuming foods from C3, C4, and crassulacean acid metabolism plants, while also complementing their diet with calorie-rich animal foods (2). Deeper in the fossil record, stable carbon isotope data suggest that at 4.4 Ma, the putative early hominin taxon Ardipithecus had a diet similar to modern chimpanzees, mostly consuming resources derived from C3 plants (3). Thus, the timing of significant C4 inclusion in the hominin diet following evolutionary divergence from the great apes at ca. 6–7 Ma is critical, because the event represents a milestone in human evolution that may relate to major shifts in early hominin habitat, ecology, and even physiology. In PNAS, Levin et al. (4) contribute to a better understanding of these issues in early hominins.