Seven Australopithecus specimens uncovered at the Sterkfontein fossil site in South Africa were herbivorous hominins who did not eat substantial amounts of meat, according to a new study by Tina Lüdecke and colleagues. Lüdecke et al. analyzed organic nitrogen and carbonate carbon isotopes extracted from tooth enamel in the fossil specimens to determine the hominin diets. Some researchers have hypothesized that the incorporation of animal-based foods in early hominin diets led to increased brain size, smaller gut size, and increased stature – all key events in human evolution. Cut and scraped bones and some stone tools from the same time period (around 3.7 million years ago) offer hints that australopithecines were eating some meat, but there has been a lack of direct evidence for an animal diet. The researchers analyzed enamel nitrogen isotope measurements from 43 animal fossils, including the australopithecines, and modern African mammals to characterize these isotopes in known carnivores and herbivores. They found a clear separation in the enamel isotopes between the two groups, with the Australopithecus enamel significantly similar to that of the herbivore group. It’s possible, the researchers note, that the australopithecines were eating energy-rich foods with low nitrogen isotope ratios, like legumes or possibly termites. But it’s unlikely that they were eating enough meat to drive changes in brain size and other characteristics that are hallmarks of human evolution, Lüdecke et al. conclude.

A segment of Science's weekly podcast with Tina Lüdecke, related to this research, will be available on the Science.org podcast landing page [http://www.science.org/podcasts] after the embargo lifts. Reporters are free to make use of the segments for broadcast purposes and/or quote from them – with appropriate attribution (i.e., cite "Science podcast"). Please note that the file itself should not be posted to any other Web site.