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A study on the teeth of ancestors to humans that lived around 3.5 million years ago has found they were mostly or totally vegetarian. The consumption of animal foods such as meat is considered to be a crucial turning point in human evolution, that archaeologists link to the growth of the brain and the ability of pre-humans to make and use tools. But evidence of when prehistoric people started eating meat has been difficult to find. Australopithecus was a hominin—a human-like mammal—that walked on two legs but had smaller brains than Neanderthals and modern humans. In this study, scientists at the Max Planck Institute for Chemistry in Germany and the University of Witswatersrand (Wits) in South Africa analyzed different versions of nitrogen present in the fossilized tooth enamel of seven Australopithecus individuals found in southern Africa. Analyzing nitrogen isotopes—different forms of nitrogen that might be heavier or lighter depending on the neutrons i...