A varied diet
3.5-1.8 million years ago
Our oldest ape-like ancestors mostly ate fruit, but later species like Australopithecus branched out. As well as eating a wider range of plants, such as grasses, they seem to have eaten a lot more meat, and even butchered it with stone tools. More meat meant more calories, and less time spent chewing.
See other: What Makes Humans Human?