Our brains are huge, particularly if you take into consideration the relative size of our bodies. Generally, the proportion of brain to body is pretty tight among mammals. But the human brain is seven times bigger than what you’d predict from the size of our body. Six million years ago, hominid brains were about a third the size they are today, comparable to a chimp’s. So what accounts for the big boom? It would be flattering ourselves to say that the cause was something we are proud of–our ability to talk, or our gifts with tools. Certainly, our brains show signs of being adapted for these sorts of things (consider the language gene FOXP2). But those adaptations probably were little