Eureka?

An evolutionary leap? Probably not. Chimpanzees - our closest relatives who split from a common ancestor 13 million years ago - were gifted with a stable West-Central African forest environment that met all their needs. But in East Africa, our own ancestors had to cope with a drying trend that turned forest into savannah. Faced with more hunger and danger, they had to grow their minds in order to live. Chimps have all the brains they need, with no big crises driving them to get "bigger heads".