One of the fundamental questions of our existence is why we are so smart. There are lots of drawbacks to having a large brain, including the huge food intake needed to keep the organ running, the frequency with which it goes wrong, and our very high infant and mother mortality rates compared with other mammals, due to the difficulty of giving birth to offspring with very large heads. So why did evolution favour the brainy ape? This question has been widely debated among biological anthropologists, and in recent years, Maslin and his colleagues have pioneered a new theory that might just be...

What drove the evolution of humans, with our uniquely big brains? The Cradle of Humanity presents fascinating and controversial new research which suggests that the geological and climatic history of East Africa's Rift Valley are at the heart of the answer.