The centuries between 800 and 300 BC sae an explosion of new religious and philosophical concepts. Their emergence is second only to man's harnessing of fire in fundamentally transforming our understanding of what is to be human. But why did Socrates, Buddha, Confucius, Jeremaiah and Lao Tzu - among others - all emerge in this 500-year span? And why did they have such similar ideas about humanity?