Looking at the past from this perspective makes one thing clear: somewhere within a thousand years of the first cities emerging, human beings invented a whole new way of inventing. A strong correlation exists between those dense settlements and the dramatic surge in the societal innovation rate. But is there a causal relationship between the two? The chart alone cannot tell us, and we do not know enough about the specific histories of these innovations to document how essential the urban context was to their creation. But the circumstantial evidence is strong.
