The greatest mystery of the development of agriculture and organized building is why it happened so late. It appears to have begun spontaneously at distant, disconnected centers (South America and Turkey/Palestine) almost as soon as the sea level rose, suggesting it only needed the right conditions to flower.

Earlier ice ages made life in higher latitudes difficult, but the tropics were never cold. We find no hint that the developments we know of were products of earlier development--aside from the decidedly mature stone carving at Göbekli Tepe, which has no known antecedents, although they must exist somewhere.

The unique event was the Younger Dryas cold spell, with its very sharp rises in ocean level at onset and for long after. How that provoked development is a matter of conjecture, but we know that many people must have been displaced by rising water, which would have forced openness to other changes as a matter of survival.