Only once we understand the long history of human efforts to draw sustenance from the land can we grasp the nature of the crisis that faces humankind today, as hundreds of millions of people are faced with famine or flight from the land. From Neolithic times through the earliest civilizations of the ancient Near East, in savannahs, river valleys and the terraces created by the Incas in the Andean mountains, an increasing range of agricultural techniques have developed in response to very...