Two little-known twentieth-century scientists, Norman Borlaug and William Vogt, whose diametrically opposed views shaped our ideas about the environment, laying the groundwork for how people in the twenty-first century will choose to live in tomorrow's world. In forty years, Earth's population will reach ten billion. Can our world support that? What kind of world will it be? Those answering these questions generally fall into two deeply divided groups - Wizards and Prophets, as Charles Mann calls them. The Prophets, he explains, follow William Vogt, a founding environmentalist who believed that in using more than our planet has to give, our prosperity will lead us to ruin. Cut back! was his mantra. The Wizards are the heirs of Norman Borlaug, whose research, in effect, wrangled the world in service to our species to produce modern high-yield crops that then saved millions from starvation. Innovate! was Borlaug's cry. Science journalist Charles Mann delves into these diverging viewpoints to assess the four great challenges humanity faces - food, water, energy, climate change - grounding each in historical context and weighing the options for the future. With our civilization on the line, this is an essential addition to the urgent conversation about how our children will fare on an increasingly crowded Earth.