For most of history, our numbers have been negligible. If Odysseus really did sail the wine-dark sea in the 12th century B.C., he was one of only around 50 million people alive at the time. As Muhammad composed the Quran some 1,800 years later, the population was roughly 200 million. But the Industrial Revolution pushed that crawl into a sustained sprint. Our numbers doubled in just 150 years, and Malthus’ world was making room for its 1 billionth member by 1804. How would they eat? What would they drink? Where would they live?