For most of our history, the human population grew slowly. Until new discoveries brought us more food and made us live longer. In just a hundred years the human population quadrupled. This led to apocalyptic visions of an overcrowded earth. But the population growth rate actually peaked in the 1960s. Since then, fertility rates have crashed as countries industrialize and develop. World population is now expected to balance out at around 11 billion by the end of the century. But the big picture conceals the details.