The Population Bomb, published by Stanford biologist Paul Ehrlich in 1968, predicted that populations would grow more quickly than food supplies, causing mass starvation. Ehrlich was wrong: food supplies kept pace. And that’s largely due to the years Norman Borlaug spent growing different strains of wheat in Mexico. The 'green revolution' vastly increased yields of wheat, corn and rice. Yet, as Tim Harford describes, worries about overpopulation continue. The world’s population is still growing, and food yields are now increasing more slowly – partly due to environmental problems the green revolution itself made worse. Will new technologies come to the rescue?