Into the Crowd The Science of How People Behave in Numbers

Imagine you are standing in a field in England in the year 1906. It is county fair day in Plymouth, and the smell of hay and roasted meat hangs in the autumn air. A slaughtered ox has been displayed near the entrance, and someone has had the idea of running a competition. For a penny, you can write your best guess of the animal's weight on a ticket. The closest estimate wins a prize.

About eight hundred people try their luck that day. Farmers with decades of experience eyeball the carcass. Butchers make careful professional judgments. Townspeople with no expertise whatsoever scribble down wild guesses. When the statistician Francis Galton later gathered all the tickets and analyzed the data, he expected to find a mess — a chaotic scattering of numbers reflecting the ignorance of the masses. What he found instead stopped him cold. The median of all eight hundred guesses was 1,207 pounds. The actual weight of the ox was 1,198 pounds. The crowd, in aggregate, had come within less than one percent of the correct answer. No single individual had done better.

Galton published this finding with barely concealed astonishment. He had spent much of his career arguing for the superiority of gifted individuals over common populations. And here was an ox in a field in Plymouth quietly dismantling his assumptions.

This moment — this small, muddy, barnyard epiphany — sits at the entrance to one of the most contested and consequential fields in all of science: the study of collective human behavior.