In 1907, Sir Francis Galton asked 787 villagers to guess the weight of an ox. None of them got the right answer, but when Galton averaged their guesses, he arrived at a near perfect estimate. This is a classic demonstration of the “wisdom of the crowds”, where groups of people pool their abilities to show collective intelligence. Galton’s story has been told and re-told, with endless variations on the theme. If you don’t have an ox handy, you can try it yourself with beans in a jar.
To Iain Couzin from Princeton University, these stories are a little boring. Everyone is trying to solve a problem, and they do it more accurately together than alone. Whoop-de-doo. By contrast, Couzin has found an example of a more exciting type of collective intelligence—where a group solves a problem that none of its members are even aware of. Simply by moving together, the group gains new abilities that its members lack as individuals.
Couzin–one of National Geographic’s Emerging Explorers–has spent his whole career studying animals that move in shoals, flocks and swarms. His early work involved ants and locusts but when he started his own lab at Princeton, he thought he’d upgrade to a smarter group-living species. Unfortunately, he ended up with the golden shiner—a small, bland, minnow-like fish that’s dumb beyond the telling of it.
Consider this: shiners have a natural preference for darkness. Plop a shoal of them into a pool of water, and they’ll head for the shadiest bits. This is something that animals do all the time: They track gradients in their environment. A migrating robin might follow the Earth’s magnetic field, a moth might follow the scent of a flower, or an ant might track the pheromones laid by its nest-mates. But single shiners are laughably bad at this.
Andrew Berdahl and Colin Torney from Couzin’s team discovered their ineptitude by projecting shifting patterns of light over a shallow pool and adding the shiners in increasing numbers. Overhead cameras tracked their movements, and the team calculated how good they were at chasing the shadows.
The solo fish did so badly that they were almost swimming randomly. Only larger shoals were good at avoiding the shifting light. Even then, Berdahl and Torney found that the shiners’ movements were far more influenced by what their neighbours were doing, than by how bright the environment was.
That’s the key. The individual fish aren’t tracking anything. That would involve realising, for example, that it’s getting darker over there compared to over here, and swimming over there. Instead, they obey one very simple rule—swim slower when it’s dark. Each fish just reacts to how bright it is in its current position. How bright or dark is it right here? That’s a scalar measurement. It’s the shoal that converts these local readings into a vector.