Picture a flock of birds gathering around a feeder that no one built. Each bird searches for food on its own, yet they all end up together. Usually, such behavior is explained by social instinct: birds want to be near their kin. But what if the flock is simply a side effect of greed?

The agents lived on a square arena with sides of 50 steps. Scattered around were 100 "feeders"—targets that, once captured, disappeared for a while. Each agent could see only what lay ahead, within a narrow cone of vision. It could tell whether a conspecific was there and whether that individual had recently visited a feeder. There was no reward for being near others—only for food.

With a small visual radius, the agents behaved like loners: they wandered across the arena, occasionally bumping into targets. But when the visual radius was increased, a sharp jump occurred: the agents began to spin in place until they spotted a "satiated" conspecific, then ran straight toward it. At that moment, they clumped together.

This transition can be explained by a simple model. The solitary strategy is blind search, like a person looking for keys in the dark. The collective strategy is running toward someone who has already found the prize. When the visual radius is small, it pays to search on your own. When it is large, it pays to watch others. Somewhere in between lies the point where the benefits balance out.

So a flock can arise from pure greed. Agents do not need to want to be together—they simply need to want to eat. And this finding changes how we view collective behavior: perhaps birds and fish school not because they enjoy company, but because it is the best way to find dinner.