"The Cooperative Trap"
Braess's paradox — where adding capacity to a network increases travel time — typically assumes selfish agents. Each individual optimizes for itself, creating congestion that hurts the collective. The standard explanation: if everyone weren't so selfish, the paradox wouldn't arise.
Das Bairagya and colleagues find the paradox in Diacamma indicum ants, one of the most cooperative social systems in nature. Tandem-running ants, where a leader guides a follower along a route, preferentially choose the shortest path. This seems optimal. It isn't. The shortest path, when enough ants use it, creates congestion that slows the colony more than a longer path would. The paradox emerges not from selfishness but from a heuristic — "choose the shortest path" — that natural selection favored for good reasons but that fails at the collective level.
The quantitative model shows how evolutionary forces selecting for shortest-path identification can force suboptimal global states. The ants are cooperating. They're trying to help the colony. But the rule they're following — a rule that evolved because shorter paths are usually faster — doesn't account for the system-level effect of every leader following the same rule.
This is a deeper version of the paradox than the traffic analogy. In traffic, you can invoke individual rationality as the villain and propose tolls or coordination mechanisms as the solution. In ants, the agents are already coordinated. They already prioritize collective benefit. The trap isn't selfishness — it's a local heuristic that evolution optimized and that scales poorly. Cooperation doesn't prevent Braess's paradox. The paradox is compatible with cooperation. It's a property of the network and the heuristic, not of the agents' intentions.
