National Science Foundation, The Tragedy of the Commons

The Tragedy of the Commons is a dilemma that develops when a group shares a limited resource. Imagine some farmers are sharing a pasture for their cows. The cows eat the grass, but the grass grows back and so the cows have plenty to eat. So they add more cows, which eat more grass. Eventually, the grass can barely grow fast enough to keep the cows fed. Farmer Alex decides to add another cow anyway. He figures the extra cow doesn't eat that much grass and will only mean a little less for everyone's cows, but he will get all the milk from the extra cow. “Don't look at me! if I don't, they will.” The other farmers feel the same way: each knows that they are hurting the pasture they share, but their fear of losing out seems to force their hands. That's the Tragedy of the Commons, and it doesn't just threaten cartoon pastures.

Stocks of Atlantic cod and bluefin tuna are greatly diminished. Aquifers that can replenish if water is withdrawn slowly are now emptying. Even roads can screech to a standstill while drivers wonder why others don't take public transit. By studying the interactions between people and their environments, researchers are becoming better able to figure out ways to protect ranges, forests, oceans, and even highways. This will become more and more important as the population of the earth grows but the space available stays the same. More people will be using the commons, and we may be on the brink of tragedy.