MathBench > Environmental Science

Tragedy of the Commons

Portrait of a tragedy

Usually we think of common rights as a good thing, so why is common benefit such a problem?


goatHereís what happensÖ As a villager, I have a right (like everyone else) to let my goat graze on the village land. But the goat itself doesnít belong to the village. The goat belongs to me. Iím the one that is making goat cheese, and when I have enough cheese, I plan to slaughter it (the goat, not the cheese!) and roast it over a fire. So that means my goat is eating for free from the village lands, and Iím personally getting the benefit of goat products.

So, being a forward thinking villager, I realize that this is a pretty good deal. In fact, why stop with just one? I could get twice the benefit by raising 2 goats. Remember, I donít have to pay for them to eat, so once Iíve paid for the second one, its pure profit for me.

But of course the rest of the villagers are just as smart as I am. They all realize that double your goat = double your fun. As long as the village has plenty of grazing land, this is fine for everyone.

many goatsIn fact, several of us decide that 3 goats are better than 2. Now in fact the grazing land is getting a little crowded. Each goat that gets added degrades the land just a little. The soil gets slightly more compacted. The grass get bare in a couple more places. Goat poop starts to build up.

Does this slight degradation cause me, as an individual villager, to decide not to get another goat? Probably not. Remember, the land is getting a little worse because of my one extra goat, but I get the benefit of the entire goat!! Even if that goat gives slightly less milk, and grows slightly smaller, its still basically eating for free, so what the heck?

In fact, it is in my interest (and everyone elseís interest) to keep adding goats as long as they can graze enough to make even a slight profit.