2004 presidential address: the sheep, the ostrich, the ant, diabetes, and the tragedy of the common.

W hen I first began considering what I would like to speak about today, I reviewed the last five presidential lectures. After considering these, it didn't seem like there was much left to cover! There was, however, the irresistible urge to have, at least, a catchy title, hence " The Sheep, the Ostrich, the Ant, Diabetes , and the Tragedy of the Common. " What links these things together? In 1968, Garrett Hardin published a thought-provoking article in the journal Science describing what he called, the " tragedy of the Commons " (1). Hardin was a population biologist concerned about the issue of population growth both in the U.S. and abroad. Briefly stated, the article suggested that the problem of population growth could be likened to the dilemma that arises when a community maintains a common resource. The example that Hardin gave was that of a common grazing area. It was a frequent practice in the early years of this country, and in many areas of the world still, for villages and towns to create and maintain a common grazing area. This was land that had been cleared by the community where sheep, cattle, or other animals could graze in a shared field or " Common " that was owned, not by any individual, but by the entire community. If we visit Boston today we can still see its Common—no longer a grazing field, but still a community resource. Hardin pointed out that, in the setting of a communally shared grazing field, there is a near-irresistible temptation for each member of the community to add additional sheep or cattle to graze the common ground. This temptation can be illustrated mathematically. If there are n sheep grazing on the common meadow, each member of the community can consider the benefit and deficit of adding one additional sheep. For the community member adding another animal the benefit equals 1. The benefits to the individual are clear: he or she will have one more animal as a source of wool, milk, or meat for his family. What about the deficits or costs? These are less clear. However, with some thought, the farmer realizes that the ability of the common grazing ground to support a flock of sheep is not without limit. Vegetation, water, or other resources may be exhausted. Upon further reflection, he also realizes that the burden of overpopulation is shared among …