A commons is, in its most simplistic form, a finite resource shared by a group. The idea of the Tragedy of the Commons, is that members of a group tend to overuse a shared resource when there are no cultural mechanisms to mete out access.

This article in Science magazine shows how a previous existing commons with reasonably adequate controls of use of a shared resource can quickly breakdown when “anti-commons” practices are introduced.

In this case, previously medical research into the human genome was an open commons. No one could really own the shared resource that was the genome. In recent years, companies have found ways to patent portions of the genome. This not only has the obvious immediate effects of stifling research but has deeper impacts as well.