20 percent defectors (free riders), and 63 percent reciprocators in this particular experiment. “Our results support the view that our human subject population is in a stable … equilibrium of types,” wrote the researchers, Robert Kurzban and Daniel Houser.22 Knowing about the Nash equilibrium helps make sense of results like these.

GAME THEORY TODAY

Together with his paper on the bargaining problem (which treats cooperative game situations), Nash’s work on equilibria in many-player games greatly expanded game theory’s scope beyond von Neumann and Morgenstern’s book, providing the foundation for much of the work in game theory going on today. There’s more to game theory than the Nash equilibrium, of course, but it is still at the heart of current endeavors to apply game theory to society broadly.

Over the years, game theorists have developed math for games where coalitions do form, where information is incomplete, where players are less than perfectly rational. Models of all of these situations, plus many others, can be built using game theory’s complex mathematical tools. It would take a whole book (actually, several books) to describe all of those subsequent developments (and many such books have been written). It’s not necessary to know all those details of game theory history, but it is important to know that game theory does have a rich and complex history. It is a deep and complicated subject, full of many highly technical and nuanced contributions of substantial mathematical sophistication.

Even today game theory remains very much a work in progress. Many deep questions about it do not seem to have been given compelling answers. In fact, if you peruse the various accounts of game theory, you are likely to come away confused. Its practitioners do not all agree on how to interpret some aspects of game theory, and they certainly disagree about how to advertise it.

Some presentations seem to suggest that game theory should predict human behavior—what choices people will make in games



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