Evolutionary Dynamics and Extensive

Noncooperative game theory is one of a handful of fundamental frameworks used for economic modeling. It is therefore troubling that the solution concepts on which the theory’s predictions are based are not as firmly grounded as one might desire. For example, while Nash equilibrium is the starting point for most game theoretic analyses, the conditions on players’ rationality and knowledge needed to ensure that a group of players will play a Nash equilibrium are disconcertingly strong. If game theoretic solution concepts can only be derived from heroic assumptions about individuals’ abilities, predictions based on these concepts are cast into doubt. Evolutionary game theory offers a novel approach for generating and justifying predictions of behavior in strategic situations. Under the evolutionary paradigm, one associates a large population of agents with each player role in the underlying game. Rather than impose strong requirements on individual agents’ abilities, one assumes instead that agents dynamically adjust their choices in response to the choices made by others. Among other things, this framework allows one to ask whether and when the empirical distributions of agents’ choices will come to resemble a Nash equilibrium of the underlying game. Evolutionary game theorists have succeeded in characterizing a range of contexts in which populations can learn to behave as the standard theory predicts. Still, from the point of view of applied research these developments leave a significant gap. The vast majority of work on evolution in games focuses on normal form games. In contrast, most economic applications of game theory are based on extensive form games. Of course, one can analyze the latter games in terms of their reduced normal forms, but evolutionary analyses based on the reduced normal form ignore the original game’s extensive form structure. This structure underlies the basic refinements of Nash equilibrium, and can also considerably simplify equilibrium computations—compare the fixed point methods required to find Nash equilibria with the backward induction techniques used to compute subgame perfect equilibria. For these reasons, the development of new techniques for studying extensive form evolution is a topic of obvious importance. Ross Cressman’s Evolutionary Dynamics for Extensive Form Games is the first book length study of evolution in games with sequential moves. Cressman shows how the