The preceding five chapters do not attempt to present a full theory of the evolution of the social contract. Rather, they are an introduction to some of the elements of such a theory. From one perspective, the elements may be seen as a list of simple models of general problem areas: bargaining games and distributive justice, ultimatum games and commitment, prisoner's dilemma and mutual aid, hawk–dove and the origin of ownership, and signaling games and the evolution of meaning.

But from another point of view, the elements of the theory are the basic conceptual tools that have been introduced along the way. In the first chapter, we met the basic concepts of Nash equilibrium and Evolutionarily stable strategy, and the replicator dynamics that stands behind the concept of evolutionary equilibrium. We saw how one could explore the effect of various factors on the size of basins of attraction of equilibrium states of the population. In Chapter 2, we saw the tension possible between commitment and modular rationality. Here the theory of rational choice and the theory of evolution begin to diverge. When we apply the replicator dynamics to the symmetrized ultimatum game, we find it does not eliminate strategies which fail the test of modular rationality. This remains true even when we introduce the “trembling hand” into our evolutionary models by adding mutation and recombination to the replicator dynamics. In Chapters 3 and 4, we met two rather different kinds of correlated equilibria.