Domination of cooperation without and with wealth accumulation.

The contour plot shows the percentage of runs that end with more than 99% cooperators, as a function of the payoff parameters (horizontal axis) and (vertical axis). In a world in which wealth is not accumulated (A), the range of parameters for which cooperation can take over is very limited (blue area in A). When the rich get richer (B), however, the range of parameters is far larger (blue area in B).