 Darwinian dynamics thus offers qualified good news for cooperation. Notice, however, that this holds only so long as individuals are stuck with their natural or cultural programming and can’t re-evaluate their utilities for themselves. If our agents get too smart and flexible, they may notice that they’re in PDs and would each be best off defecting. In that case, they’ll eventually drive themselves to extinction—unless they develop stable, and effective, moral norms that work to reinforce cooperation. But, of course, these are just what we would expect to evolve in populations of animals whose average fitness levels are closely linked to their capacities for successful social cooperation. Even given this, these populations will go extinct unless they care about future generations for some reason. But there’s no non-sentimental reason that doesn’t already presuppose altruistic morality as to why agents should care about future generations if each new generation wholly replaces the preceding one at each change of cohorts. For this reason, economists use ‘overlapping generations’ models when modeling intertemporal distribution games. Individuals in generation 1 who will last until generation 5 save resources for the generation 3 individuals with whom they’ll want to cooperate; and by generation 3 the new individuals care about generation 6; and so on.