 This area of inquiry remains largely speculative, since it is one thing to develop models for how psychological altruism could in principle evolve, and quite another to show convincingly that a given form of natural selection has in fact played the relevant role in actual human evolutionary history. There may be doubts, for example, whether there was sufficient pair-wise engagement in iterated prisoner’s dilemma games to explain the evolution of reciprocal altruism according to some of the most familiar game-theoretic models (Kitcher 2006a,b). In any case, it is time to return to the issue of moral judgment, which is crucial to the explanation of morality proper, and goes beyond mere altruistic feeling and behavior. The following sub-section describes one leading hypothesis.