Rethinking Rationality: From Bleak Implications to Darwinian Modules

There is a venerable philosophical tradition that views human beings as intrinsically rational. But studies have shown that even under ordinary circumstances where fatigue, drugs, and strong emotions are not factors, people reason and make judgments in ways that systematically violate familiar canons of rationality on a wide array of problems. These studies sparked the growth of a major research tradition whose impact has been felt in economics, political theory, medicine, and other areas far removed from cognitive science. This chapter is organized as follows. Section 2 sketches a few of the better-known experimental findings. Though there is little doubt that most of the experimental results reported in the literature are robust and can be readily replicated, there is considerable debate over what these experiments indicate about the intrinsic rationality of ordinary people. One widely discussed interpretation of the results claims that they have "bleak implications" for the rationality of the man and woman in the street. Section 3 elaborates on this interpretation and explains the technical notion of competence that it invokes. Section 4 offers a detailed sketch of the richly modular picture of the mind advanced by evolutionary psychologists and of the notion of a mental module that plays a fundamental role in that picture. Section 5 considers several recent studies that appear to confirm the evolutionary psychologists' prediction: When information is presented in ways that would have been important in our evolutionary history, performance on reasoning tasks soars. The final section asks a hypothetical question: If the evolutionary psychologists' account turns out to be on the right track, what implications would this have for questions about the nature and the extent of human rationality or irrationality?.