Deeply Rational Reasons for Irrational Beliefs

Why do people hold irrational beliefs? Two accounts predominate. The first spotlights the information ecosystem and how people process this information; this account either casts those who hold irrational beliefs as cognitively deficient or focuses on the reasoning and decision-making heuristics all people use. The second account spotlights an inwardly-oriented and proximate motivation people have to enhance how they think and feel about themselves. Here, we advance a complementary, outwardly-oriented, and more ultimate account—that people often hold irrational beliefs for evolutionarily rational reasons. Under this view, irrational beliefs may serve as rare and valued information with which to rise in prestige, as signals of group commitment and loyalty tests, as ammunition with which to derogate rivals in the eyes of third-parties, or as outrages with which to mobilize the group toward shared goals. Thus, although many beliefs may be epistemically irrational, they may also be evolutionarily rational from the perspective of the functions they are adapted to serve. We discuss the implications of this view for puzzling theoretical phenomena and for changing problematic irrational beliefs.