Below I paste in the abstract (and here is the PDF) of a forthcoming article in Brain and Behavioral Science by McKay and Dennett that examines possible evolutionary rationales for mistaken beliefs, bizarre delusions, instances of self-deception, etc. Of the range of potential candidates for evolved misbelief, they conclude that, among those surveyed, only positive illusions meet their criteria.
From an evolutionary standpoint, a default presumption is that true beliefs are adaptive and misbeliefs maladaptive. But if humans are biologically engineered to appraise the world accurately and to form true beliefs, how are we to explain the routine exceptions to this rule? How can we account for mistaken beliefs, bizarre delusions and instances of self-deception? We explore this question in some detail. We begin by articulating a distinction between two general types of misbelief: those resulting from a breakdown in the normal functioning of the belief formation system (e.g. delusions) and those arising in the normal course of that systems operations (e.g. beliefs based on incomplete or inaccurate information). The former are instances of biological dysfunction or pathology, reflecting culpable limitations of evolutionary design. Although the latter category includes undesirable (but tolerable) by-products of forgivably limited design, our quarry is a contentious subclass of this category: misbeliefs best conceived as design features. Such misbeliefs, unlike occasional lucky falsehoods, would have been systematically adaptive in the evolutionary past. Such misbeliefs, furthermore, would not be reducible to judicious but doxastically noncommittal - action policies. Finally, such misbeliefs would have been adaptive in themselves, constituting more than mere by-products of adaptively biased misbelief-producing systems. We explore a range of potential candidates for evolved misbelief, and conclude that, of those surveyed, only positive illusions meet our criteria.