McKay & Dennett's (M&D's) description of beliefs, and misbeliefs in particular, is a commendable contribution to the literature; but we argue that referring to beliefs as adaptive or maladaptive can cause conceptual confusion. “Adaptive” is inconsistently defined in the article, which adds to confusion and renders it difficult to evaluate the claims, particularly the possibility of “adaptive misbelief.”

The mere fact that a particular aspect of mind could offer an adaptive advantage is not enough to show that that property was in fact shaped by that adaptive advantage. Although it is possible that the tendency towards positive illusion is an evolved misbelief, it it also possible that positive illusions could be a by-product of a broader, flawed cognitive mechanism that itself was shaped by accidents of evolutionary inertia.

I highlight and amplify three central points that McKay & Dennett (M&D) make about the origin of failures to perform biologically proper functions. I question whether even positive illusions meet criteria for evolved misbelief.

In their target article, McKay & Dennett (M&D) conclude that only “positive illusions” are adaptive misbeliefs. Relying on overly strict conceptual schisms (deficit vs. motivational, functional vs. organic, perception vs. belief), they prematurely discount delusions as biologically adaptive. In contrast to their view that “motivation” plays a psychological but not a biological function in a two-factor model of the forming and maintenance of delusions, we propose a single impairment in prediction-error–driven (i.e., motivational) learning in three stages in which delusions play a biologically adaptive role.

Inducing religious thoughts increases prosocial behavior among strangers in anonymous contexts. These effects can be explained both by behavioral priming processes as well as by reputational mechanisms. We examine whether belief in moralizing supernatural agents supplies a case for what McKay & Dennett (M&D) call evolved misbelief, concluding that they might be more persuasively seen as an example of culturally evolved misbelief.

McKay & Dennett (M&D) identify positive illusions as fulfilling the criteria for an adaptive misbelief, but could there be other types of beliefs that may qualify as adaptive misbeliefs? My commentary addresses this and other questions through identifying belief in free will as a potential candidate as an adaptive misbelief.

McKay & Dennett (M&D) convincingly argue against many proposals for adaptively functioning misbelief, but the conclusion that true beliefs are generally adaptive does not follow. Adaptive misbeliefs may be few in kind but many in number; maladaptive misbeliefs may routinely elude selective pruning; reproductively neutral misbeliefs may abound; and adaptively grounded beliefs may reliably covary with but not truthfully represent reality.

Most human beliefs are acquired through communication, and so are most misbeliefs. Just like the misbeliefs discussed by McKay & Dennett (M&D), culturally transmitted misbeliefs tend to result from limitations rather than malfunctions of the mechanisms that produce them, and few if any can be argued to be adaptations. However, the mechanisms involved, the contents, and the hypothetical adaptive value tend to be specific to the cultural case.

McKay & Dennett (M&D) suggest that some positive illusions are adaptive. But there is a bidirectional link between memory and positive illusions: Biased autobiographical memories filter incoming information, and self-enhancing information is preferentially attended and used to update memory. Extending M&D's approach, I ask if certain false memories might be adaptive, defending a broad view of the psychosocial functions of remembering.

McKay & Dennett (M&D) look for adaptive misbeliefs that result from the normal, though fallible, functioning of human cognition. Their account can be substantially improved by the addition of two elements: (1) significance of a belief's testability for its functionality, and (2) an account of reason appropriate to understanding systemic misbelief. Together, these points show why religion probably is an adaptive misbelief.

Belief in evolved belief systems stems from using a population-genetic model of evolution that misconstrues the developmental relationship between genes and behaviour, confuses notions of “adapted” and “adaptive,” and ignores the fundamental role of language in the development of human beliefs. We suggest that theories about the evolution of belief would be better grounded in a developmental model of evolution.

Nothing in McKay & Dennett's (M&D's) target article deals with the issue of how the adaptivity, or some other aspect, of beliefs might become a biological adaptation; which is to say, how the functions discussed might be coded in such a way in the brain that their development was also coded in gametes or sex transmission cells.

It is a foundational prediction of evolutionary theory that human beliefs accurately approximate reality only insofar as accurate beliefs enhance fitness. Otherwise, adaptive misbeliefs will prevail. Unlike McKay & Dennett (M&D), we think that adaptive belief systems rely heavily upon misbeliefs. However, the case for positive illusions as an example of adaptive misbelief is weak.

I argue that adaptive, self-directed misbeliefs are likely more prevalent and important than McKay & Dennett (M&D) claim. Humans often falsely interpret their own behavior in terms of culturally afforded categories. Despite their falsity, such self-interpretations are often adaptive because of our disposition to behave consistently with them. This makes us easier to interpret by similarly enculturated interactants.

The commentaries raise a host of challenging issues and reflect a broad range of views. Some commentators doubt that there is any convincing evidence for adaptive misbelief, and remain (in our view, unduly) wedded to our “default presumption” that misbelief is maladaptive. Others think that the evidence for adaptive misbelief is so obvious, and so widespread, that the label “default presumption” is disingenuous. We try to chart a careful course between these opposing perspectives.