Fixity of thinking and the foundations of identity: An argument for the evolutionary adaptiveness of delusions

Epidemiological evidence suggests that psychosis occurs along a continuum of severity in the general population. Although clinical psychotic symptoms are associated with distress and impairment, less is known about sub-threshold delusion-like experiences. The present paper conceptually explores the possibility that fixed ideas or mildly illogical thinking may be adaptive at low to moderate severity levels. Strongly held beliefs that are resistant to reality checking may facilitate identification with particular social groups. For example, tenaciously maintaining one-sided political beliefs even in the face of contrary evidence may not be fully logical, but may provide a shared sense of group identity with others who share similar beliefs. Identifying with a group provides both emotional and instrumental sources of support in the face of adversity. Maintaining illogical fixed ideas or mildly delusion-like thoughts may be evolutionarily adaptive relative to overly logical thought or, at the other end of the spectrum, clinical delusions.