The normalcy of neurosis: evolutionary origins of obsessive-compulsive disorder and related behaviors.

One of the most curious questions plaguing subscribers of evolutionary theory is how natural selection's fine-tuned editing function could allow disease to persist. For evolutionary psychiatrists, the existence of psychopathology is thus perplexing. To illustrate a potential answer to one instance of this broad question, we examine the correlates of obsessive-compulsive disorder (OCD) within our normal repertoire of thought and action. The evidence presents a picture of OCD as a dysregulation of normal behaviors and mental states throughout the course of human development. We speculate that such correspondence may be more than a coincidence and that OCD is a consequence of a dysregulation of the neural circuits that are crucially involved in threat detection and harm avoidance. These neural systems are also likely to underlie aspects of religious experience and ritual as well as the wonders of romantic and early parental love.