The reinterpretation of dreams: An evolutionary hypothesis of the functionof dreaming

Several theories claim that dreaming is a random by-product of REM sleep ph ysiology and that it does not serve any, natural function. Phenomenal dream content, however, is not as disorganized as such dews imply. The form and content of dreams is not random but organized and selective: during dreamin g, the brain constructs a complex model of the world in which certain types of elements, when compared to waking life, are underrepresented whereas ot hers are over represented. Furthermore, dream content is consistently and p owerfully modulated by certain types of waking experiences. On the basis of this evidence, I put forward the hypothesis that the biological function o f dreaming is to simulate threatening events, and to rehearse threat percep tion and threat avoidance. To evaluate this hypothesis, we need to consider the original evolutionary context of dreaming and the possible traces it h as left in the dream content of the present human population. In the ancest ral environment human life was short and full of threats. Any behavioral ad vantage in dealing with highly dangerous events would have increased the pr obability of reproductive success. A dream-production mechanism that tends to select threatening waking events and simulate them over and over again i n various combinations would have been valuable for the development and mai ntenance of threat-avoidance skills. Empirical evidence from normative drea m content, children's dreams, recurrent dreams, nightmares, post traumatic dreams, and the dreams of hunter-gatherers indicates that our dream-product ion mechanisms are in fact specialized in the simulation of threatening eve nts, and thus provides support to the threat simulation hypothesis of the f unction of dreaming.