Toward an Evolutionary Theory of Dreaming

The basic mystery of the biological condition associated with human dreaming, the REM State, is how the purposes of survival are served by such intervals of remarkable nervous excitation which punctuate the sleep of all mammals. The author postulates that while extended sleep achieves conservation of energy, the REM State serves a "sentinel" function, bringing about brief but periodic awakenings after preparing the organism for immediate fight or flight. Such a built-in physiological mechanism presumably would provide maximal security from external danger compatible with minimal disturbance to the continuity of sleep. These may have been unique and critical survival advantages in the early mammalian predicament.