ABSTRACT
Sleep helps animals to survive by keeping them out of trouble and by reducing wear and tear during their spare time. This idea is not unfamiliar to students of animal behaviour but is usually regarded as very strange by people who have thought of sleep mainly as a human activity. One of the important consequences of the immobilisation theory is that sleep may no longer be necessary in modern, civilised, opulent man. A passive surface sleep has been described during which the porpoise hangs near the surface with the head and trunk almost parallel to the water surface and the tail dangling down somewhat. Even more interesting than sleeplessness in animals, is the possibility of finding a person who does not need to sleep. It is after all quite common to read newspaper articles about people who claim not to sleep. Observations of human nonsomniacs indicate that reduced sleep need can either be inherited or acquired.
