The Phasing of Sleep in Animals

Abstract

The tale of the hare and the tortoise typifies a fundamental enigma in the study of sleep: how can it be that animals, which we would like to think behave rationally (even if not consciously), can deny themselves clear rewards for the vaguely understood and often excessively delayed benefits of sleep? This is a particularly unpalatable proposition for animals that interrupt unfinished activities for sleep. It seems to us humans that animals should complete their day’s activities, then find a secure sleeping location and sleep well, yet such a pattern is rare in nature. Less than 14% of mammalian genera, for example, can be considered strictly monophasic (Campbell and Tobler, 1984). To explain the variety of the phasing of sleep is to confront both the reasons for sleep and the principles behind the scheduling of behavior. In this chapter several different perspectives will be used to evaluate the biological significance of the phasing of sleep in animals.