ABSTRACT
Scientists who study animal behaviour have long been familiar with the idea that sleep is a very useful aspect of behaviour which favours the survival of many species in a way which has nothing to do with the repair of the hurt mind or tired body. Mammals show a great deal of variation across species in terms of the amount of sleep they take. Some sleep hardly at all and some sleep nearly all of the time. The interpretation of the results of sleep-deprivation experiments are a special example of how people's customary modes of thinking make it difficult for them to treat sleep research data objectively. After many careful experiments people can now be sure that the main effect of sleep loss is to make them very, very sleepy. The discovery of dreaming sleep proved a stimulant for sleep research in that more scientists were attracted to the field by this novelty.
