[Phylogeny of sleep stages].

The states of sleep in man (orthodox and paradoxical sleep) are the achievement of a long evolution which has successively integrated several mechanisms. The circadian clock (predictive homeostasis) a system responsible for saving energy utilisation, a mechanism which adapts the duration of sleep to the preceding duration of waking (reactive homeostasis) and finally the apparition of an ultradian pace maker in homeothermic mammals which will be responsible for dreaming in man.