ABSTRACT
An understanding of the nature, amount, and distribution of rapid eye movement (REM) sleep across the animal kingdom allows one to form hypotheses about its evolutionary history and function. Most studies of sleep have been conducted in humans, with lesser numbers in “standard” laboratory animals such as the rat, rabbit, and dog. However, those studies that have been undertaken clearly show that REM sleep amounts vary enormously across the animal kingdom. The behavioral similarity of the REM sleep state in the human and cat makes it reasonable to hypothesize that the neuronal activity changes known to underlie the state of REM sleep in the cat are occurring in the human. The ubiquity of REM sleep in mammals and its presence in birds are most parsimoniously explained if one hypothesizes a single origin of this state in the common reptilian ancestors of birds and mammals.
