 It is proposed that REM sleep evolved from short bouts of motor activity in reptiles while Slow-Wave Sleep (SWS) evolved from their basking state which shows similar slow wave EEG patterns.Reptiles have quiescent periods similar to mammalian sleep, and a decrease in electrical activity in the brain has been registered when the animals have been asleep.However, the EEG pattern in reptilian sleep differs from what is seen in mammals and other animals.