This chapter presents major advantages (a triune model) that sleeping on the ground may have provided which outweighed the dangers. It covers some other theorists' speculations as to the reasons we sleep and dream. The chapter proposes that sleep, including slow-wave, rapid eye movements (REM), and dreaming may have evolved for at least three overlapping, non-mutually exclusive reasons: recuperative, adaptive, and mnemonitive. Hobson and McCarley proposed a neurophysiological explanation for REM sleep. They called their model an activation-synthesis hypothesis which proposed that dreams do indeed represent an active model of the brain during sleep; however, this activation is not necessarily evolutionarily advantageous; in fact, they said, dreams are essentially meaningless and random. Winson has established that a theta rhythm of 6 Hz arises from the hippocampus of awake animals in specific and important functions, such as exploratory behavior in rats, a fear response resulting in rigidity in rabbits, and predation in cats.