1 .The evidence presented in this section suggests that the primary function of sleep is to permit the brain to rest. But could sleep also have some other functions? For example, could sleep serve as an adaptive response to keep animals out of harm’s way, as well as provide some cerebral repose? Sleep researcher William Dement pointed out that one of the functions of the lungs is communication. Obviously, the primary function of our lungs is to provide oxygen and rid the body of carbon dioxide, and this function explains the evolution of the respiratory system. But we can also use our lungs to vibrate our vocal cords and provide sounds used to talk, so they play a role in communication, too. Other functions of our lungs are to warm our cold hands (by breathing on them), to kindle fires by blowing on hot coals, and to blow out candles. With this perspective in mind, can you think of some other useful functions of sleep?