Briefly describe the purpose of sleep in terms of survival theory.
The purpose of sleep in terms of the survival theory proposes that sleep evolved to enhance survival, by protecting an organism by making it inactive during part of the day when it is most risky or dangerous to move about. For example, once an organism has fulfilled all its survival functions such as eating, drinking, caring for its young and reproducing, it must spend the rest of its time conserving energy, hidden and protected from predators. While sleeping, an organism is not physically interacting with the environment and is less likely to attract the attention of potential predators. Thus, according to the survival theory, sleep serves the function of protecting the sleeper from harm or death, and therefore enhances survival of the species.