Functions of Sleep

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Functions of Sleep

  • Theories of sleep incorperate biological and psychological factors and humans spend about a thrid of their time asleep, suggesting a crucial biological function.
  • Sleep is one of the last complex behaviours which the exact purpose is still unclear.
  • Good theories tend to explain the universal nature of sleep, as it is found throughout the animal world.
  • All mammals and birds sleep, and fish, reptiles and amphibians also exhibit periods of quite restfulness that is like sleep.
  • This suggests that it must perform som critical function; although there are wide variations between humans in sleep duration, it is generally seen as necessary, with and average being 6 - 8 hours a night.
  • The best two proposed theories are the restoration and evolutionaru theory.

Evolutionary Explainations

  • Evolutionary explanations see sleep as serving some adaptive function related to survival and therefore occuring through natural selection.
  • Different species evolved different types and patterns of sleep, dealing with different environmental needs, such as, predator avoidance, conservation of energy amd dietary requirements.
  • Because of this animal species should vary in their sleep needs depending on how much they they need to search for food and how safe they are from predators when they sleep.
  • Sleep keeps animals dormant when activites vital for survival are not required.
  • Evolutionary explanations therefore see the function of sleep as similar to hibernating; conserving energy at times when they would not function efficiently, and to protect them at night when they are vunerable to predators.
  • Sleep is therefore an evolutionary stable strategy, increasing individuals and species survival.
  • Predator-prey sleep - Meddis (1979) believes that sleep evolved to keep animals hidden from predators when usual activites, like foraging, are not required.
  • Hibernation theory - Webb (1982) believes that active animals need larger amounts of food, threatening survival during times of food scarcity. Hibernation conserves energy, thus increasing survival. Grizzly bears hibernate through the winter, living off body fat accumulated during times of food availability.
  • Aquatic mammals - the precise environmental demands of species affect sleep patternsand behaviours. Aquatic mammals need to breath, so sleep incurs a risk of drowning. Animals have evolutionary strategies to cope with this problem.
  • Foraging needs - evolutionary explanations see sleep duration as affected by the amount of time needed to eat. Grazing animals spend a long time feeding, while predators sleep a lotm only needed to eat periodically.
  • Body size - smaller animals evolved a greater need to sleep, their metabolic rates being high and energy consumption rapid. Long periods of sleep helps to conserve energy stores.

Research on Evolutionary Explanations:

  • Stear (2005) - reported that sleep saves energy, keeps individuals from being lively at unneccassary times and is an adaptation to ecological factors differing across species, supporting the evolutionary basis for sleep.
  • Requadt (2006) - found that animals locate warm, safe places to sleep as it minimises energy requirements to maintain body temperature, supporting the evolutionary point of view.
  • Pilleri (1979) - found that Indus dolphins sleep for a few seconds repeatedly, supporting


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