PSYA3 Evo

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  • Evolutionary Explanations of Sleep
    • A01
      • Suggests human and non-human animals have all evolved to sleep because of their survival values.
      • A reason why we sleep is energy conservation because warm blooded mammals spend a lot of time and energy trying to maintain their body temperature. Animals with high metabolic rates have more of a problem than animals with low rates because they use more energy.
        • Thus, sleep provides a purpose of inactivity, which is similar to hibernation (a way of saving energy).
      • The theory sees sleep duration being affected by the amount of time needed to eat. Stock-grazing animals spend a long time feeding while predators sleep a lot.
        • For example, cows + horses eat grass with low nutritious value and cannot afford to spend long amounts of time sleeping whereas, carnivals eat high nutritious foods so can therefore spend long time resting.
      • Sleep is constrained by predation risks. A predator can sleep for longer as they don't have to worry about being hunted/ Prey has to stay awake and vigilant so they are prepared if they are attacked.
      • Sleep patterns may have evolved into an ecological niche,this is the environment the animal inhibits and their lifestyle which may be the because for unilateral sleep. Unilateral sleep is when one hemisphere of the brain is asleep whilst the other is awake.
    • A02
      • Webb believed that active animals need larger amounts of food, hibernation conserves energy therefore increasing survival
      • Research has been done on the costs and benefits of sleep between species by Zepelin + Rechtschaffen
        • They found that smaller animals with high metabolic rates sleep more than larger animals.This supports the energy conservation view that it might be the only or main reason for sleep.
      • Alison + Cicchetti provided supports for predator avoidance.
        • They examined sleep patterns in 39 animals finding that prey animals slept a lot less than predators. This suggests that Meddis' study of prey/predator sleep theory is flawed.
          • However, Lesku pointed out that prey animals are usually herbivorous so needing longer periods awake to consume food.
      • Unilateral sleep has evolved in aquatic marine animals as animals like dolphins need this to take breaks so they don't drowned. Mukhametov found that bottlenose dolphins have one cerebral hemisphere at a time, allowing animals to sleep + breath at the same time.
      • The evolutionary approach fails to address why we have such a strong drive to sleep. Horne proposed a theory that combines elements from both views and there is a distinct distinction between core and optional sleep.
        • Core skeep is stage 4 and REM sleep which is vital and optional is stages 2 & 3 which is not important but it can be the use of unproductive hours.
      • A lot of research involving evolutionary explanations depend on animal studies providing a problem when generalising the findings to humans.

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