Functions of sleep- evolutionary explanation

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  • Functions of sleep- evolutionary explanation
    • Lesku et al
      • looked at the complexity accounts for the range of sleep patterns in the animal world
      • anomalies
        • sloth is a relatively large animal but sleeps for 20 hours a day
      • correlational studies
        • cannot establish cause and effect
      • difficult to distinguish between correlations and IV's
        • herbivores have to graze many hours a day so have less time to sleep
        • however, they're also prey animals and so want to diminish risk to predators
        • difficult to establish which factor is more important
      • Factors according to the evolutionary ecological approach
        • body mass
          • large animals sleep less
        • Brain mass
          • more REM sleep
        • animals with exposed sleep sites
          • sleep less
        • herbivores sleep less than carnivores
      • observational research for about 54 species
      • approach takes in ecological and physiological factors
        • cannot be regarded as reductionist because it explains sleep in terms of the whole animal and its environment
      • high ecological validity
    • Allison studies sleep in 39 species
      • prey animals sleep for significantly less time than predators
        • Meddis believes that sleep leaves an animal unreactive and vulnerable
          • if safety was the only consideration then sleep would not exist
        • anomalies such as rabbits have a high danger rating but sleep as much as turtles which have a low danger rating
    • hibernation/ energy conservation
      • Basal metabolic rate (bmr) -the rate of energy consumption- is positively correlated to sleep
        • Lima and rattenberg
        • small animals have a higher BMR than larger animals and so they sleep more
    • Energy conservation
      • warm blooded animals (mammals) need a lot of energy of maintain a constant temperature
        • sleep serves the purpose of providing a period of enforced inactivity and uses less energy
    • keep out of the way of predators
      • Meddis et al
      • animals can hide themselves in the dark and not draw attention to themselves
      • Siegel also concluded that it reduces injury
    • NREM and REM
      • energy conservation only drops in NREM
      • Cicchetti found that larger has less NREM sleep but not less REM sleep
      • further argument that primitive animals such as most reptiles only have NREM sleep
        • REM sleep evolved more recently and may of been to maintain brain activity
        • while NREM sleep might of been evolved first for energy conservation
    • Capellini
      • criticised previous research for not having standardised date collection methods between species
      • meta- analysis of studies only using standardises procedures
        • eg lab conditions or habituated animals
      • found a negative correlation between metabolic rate and sleep
        • smaller animals have higher metabolic rates and sleep less
        • disproves energy conservation theory
        • but supports foraging being a main factor into sleep
          • higher metabolic rate or low energy diet decreases sleep time
      • predators sleep more but also species who sleep socially also sleep more
    • Unilateral sleep
      • sleep patterns can be an adaptive response to selective pressures
      • this is when only one half of the hemisphere of the brain sleeps
        • for example dolphins need to swim to the surface frequently for a breath
          • a dolphin the feel into SWS would drown
        • the two hemispheres of the brain swap over every two to three hours
          • allow the dolphin to survive without disturbing sleep patterns
    • evolutionary approach
      • fails to incorporate sleep deprivation
      • horne
        • proposed that we have core and optional sleep
          • core is vital sleep that is required for the body and brain functioning
          • optional is REM sleep and is dispensable
            • occupies unproductive animals and conserves energy
        • combines elements from evolutionary and restoration approach

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