Evolutionary Explanations of Sleep

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  • Created by: rhallett
  • Created on: 29-10-15 11:47
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  • Evolutionary Explanations of Sleep
    • These argue that sleep evolved to help organisms adapt to their environment; hibernation.
      • Argues that sleep has NO important restorative function
    • Argues that sleep has NO important restorative function
    • 1) Meddis
      • Sleep protects animals from harm and predation by immobolizing animals during times of risk ie night
        • During evolution, humans would have slept during the night, when they would have been at risk of predation
    • 2) Webb
      • Sleep allows animals to conserve energy by reducing activity during times when it would not be useful
        • Particularly useful for small animals with high metabolic rates and warm blooded animals ie mammals as they use a lot of energy to maintain body temperature
    • 3) Siegel
      • Combines both theories: sleep allows energy conservation and predator avoidance
        • Little brown bats show this: only awake for a few hours a day to feed - supports as it suggests sleep aids survival and energy conservation
    • Evaluation
      • + Decoursey - damaged the SCNs of 30 chipmunks, disrupted circadian rhythms; returned to wild and observed over 80 days - more were killed because they were active and noisy at night - SUPPORTS MEDDIS
        • Unclear if these findings can be extrapolated to humans, sleep may have evolved to have different functions in two species
          • Unethical as the chipmunks were being harmed
      • + During sleep, body temperature drops - SUPPORTS WEBB
        • But the drop is very little thus little energy is conserved
          • During REM the brain is very active and uses a lot of energy,
            • Also unclear why animals need to be unconscious to conserve energy as this is dangerous for them
      • + Zepelin found smaller animals with higher metabolic rates slept more than larger animals - SUPPORTS WEBB
        • Yet there are many exceptions eg Sloths who are large and sleep for 20 hours a day
      • - Allison - studied 39 species, found that prey slept less than predators - DISPROVES MEDDIS
        • Sleep helps animals avoid predation; small animals can hide, animals such as giraffes cannot
      • One of the biggest problems is that many animals sleep, even when it appears it doesn't help them adapt to their environment
        • One species of dolphin has lost its ability to see and lives in the river Ganges, yet it still sleeps. Suggests a restorative purpose of sleep


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