Evolutionary Explanations

Evolutionary Explanations of sleep:

-Energy conservation

-Predator avoidance

-Foraging requirements

-Waste of time

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  • Evolutionary Explanations
    • Foraging Requirements
      • AO1
        • Time spent sleeping may be constricted by food requirements as an animal has to spend time gathering food.
        • Herbivores spend a lot of time eating so sleep less
        • Carnivores eat higher nutrient foods so can afford to eat less and spend time sleeping.
      • AO2
        • Tigers sleep for 15.8 hours whist cows sleep for 3.9 hours.
    • Waste of Time
      • AO1
        • Sleep helps animals stay away from predators when they're most vulnerable and don't need food.
        • Most animals sleep whilst it's dark, as it's riskier to stay awake and hunt when it's dark
          • Save energy and stay away from danger.
      • AO2
        • Horne - very little difference in energy conserved when we are asleep to when we are awake and resting.
    • Predator Avoidance
      • AO1
        • Predators can sleep longer than prey - not at risk.
        • Prey do sleep though, so there must be an evolutionary advantage.
        • Prey sleep when they're least vulnerable
      • AO2
        • Dolphins sleep with half a brain at a time.
          • Adapted so that they an stay safe
        • One species of Dolphin only sleep for a few seconds at a time
          • Less likely to be injured by debris
    • Energy Conservation
      • AO1
        • Activities use energy, animals with high metabolic rate use even more energy.
        • Sleep provides period of forced inactivity to conserve energy.
        • Some animals hibernate to conserve energy.
      • AO2
        • 53 species of mammals studied, those with high metabolic rates slept for longer. Smaller animals also slept for longer.
        • E.g A brown bat sleeps for 20 hours, whilst an elephant sleeps for 4 hours.
        • A sloth has slow mmetabolism and is large but sleeps for 20 hours
    • Overall Evaluation
      • Rats on a turn table.
        • Table starts to spin when their brain patters change - so they awoke and started to exercise. If they didn't they fell into the water.
        • Only had 16% of their normal sleep - became weak and lost weight even when they ate normally. Metabolic rate also increased.
        • Most experimental rats dies between 21-33 days
        • Couldn't rest to conserve energy.
        • May have died due to trauma.
        • Ethics - was it worth it?
      • Young - We only have sleeping patterns for 150/5000 mammals.
        • Still have lots of data to collect and compare.
        • Recordings are also conflicting - further research is needed.


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