1. Theories of sleep Hibernation theory (Webb, 1974)
Evolutionary approach – sleep is assumed to confer a survival advantage
Sleep helps conserve energy by:
Reducing energy spent on behavioural activity
Drop in body temp & metabolic rate reduces energy lost as heat
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2. Hibernation theory
Main prediction is that an animal’s sleep pattern will be determined by its energy intake & expenditure pattern
Small animals will need more than large
Diet (e.g. carnivore vs. herbivore) will affect sleep patterns
Sleep will increase when energy loss goes up (cold) or energy intake goes down (food scarcity)
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3. Animal sleep patterns less more psychlotron.org.uk
Sleep patterns vary by species
3hrs
4hrs
8hrs
16hrs
20hrs
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4. Evidence
Comparative studies of different species generally support evolutionary view
Smaller animals tend to sleep more than larger (e.g. giraffe 1hr vs. bat 20hrs)
Carnivores sleep more than herbivores (e.g. lion 16hrs vs. buffalo 3hrs)
Some notable exceptions e.g. rabbit (small, herbivore) & human (much larger, omnivore) both sleep about 8hrs
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5. Evidence
Sleep patterns are affected by energy expenditure & availability
Animals generally sleep more when weather is cold and food is scarce (Berger & Phillips, 1995)
However, no direct correlation between physical work done and sleep duration in humans (e.g. Horne & Minard, 1985)
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6. Problems
Many evolutionary significant factors could affect sleep patterns; theory doesn’t tell us which are important
Does a bat get so much sleep because it’s small or because it has few predators?
Why do animals with very different lifestyles have similar sleep patterns?
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7. Problems
Some features of sleep cannot be explained easily by the hibernation theory:
Why is sleep universal when in some species (e.g. dolphins) it would have been an advantage to get rid of it?
Why is sleep deprivation apparently fatal?
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