Evolutionary explanations for the function of sleep

Evolutionary Explanations of the Function of Sleep

What is the Evolutionary approach?

•          We know that sleep must be adaptive in some way, otherwise why do all animals do it despite substantial costs?

•          Either it provides some vital biological function, or it provides some other benefit.

•          The Evolutionary explanations aim to suggest what other benefits might be associated with sleep.

•          The evolutionary approach has also been called the ecological approach. It is called ‘ecological’ because it is based on observations of animals in their natural environment;

•          ‘Ecology’ is the study of animals in relation to their environment.

Differences

•          Although all animals sleep, patterns vary:

–        Nocturnal / Diurnal

–        Amounts of sleep

–        Amounts of REM / NREM

–        So there are different explanations within the evolutionary perspective

EVOLUTIONARY (ECOLOGICAL) EXPLANATIONS

•          Energy conservation

•          Predator avoidance

•          Foraging requirements

•          Waste of time

Energy Conservation

•          All activities use energy, and animals with high metabolic rates use even more energy.

•          Sleep, however, serves the purpose of providing a period of enforced inactivity (therefore using less energy)

In some animals, hibernation is a means of conserving energy. Webb (1982) described this as the hibernation theory of sleep

AO2

•          Availability of food: animals sleep more when food is scarce (Berger & Phillips 1995).

•          Zepelin and Rechtschaffen (1974) - smaller animals, with higher metabolic rates, sleep more than larger animals.

Predator avoidance

•          If an animal is a predator, then it can sleep for longer whereas prey species sleep time is reduced as they must remain vigilant to avoid predators.

•          if sleep is a vital function then they are best to sleep when least vulnerable.

•          Shrews in burrows & bats in caves can sleep more safely than antelopes or zebras on the open savannah

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•          Could sleep be more risky that quiet alertness? Are you more likely to be eaten if you’re asleep?

•          But research support (Allison & Cicchetti 1976; Lesku et al 2006)

–        predators have more total sleep time than prey

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