Why do we sleep evolutionary theory
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Why do we sleep? – Evolutionary Theory. BATs AO1 – Understand and recall the ecological theory of sleep A02 – Analyse information and relate it to psychological theories - Use information from psychological research to evaluate the theories. Good old synoptic points!!.

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Why do we sleep? – Evolutionary Theory

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Why do we sleep evolutionary theory

Why do we sleep? – Evolutionary Theory

BATs

AO1 – Understand and recall the ecological theory of sleep

A02 – Analyse information and relate it to psychological theories

- Use information from psychological research to evaluate the theories

Good old synoptic points!!

Approaches - Evolutionary , comparative

Issues - use of non-human animals, Debates - Reductionism

Methodology – problems with the Phylogenic sleep project


Theories of sleep

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

psychlotron.org.uk


Hibernation theory

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)

    • Read and complete the worksheet – Ecological Theories of Sleep

psychlotron.org.uk


Animal sleep patterns

Animal sleep patterns

Sleep patterns vary by species

3hrs

4hrs

8hrs

16hrs

20hrs

psychlotron.org.uk

less

more


Evidence

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

psychlotron.org.uk


Evidence1

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)

psychlotron.org.uk


Problems

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?

psychlotron.org.uk


Problems1

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?

psychlotron.org.uk


Evaluation of evolutionary explanations

Evaluation of Evolutionary explanations

  • A criticism of all evolutionary explanations is that arguments about adaptiveness and natural selection are made post hoc (‘after the fact’ – after it happened).

  • We assume the sleep (and sexual selection!) is adaptive because they are still around today.

  • But they may just be neutral and not selected out or linked to another adaptive behaviour.


Evaluation of evolutionary explanations1

Evaluation of Evolutionary explanations

  • The ecological (evolutionary) theory of sleep is the same as Circadian theory!

  • Circadian rhythms evolved to induce sleep at appropriate times of day – so they are linked.


Waste of time theory meddis1975

Waste of Time Theory – Meddis1975

  • Read p 14 – Waste of time and Cutting Edge and p15 – Unilateral sleep

  • What did Meddis propose?

  • Why did Siegel and Young (2008) support Meddis.

  • What other explanation does their idea have for why bats sleep so little?

  • What methodological issues are there with the Phylogeny of Sleep project?

  • Why have some species adapted Unilateral sleep?


A summary of the hibernation ecological theory of sleep

A summary of the Hibernation/Ecological Theory of Sleep

  • Compare the ideas of Webb (1982) and Meddis (1975) – worksheet matching activity

  • What evidence is there to support the predictions outlined on the worksheet (Ecological Theories of Sleep)?

  • What evidence is there that challenges these ideas?

    You can also use p 14-15 and the Worksheet ‘Theories of sleep – Hibernation theory’


Lets have a debate

Lets have a debate!!!

  • Which do you think is the most plausible theory for why we sleep?

  • Jot down the pros and cons of each theory

  • Choose either the Restoration or Evolutionary Theory.

  • Share all the good points you van think of with others who have chosen the same Theory

  • Be prepared to speak in a debate!!


Extension activity

Extension Activity

  • Read Horne’s interview and page 15 – A combined approach

  • Why might the Restoration theory and Evolutionary theory be thought of as Reductionist?

  • How does Horne’s theory address this problem?


Homework

Homework

  • Discuss evolutionary explanations of the function of sleep. (9+16 marks)

  • You can use the Restoration theory for A02 material as long as it is relevant.


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