Evolutionary Explanations of Sleep - Psychology A Unit 3 A2 Edexcel

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Evolutionary Explanations of Sleep
Capellini et al 2008: methods used to collect data on sleep in different animals were not standardised and
therefore comparisons between species were meaningless
Energy Conservation ­ mammals need to expend a lot of energy to maintain a constant body temperature; all activities use
energy and animals with high metabolic rates use even more energy
Webb 1982: hibernation theory ­ sleep serves the purpose of providing a period of enforced inactivity, much as
hibernation is a means of conserving energy
Zepelin and Rechtschaffen 1974: smaller animals with higher metabolic rates sleep more than larger animals,
supports view that energy conservation may be the main function of sleep
Sloths sleep for 20 hours a day, and so are an exception to Zepelin and Rechtschaffen's findings
Capellini et al 2008: negative correlation between metabolic rate and sleep ­ smaller animals have higher metabolic
rates and less sleep, suggests energy conservation hypothesis may be wrong
Foraging Requirements ­ time spent sleeping may be restrained by food requirements. E.g. cows and horses (herbivores)
spend a lot of time eating food low in nutrients, such as grass, and therefore spend a great deal of time eating and don't
have time to sleep. Conversely, cats and dogs (carnivores) eat foods high in nutrients so do not need to eat continuously,
meaning they have longer time in which they can sleep, and by sleeping they conserve energy.
Capellini et al 2008: data supported view that there is a trade-off between sleep and foraging; greater foraging
requirements creates a resistance on time available for sleeping
Lack of research evidence
Predator Avoidance ­ if an animal is a predator, it can sleep for longer, whereas prey species cannot, as they must remain
vigilant to avoid predators. Ideally, this would mean they should never sleep, but as sleep is a vital function, they must sleep
at a time when they are least vulnerable.
Allison and Cicchetti 1976: species with a higher risk of predation slept less, though there were exceptions such as
rabbits, who were high risk, yet slept as much as moles, who were low risk
Waste of Time ­ sleep helps animals to stay out of the way of predators during the time of the day they are most vulnerable
Meddis 1975: sleep may simply ensure that animals stay still when they have nothing better to do with their time
Siegal 2008: being awake is riskier than sleeping because an animal is more likely to be injured; sleep enables both
energy conservation and keeping an individual out of danger
Ignores restoration theory (Oswald 1980) (biological approach) that the main function of sleep is for the body to
undergo its natural recovery process i.e. protein synthesis and cell growth
Combined Approach ­ Horne 1998: suggested a combined approach that combines elements of both restorative and
adaptive theories. There may be a distinction between core and optional sleep, with core sleep (SWS) being a vital portion
of sleep that an organism requires for the body's natural recovery process, and optional sleep (REM and some NREM)
functioning as a way of occupying unproductive hours, and, in the case of small mammals, conserving energy.


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