Outline and evaluate one or more evolutionary explanations for the functions of sleep. (24)

Intro: * Behaviors evolve, develop if they provide selective advantages for the animal * Sleep=evolved into an essential behavior and serves an adaptive purpose in the EEA
Because it provides Selective Advantages * In other words sleep either provides some biological functions or it has other benefit * There are different explanations explaining the functions of sleep

P1: * First one being Energy Conservation * Mammals need to expend a lot of energy to maintain a constant body temp * This is particularly problematic for small animals with high metabolic rates as they use more energy * Webb 1982’s hibernation theory of sleep:
Sleep serves the purpose of providing a period of enforced inactivity thus conserving energy, which would be more efficiently spent at other times (e.g. during the day when it’s easier to find more food)

Supported by: * Rechstaffen (1974): * Found -ve correlation between the metabolic rate of animals and amount of sleep they have
So supporting Webb’s theory that animals need to sleep to avoid depleting all their energy and dying

BUT: * These studies=criticised as being correlational
-Does not necessarily provide a cause and effect between sleep and metabolism
-It doesn’t necessarily mean sleep=a consequence of a high metabolism when it could be the other way around
-E.g. sloth is a large animal, has low metabolic rate, yet it sleeps for 20 hours a day
Suggesting there are extraneous variables which are not taken into account, therefore lessening the internal validity of these studies

P2:
+ Capellini et al (2008) in a study:
-Found that smaller animals with higher metabolic rates
-Sleep less than larger animals with lower metabolic rates
-Therefore contradicting Webb’s theory

However: * This data supports the view that there’s a tradeoff between sleep and foraging * If sleep=a necessity, time spent sleeping may be constrained by food requirements * As herbivores e.g. cows eat plants, relatively low in nutrients therefore don’t sleep much to make up eating time * Whereas carnivores such as cats eat food high in nutrients which allows them to sleep more * Meaning that greater foraging requirements due to higher metabolic rate/diets of low energy
Creates a restraint on time available for sleeping

Therefore: * Capellini’s study and foraging function of sleep=more likely to be valid * As there were methodological issues in Rechstaffen’s energy conservation study * Rechstaffen’s research=flawed because the methods used to collect data on sleep in different animals=not standardized * Therefore comparisons between species=meaningless * On the other hand Capellini carefully selected data from studies only using standardized procedures in lab conditions
Making research into sleep for foraging requirements more internally valid and credible as an explanation

P3: * Another explanation of the evolutionary function of sleep
=Predator Avoidance * Predators sleep longer as there being less of a risk of being eaten/killed * Prey sleep less they must remain vigilant to avoid predators * So sleep therefore must serve vital functions because if not, natural selection would have eliminated it given the fact that it puts survival at risk

Supported by: * Allison and Cicchetti 1976: * Found species who had higher risk of predation did sleep less

BUT: * They also found exceptions * Rabbits who have high danger rating slept as much as moles who had a low danger rating * Goes against the Predator and Prey status * As it implies sleep may not be evolutionary but actually biologically essential * Thus showing it could be nature rather than nurture

P4: * In addition, Meddis 1995 tried to explain the evo. Function of sleep * Proposed the ’Waste of time’ hypothesis * Saying sleep serves the purpose of helping animals to stay away from predators when they are most vulnerable * Sleeping in hidden places allows animals to avoid predators by staying still when they have nothing better to do with their time

Suported by: * Siegel 2008: * Being awake=far risker due to exposure to predators/likelihood of being injured * He also suggested:
The only possible explanation for function of sleep is that
It enables both energy conservation and keeping us out of danger

Later: * Young 2008: * Supports that sleep does serve an evolutionary function * He studied little brown bats * Found that they only wake for a few hours a day to feed before going back to sleep * Meaning sleep aids survival

BUT: * If animals only wake to feed and reproduce before going back to sleep * Then this should be universal in all animals * But in fact this isn’t the case * So Young’s view=reductionist * As he thinks sleep is simply an adaptive response but takes no account why some species e.g. human don’t sleep when they are fed * Therefore making sleep as an adaptive behavior limited

Conclusion: * The evolutionary approach lacks falsifiability and relies heavily on evidence from the animal world
And in most cases evidence doesn’t always support a function of sleep, yet it doesn’t necessarily prove it wrong

* As a result, research into evolutionary explanations of sleep=generally unreliable and low in external validity
As not all animals will adhere to the same adaptive principles