The evolutionary theory has been supported by looking into many different animals’ sleeping patterns and looking at the food chain. For example Meddis (1979) claimed that sleep evolved to keep animals safe and this is shown by the fact that predators such as lions and tigers sleep for much longer than prey animals such as cattle. However Siegel (2008) goes against this hypothesis, and suggests that being awake is actually riskier than sleeping because an animal is more likely to be injured because they are more vulnerable. However Meddis argues that sleep simply ensures that animals stay still when they have nothing better to do with their time. Siegel’s point is further supported by Bentley (200) who points out that if being still and unnoticeable is the great benefit and survival tactic of sleep then it is puzzling that so many humans sleep noisily, as shown by the fact that sleep walking and night terrors don’t keep us quiet and out of harm’s way.
The hibernation theory was proposed by Webb who suggested that sleep is important because it conserves energy. This has been supported by the fact that smaller animals lose heat faster and as a result sleep for longer than larger animals. However the main problem with the hibernation theory is that there are a whole host of evolutionary factors which can affect sleep patterns, for example prey animals are at greater risk of attack than predators and therefore how do we know which factors are important. There is no therefore no variation in sleep pattern that can’t be explained by using the evolutionary ideas. But there isn’t a way to decide which evolutionary factors are important. As a result Webb’s theory of sleep is unfalsifiable as it is not a scientific theory. There are also problems with the theories as whole. Sleep deprivation studies indicate that sleep has important functions and that some animals can die if sleep deprived, therefore keeping safe and energy saving may not be the main functions of sleep. This point is further supported by Empson (1989) who stated that the evolutionary theories are a ‘waste of time’ as they merely describe sleep as a means of passing time until it is safe to be active. As well as this it is strange that according to this theory NREM and REM and all their associated brain activity, serve no purpose at all.
The second theory is the restoration theory; this states that sleep is necessary to restore biological processes in the body. The main researcher into this theory is Oswald, who suggested that the function of sleep is to restore the body during periods when we are not active, to ensure bodily functions work effectively. Sleep allows physiological processes to rejuvenate the body and brain. The brain and body tissues are repaired and chemicals are restored. Therefore this theory suggests that when we are awake our body is damaged and certain chemicals become drained. Sleep allows us to rest and catch our breath after exercise. Slow wave sleep enables body repair and REM enables brain recovery. Growth hormone is released during slow wave sleep and enables protein synthesis and cell growth to rake place. The constant restoration of vital proteins is part of the body’s natural recovery process.
The restoration theory is plausible because we do need to get some rest every day and as a result the theory has some face validity. As well as this the theory has been supported by many case studies. Peter Tripp was a New York DJ who decided to not sleep for 8 days for charity. Towards the end, he experienced hallucinations and delusions. Every 90 minutes his hallucinations became more severe, like waking dreams or nightmares. This could have been when he would be in his REM sleep. Even though he was awake his brain was still in the sleep mode. This case study therefore supports the restoration theory because it shows how a lack of sleep can cause damage to the body because people need to relax to restore the biological processes within the body. However using case studies to support the restoration theory is problematic as they lack population validity because they tend to be of one person and as a result there are individual differences meaning conclusions cannot be met. As well as this many of the case studies on humans do not seem to support the idea that biological functioning is upset if a human is deprived of sleep as there are a lot of variations in the effects and is therefore difficult to make conclusions about the effects. On the other hand one can argue that case studies are a good research method as they are rich in detail.
The restoration theory also implies that after a physically hard day we will have to sleep more. This is supported by Shaprio et al. (1981) who found that people who had run a 57 mile race slept an hour and a half longer than they normally did for two nights after the race and there was a greater proportion of stage 4 sleep. This therefore is again consistent with the idea that sleep serves the purpose of restoring and replenishing biological processes. However evidence against the fact that physical exercise leads to sleeping longer comes from Horne and Minard (1985). They found that exercise just lead to people falling asleep quicker and not longer. Although there is further support for the restoration theory by Rechtshaffen et al. (1983) who placed a rat on a disc protruding from a small bucket of water with an EEG monitoring its brain activity. Every time brain activity indicated sleep, the disc rotated. Thus, forces the rat to walk if he didn’t want to fall into the water. After 33 days, all sleep-deprived rats died. This therefore supports the restoration theory’s view that sleep is important because it restores biological processes in the body and without it our bodies experience difficulties functioning. However this study was based on rats and as a result we may not be able to extrapolate the findings to humans because rats are biologically built differently. Also Young (2008) states that the more we know about sleep patterns the more research indicates that is environmental and not restorational factors that influence the function of sleep.
Both the restoration and the evolutionary approaches have their advantages. However the restoration theory seems more plausible because we do need to relax at some point of the day and the evolutionary theory seems to contradict itself. This is because according to the theory there are a number of factors that influence sleep patterns, these being, predator avoidance, conserving energy and eating habits, therefore which one is the most important? The evidence does seem to favour the restoration approach. This is because the example of dolphins (they sleep with half of the brain at a time) makes the restoration theory more valid because it lives in the water but breathes air and needs sleep it has evolved a special way of accommodating all these conflicting demands. As well as this the hibernation theory cannot explain why sleep deprivation can be fatal. Whereas the restoration theory does explain this as shown by case studies of people who have been deprived of sleep and as a result have experienced changes to their bodies due to the fact their biological processes have not been restored, (for example, Peter Tripp). Therefore there seems to be considerably more support for the restoration theory that sleep is important because it restores our biological processes in the body.
