One of the key criticisms made, in relation to evolutionary theories of sleep, is that many of them suggest that animals sleep in order to waste time. Whereas the restoration view is that sleep is not wasting time but offers the opportunity for key functions to take place. A second criticism is that evolutionary theories may not be suitable for explaining human sleep. Sleep may have been adaptive during the environment of evolutionary adaptation but this hasn’t been true for a long time and one wonders why humans haven’t evolved different patterns of sleep.
Outline and evaluate one or more research studies relating to the theory of sleep that you have outlined.
Sleep is likely to serve some adaptive function. Meddis proposed that the function is a protective one. When animals do not have to be out and about finding food, then it would be adaptive for them to be quiet and hidden. At the same time animals that are likely to be preyed upon would be better off sleeping very little whereas predators can afford to sleep a lot because they are not in much danger. Observations of the animal world would support this. Predator species, such as cats, sleep a lot more than prey species such as mice.
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On the other hand, one might argue that predators need to spend a lot of time finding food so of they sleep a lot they may go hungry. In addition herbivores have to spend a lot of time finding food and will sleep little. The cow is not preyed upon and sleeps only a little. The point is that the evolutionary argument can be used to explain almost any sleep pattern.
Another evolutionary explanation was suggested by Webb. This is the hibernation theory. This theory suggests that sleeps adaptive because when an animal is asleep it is not using up energy. For most animals finding food is their biggest problem so that there is a vicious cycle, the more active the animal is, the more food has to be found; the more food finding, the more energy is used. When an animal hibernates or sleeps this reduces the amount of food that is needed and would increase survival.
Evolutionary theory can be used to explain why different animals sleep in different ways. For example one species of dolphin sleeps one hemisphere at a time possibly in order to maintain consciousness of debris in the environment in which they live.
Certainly some aspects of sleeping are adaptive; however, it may not be the main function of sleep. The alternative theory is the restoration theory, which proposes that all animals sleep because certain functions take place during sleep which help the animal restore itself physiological and psychological restoration can take place when an animal is relaxing, so why then is it necessary to become unconscious during sleep? In terms of protection one would think it is more adaptive for animals not to lose consciousness. Perhaps the reason is that for good restoration to take place the brain has really got to go off-line.
Neither theory accounts for why animals lose consciousness when sleeping. Sleeping my not be necessary for restoration, and from an adaptive point of view it makes little sense. Horne made the important point that sleep probably serves different purposes in different species. Thus, no single theory is likely to be adequate.
