Oswald also suggested that SWS sleep was most important in restoration and repair. He found that during stage 4 of sleep, tissue growth, protein synthesis and the formation of red blood cells occur due to the release of a hormone from the pituitary gland. Research on infants (brain grows very fast) found that they spend most of time a sleep in REM sleep. Although protein synthesis is said to take place during SWS and REM sleep protein is need and protein only lasts around 4 hours in the body.
Sleep is also said to help physical restoration Hartmann 1973 found that people generally needed to sleep more during times of stress. It is also found that insomniacs tend to be very anxious, however it cannot be said that insomnia causes the anxiousness or the anxiousness causes the insomnia.
Another theory of sleep is the evolutionary theory. This is based on the idea that all animals sleep, but they sleep different amounts and at different times, and go into different stages of sleep. The reason for this is said to be because sleep has evolved to fit the ecological niche to which the animal belongs.
Meddis 1979 said that sleep has evolved to keep animals safe from predators, and to suit their needs and method of finding food. For example if an animal is at risk from a predator while it is a sleep, it will sleep very little and have a high metabolic rate. If an animal is safe while it is a sleep it will sleep more and conserve its energy. Empson critisised this theory as being “a waste of time” as this theory suggested that animals just sleep to waste time. As sleep deprivation studies has shown sleep plays a much more critical role, and could never just be a way of wasting time.
Animals such as dolphins that live under water but still need to surface to breathe cannot totally sleep, if they did they would die. Instead of fully sleeping bottlenose dolphin’s sleep with half a brain at a time, they are said to have adapted this way of sleeping to fit into their ecological niche.
Other animals such as reptiles which are cold blooded don’t have REM sleep, this has been suggested to be because REM sleep (dreaming) is used to keep the brain warm, as reptiles are cold blooded they don’t need to do this so they have evolved to not dream. This theory does not explain why some animals don’t fit the pattern, for example the giant sloth is large a slow yet sleeps for 20 hours a day. This theory also doesn’t explain why humans still require so much sleep when it would clearly be and advantage to humans to evolve to need less sleep.
There has not been much research to back up this theory as it is hard to back up any evolutionary theory, although it is not too far fetched to believe that animals evolving in this way, was to protect them from pray and to conserve energy.
Horne 1988 suggested that different animals may have different uses for sleep and that there may not be a universal function of sleep that fits all animals.
Faye Johnson 13.6