Outline and evaluate one or more evolutionary explanations for the functions of sleep (4+16 marks)

There are two evolutionary explanations that discuss the functions of sleep, both of which offer explanations as to how the function of sleep has evolved to aid animals. Although there is evidence to support the claims made, the integrity of the explanations is questionable.

Meddis was the first to propose the predator avoidance hypothesis. He suggested that the primary function of sleep was for animals to be kept safe and to prevent attack from predators. This was an evolutionary development which aided natural selection as those who slept were out of harm’s way. The hypothesis is reasonable, if a prey is sleeping at night, it prevents predators from attacking. Meddis continued by suggesting the prey sleep in the parts of the day where they would be most vulnerable. This claim is supported as animals do generally sleep at night in hidden places to avoid attack. This is known as the ‘waste of time’ hypotheses. It claims that animals merely stay still when there is nothing better to do to avoid attack. These animals have lived on through natural selection by staying alive and sleep therefore evolved as a protective trait. Young supported the claims made by Meddis. He argued that being ‘asleep for as long as you can get away with’ was the best way of surviving and as a result, passing on ones genes. This is what occurs in the wild; for example bats are only awake for a few hours a day to feed, therefore Meddis’ predator avoidance theory may be valid.

However, there is large critique of Meddis’ theory. To start, there must be other functions of sleep apart from predator avoidance and to waste time. If there were no other functions of sleep, those who were in the most danger whilst sleeping would not sleep at all. Because all animals sleep, the must be an alternative function for this sleep. The restoration theory of sleep would support this criticism. The evolutionary theory fails to account how sleep may be used to restore the bodily functions of people. Instead, there are legitimate claims and supporting evidence to suggest that sleep may be used to restore our physical