Evolutionary explanations of sleep Flashcards
Explain darwins theory in terms of sleep
Darwin’s theory of Evolution by Natural Selection says that behaviours will persist and increase in the population if they give an animal a survival advantage i.e. the animal that has that behaviour is likely to survive longer, therefore has a better chance of reproducing successfully and passing its genes on to its offspring. Sleep may promote survival in a number of ways and the pattern of sleep evolved by each species depends on its need to conserve energy, how vulnerable it is whilst asleep and the amount of time it needs to spend feeding.
Explain energy conservation - Webb
Sleep has survival value because it allows the conservation of energy (like hibernation). Warm-blooded animals expend a lot of energy maintaining body temperature, particularly if they are fairly small, with a high ratio of surface area to volume. During sleep body temperature drops so energy is saved, particularly if the animal sleeps in a warm nest or burrow. Sleep is therefore efficient in conserving energy when it is not being used to look for food or a mate.
Explain protection from Harm - Meddis
Sleep has survival value because it keeps the sleeper out of harm’s way and protects it from injury and predation during the time when it is not busy feeding or reproducing, and when it is most vulnerable.
- Animals with a safe nest or burrow (e.g. rabbits) can safely sleep longer than those that don’t (e.g. sheep)
- Animals that have few predators are safe to sleep for longer than those with many predators.
- Some animals (e.g. humans) are more vulnerable at night, others (e.g. bats) are not. In our evolutionary past night time would have been unable to forage, likely to fall and hurt ourselves and wide open to predation from species with better night sight. Sleep would have been an evolutionary advantage since it would have kept us out of harm;’s way. As a result, those members of the species that slept would have been more likely to survived to maturity and passed on their genes, ensuring that as an activity, sleep would have been retained in out behaviour repertoire.
Explain Type of Feeding
Herbivores’ food is lower in nutritional value, so they have to spend a large proportion of their time feeding, so less time sleeping. Carnivores’ food is more nutritious, so they need not spend so long feeding, and can conserve energy by spending more time asleep. Predators can also safely sleep for longer than prey species because they have less need to be watchful.
Evaluate Evolutionary explanations of the functions of sleep - Part one
There is much support for evolutionary theory, in terms of the sleeping patterns of animals. Diet is strongly correlated with sleep time, with herbivores (e.g. sheep) sleeping the least and carnivores (e.g. lions) the most, and the fact that sleep is seen in all mammals suggests that it is likely to be a product of evolution. However, there is also contrasting evidence from animals such as koalas, who do sleep a lot despite being herbivores. This seems to go against the diet strand of the evolutionary explanation but it consistent with energy conservation, as a low nutrition diet would mean the animal has less energy and so needs to sleep more. This illustrates how evolutionary theories do seem to explain the sleep patterns of most species, but to do this, they have adopted a catch all approach. If diet doesn’t work, then energy conservation will! this is a problem for the evolutionary explanation of sleep as it can;t explain almost any sleep behaviour and is so unfalsifiable. This means that it is not open to scientific testing, and is therefore unscientific. A related problem is that evolutionary theory explains behaviour “after the event” instead of predicting it. Rather then making predictions about behaviours that can be tested out, it explains behaviours that already exist, again making it less scientific an less useful.
Evaluate Evolutionary explanations of the functions of sleep - Part Two
the fact that animals such as dolphins appear to develop sleep adaptions specific to their environments suggests that there are evolutionary principles at work. for example, bottle-nosed dolphins switch off one hemisphere at a time, while Indus dolphins which need to be vigilant, sleep for between 4-60 seconds at a time. However, this suggests that sleep must have some other important biological function (rather than avoiding predation or conserving energy) and each species evolves a means of sleeping in such a way that doesn’t also threaten its survival. In the case of Indus dolphins, sleeping is dangerous. Surely it would be more adaptive for them not to sleep at all. Therefore, there must be other reasons why they need to sleep, and the restoration theory my offer a better explanation of this. The restoration approach is also better able to explain the complexities of sleep and the reasons for having five distinct stages of sleep (including the very bizarre REM stage) which evolutionary theory does not even attempt to explain. Evolution also fails to explain why sleep deprivation should have serious negative consequences, but studies suggest that it does. Sleep deprivation has long been used as a method of torture and Rechtschaffen found rats die if kept awake. Again restoration theory offers a better explanation of this.
Evaluate Evolutionary explanations of the functions of sleep - Part Three
The evolutionary explanations do not tell us why animals should become unconscious during sleep, rather than just resting. In humans, we save the calorific value of slice of bread by sleeping rather then resting. It would seem much safer to remain concious and therefore alert to danger, rather than sleeping. Furthermore, if sleep is designed to make us inconspicuous at night, it seems strange that snoring is so common in human sleep.
Finally, some have argued that sleep should now be pointless in most human societies because we have access to electric light, plenty of energy rich food and are able to protect ourselves against harm at night. However this change has come about very quickly (in evolutionary terms), particularly with the discovery of electricity. Evolution on the other hand is very slow, so we wouldn’t expect to see big changes in our sleep pattern for hundreds of years, due to the genome lag, it does seem to be the case that we now sleep significantly less than people did hundreds of years ago.
