Evolutionary Explanations

Evolutionary Explanations

Knowledge

Energy conservation

> Warm-blooded animals need to expend a lot of energy to maintain a constant body temperature, which is very problematic for small animals with high metabolic rates (such as mice) - all activities use energy & animals with a high metabolism use more.

> Sleep serves the purpose of providing a period of enforced inactivity (therefore using less energy) much as hibernation is a means of conserving energy. Webb described this as the 'hibernation theory' of sleep.

Foraging requirements

> If sleep is a necessity, the time spent sleeping may be constrained by food requirements - an animal has to gather food.

> Herbivores (cows) spend their time eating plants (grass) which is relatively poor in nutrients - as a result they must spend a lot of time eating and consequently can't 'afford' to spend time sleeping.

> Carnivores (cats) eat food that's high in nutrients and so don't need to eat continuously - therefore they can 'afford' to rest a lot of the time & by resting they can conserve energy.

Predator avoidance

> If an animal's a predator it can sleep for longer - for prey species sleep time is reduced as they must remain vigilant to avoid predators - logically they shouldn't sleep at all but if sleep's vital then they're best to sleep when least vulnerable.

Waste of time

> MEDDIS was the 1st to propose the 'waste of time' hypothesis - sleep helps animals stay out of the way of predators when most vulnerable (for most this means sleeping during the night in places they'll be hidden) - sleep ensures animals stay still.

> SIEGEL concurs with Meddis's view and claims that being awake is riskier than being asleep based on what we know about sleep patterns - energy conservation as well as hiding.

> YOUNG says 'in the wild, the best strategy for passing on your genes is to be asleep for as long as you can get away with... and that is exactly what you see'.

> The little brown bat is awake a few hours each day, when the insects that it feeds on are awake - it might be expected that the bat would sleep little because it's small but it doesn't. It's awake when it needs to be.

Evaluation

Energy, foraging or predation? 

Support for energy conservation - 

> ZEPELIN AND RECHTSCHAFFEN found that smaller animals with high metabolic rates sleep…