FUNCTIONS OF SLEEP EVOLUTIONARY EXPLANATIONS PSYA 3 A

FUNCTIONS OF SLEEP: EVOLUTIONARY EXPLANATIONS PSYA 3 A 2 Psychology Biological Rhythms and Sleep

How much do these animals sleep BAT GIRAFFE HORSE FOX CAT PYTHON LION ELEPHANT DUCK COW HUMAN (INFANT) DOG

How much do these animals sleep

Objectives • Today you will: • Consider different Evolutionary hypotheses for why we sleep • Consider the functions that sleep may provide from an evolutionary perspective • So that you can • Use this material to write 8 marks’ worth of AO 1 for the following question: • “Discuss evolutionary explanations of sleep” (8+16)

Why do we sleep? • In your groups, discuss reasons for why we need to sleep… • Your task is to come up with a hypothesis for the reasons why we sleep • Try to make it as psychological as you can • Remember the assumptions of the evolutionary approach!!!

Evolutionary Explanations • Sleep must be adaptive in some way as all animals do it, despite the fact that it carries substantial risks… • Evolutionary (or ecological) explanations aim to suggest what non-biological functions sleep may have for animals.

Energy conservation: Webb’s hibernation theory (1982) • Warm-blooded animals expend a lot of energy maintaining body temperature. • Those with high metabolic rates like mice, expend even more energy. • Sleep provides a period of enforced inactivity, therefore using less energy

Foraging requirements • If sleep is a necessity, the amount of time an animal can sleep is restricted by food needs. • Herbivores must spend a lot of time eating as their food is low in nutrients. • This means they can’t afford to spend a long time sleeping. • Carnivores eat highly nutritious food and so can afford to rest for longer. • This resting also conserves their energy.

Predator avoidance • Another possibility is that the risk of being attacked by a predator restricts the opportunity for sleep. • Predators can sleep longer, while prey need to stay vigilant so must stay awake longer. • This might suggest the best adaptation would be not to sleep at all, but if sleep is a vital function, it is best to sleep at times when they are least vulnerable.

Activity • You should now read over and discuss the questions on page 77 • Be prepared to share your answers on this!!!

Meddis’ (1975) Waste of time hypothesis • Sleep helps animals stay out of the way of predators during the day when they are most vulnerable. • Usually this means sleeping when it is dark, and in places where they will be hidden • Meddis suggests that sleep may simply ensure animals conserve energy when they have nothing better to do with their time.

Hours of sleep From the Phylogeny of Sleep database ‘Phylogeny’, means evolution – the evolution of sleep.

Meddis’ (1975) Waste of time hypothesis • Being awake is riskier than sleeping as animals are more likely to be injured. (Siegel) • Based on what we know about sleep patterns in different animals, the only possible explanation for sleep is that it enables energy conservation and staying out of danger.

Meddis’ (1975) Waste of time hypothesis • Young (2008) • “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” • For example bats are awake for a few hours, only when the insects it feeds on are awake. • It might be expected that as a small mammal, the bat would sleep little – but it doesn’t. It is only awake when it needs to be.

Activity • You should now read over and discuss the questions on page 76 • Be prepared to share your answers on this!!!

Gathering your AO 1 • You should now be able to write your 8 Marks worth of AO 1. • Try and split your writing between the two theories. • You should be writing about 200 words or so (as a rough guide!!)