1. Functions of Sleep: Evolutionary Explanations
PSYA3 A2 Psychology
Biological Rhythms and Sleep

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

3. How much do these animals sleep

4. “Discuss evolutionary explanations of sleep” (8+16)
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 AO1 for the following question:
“Discuss evolutionary explanations of sleep” (8+16)

5. 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!!!

6. 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.

7. 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

8. 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.

9. 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.

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

11. 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.

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

13. 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.

14. 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.

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

16. Gathering your AO1
You should now be able to write your 8 Marks worth of AO1.
Try and split your writing between the two theories.
You should be writing about 200 words or so (as a rough guide!!)