Flashcards in Evolutionary Explanations Deck (18)
What is the general idea of evolutionary explanations?
Sleep is an adaptive function for survival
Name 3 key aspects about evolutionary explanations
1) Predator avoidance
2) Energy conservation
3) Foraging requirements
Outline predator avoidance for evolutionary explanations
Sleep is constrained by predation risk - predators sleep for longer (e.g. lion) - prey have to be more vigilant so sleep for shorter periods of time (e.g. zebra)
What did Meddis suggest about predator avoidance?
It helps animals to stay out of the way of predators during the day when they are most vulnerable - usually sleep during darkness
What supporting evidence is there for predator avoidance?
Allison & Cicchetti (1976) - found species with an increased risk of predation sleep less but there are exceptions like rabbits with very high danger rating yet sleep as much as moles with low danger rating
Outline energy conservation for evolutionary explanations
Warm blooded animals use a lot of energy to maintain a constant body temperature, this is particularly problematic for small mammals with high metabolic rates like mice - sleep is a period of enforced inactivity in which much less energy is used so helps to conserve energy, similar to hibernation
What supporting evidence is there for energy conservation?
Zepelin & Rechtschaffen (1974) - found smaller animals with higher metabolic rates sleep more (large surface area to volume ratio so lose more energy) but exceptions like sloths who are large animals yet sleep 20 hours a day
What evidence contradicts the idea of energy conservation?
Capellini - found negative correlation between metabolic rate and sleep (higher metabolic rate, fewer hours spent sleeping) so no support
What 2 negatives are there to the evidence which contradicts the idea of energy conservation?
1) It is a lab study and so not natural behaviour
Outline foraging requirements for evolutionary explanations
Sleep is constrained by food requirements as animals have to gather food - herbivores (cows) eat plants that are relatively poor in nutrients so forced to spend a lot of time eating and thus cannot 'afford' to spend time sleeping - carnivores (cats) eat food high in nutrients and thus do not need to eat continuously and can 'afford' to rest for much of their time, and also conserving energy
What supporting evidence is there for foraging requirements?
Capellini (2008) - greater foraging requirements (increased metabolic rate or diet low in energy) creates a restraint on time available for sleeping
Name 4 research studies for evolutionary explanations
1) Zepelin & Rechtschaffen (1974)
2) Horne (2001)
3) Pilleri (1979)
4) Rechtschaffen (1989)
Outline Zepelin & Rechtschaffen (1974)
Studied 53 species of mammals and found the higher the metabolic rate the longer they slept and the smaller animals tended to sleep longer - support
Outline Horne (2001)
Very little difference in energy conserved when asleep to when awake but resting, goes against as suggests sleep does not conserve energy
Outline Pilleri (1979)
Particular type of dolphin sleep for few seconds at a time as they are in constant danger - support for predator avoidance
Outline Rechtschaffen (1989)
Rats on a turn table and when patterns show they had started sleeping, started to turn so they woke up and exercised, otherwise fall in water. The rats only had 16% of usual sleep and were weak and lost weight even though they still ate (metabolic rate increased). Most died between 21-33 days which supports as high metabolic rate, needed to rest to conserve energy
Name and explain 3 negative points about evolutionary explanations
1) Animal studies
2) Sleep is maladaptive in survival terms - prey more vulnerable when asleep so doesn't prevent predation but it does make sense to suggest evolved to reduce danger of predation but unclear as to why sleep evolved to do tis
3) Behavioural inactivity would serve the same purpose