More on theories of sleep

More on theories of sleep – from http://www.psychology4a.com/biological_rhythms.htm

Evaluation of the Meddis ‘Protection Theory’ of sleep

1. Seems logical; appreciates the complexity of the relationship between sleeping, predator-prey relationships, and body size (whereas the Webb theory was simplistic) (+ve)
2. Prey animals are very vulnerable when asleep, so unless live in safe burrows they are more - not less - at risk sleeping. (-ve)
3. Theory predicts prey animals should sleep longest, to keep safe from predators - but opposite is true.  Horses sleep little, lions sleep a lot (-ve)
4. Sleep isn’t just about protection and body size - involve food requirements as well (herbivores such as horses eat very poor quality food, so have to stay awake long enough to eat enough; carnivores such as lions eat very high quality food, so don’t have to spend lots of time feeding and can afford the time to sleep) (-ve)

Other animals also more vulnerable sleeping.  E.g. Indus dolphin in danger of being hit by debris in river, and has had time to evolve blindness - so why not also time to evolve…