As far as I can find online, we only burn about 15% less calories sleeping compared to being awake but stationary (say, lying in bed). It seems hard to believe that sleep came to be so universal primarily for such a minor benefit, especially considering the downsides of being so vulnerable, no?
Good to have a number for this. Though I think a better counterfactual is between sleeping and actively foraging. Foraging + thermoregulation costs even more calories.
But let’s say for the sake of argument that being awake + foraging takes 20% more calories compared to sleeping. Would sleeping actually get selected for? I think so. Evolution can make pretty fine distinctions given enough generations.
For example, cavefish (who live in an environment without light) quickly evolve less pigmentation and underdeveloped eyes to save energy. This is a convergent trait, it’s been observed in several different species. Though I’m not sure what kind of energy penalty eyes and pigment have.
If we’re just talking calories, the necessary condition for sleep to be advantageous should be that the calories obtainable at night aren’t sufficient to cover the caloric cost of being active. With your 20% example and 16 hours of foraging, daytime foraging must have provided at least (16+8*80%)/16 = 140% of the calories it cost, meaning that even being able to obtain one seventh the calories foraging at night would pay for the extra cost relative to sleep. Intuitively, it seems like most animals would be able to do this and would get more calories from not sleeping.
As far as I can find online, we only burn about 15% less calories sleeping compared to being awake but stationary (say, lying in bed). It seems hard to believe that sleep came to be so universal primarily for such a minor benefit, especially considering the downsides of being so vulnerable, no?
Good to have a number for this. Though I think a better counterfactual is between sleeping and actively foraging. Foraging + thermoregulation costs even more calories.
But let’s say for the sake of argument that being awake + foraging takes 20% more calories compared to sleeping. Would sleeping actually get selected for? I think so. Evolution can make pretty fine distinctions given enough generations.
For example, cavefish (who live in an environment without light) quickly evolve less pigmentation and underdeveloped eyes to save energy. This is a convergent trait, it’s been observed in several different species. Though I’m not sure what kind of energy penalty eyes and pigment have.
https://en.wikipedia.org/wiki/Cavefish
If we’re just talking calories, the necessary condition for sleep to be advantageous should be that the calories obtainable at night aren’t sufficient to cover the caloric cost of being active. With your 20% example and 16 hours of foraging, daytime foraging must have provided at least (16+8*80%)/16 = 140% of the calories it cost, meaning that even being able to obtain one seventh the calories foraging at night would pay for the extra cost relative to sleep. Intuitively, it seems like most animals would be able to do this and would get more calories from not sleeping.