[zyrthofar]

I like to think that we evolved sleep because it's better, in the wild, to be still and silent in the dark, than move around and make noise.

Since we can barely see in the dark and can't do anything anyway, wouldn't it be preferable to minimize the time spent defenseless against predators with better night vision? Staying still seems like a good strategy a lot of times, when most animal visions, night vision or not, is based on movement.

It doesn't answer, though, why the top of the food chain need to sleep too.

[ricree]

It also doesn't explain why the effects of sleep are so strong, when an instinct for watchful stillness would have been every bit as effective for that purpose.

[jqm]

Maybe if we hadn't been sleeping we would have evolved the ability to see in the dark by now.