[brazzledazzle]

I've found that it's best to not think that evolution optimizes for the best thing but rather that it optimizes for "good enough". Sometimes they are one and the same but they don't have to be.

Sleep could have started as a rudimentary adaptation to one thing and ended up being refined and coopted for other things.

[Freestyler_3]

Evolution is diverse, if all living things need sleep then I think its A: something that is absolutely needed, without it you wont survive [guaranteed] B: A left over from our common ancestor