> we don't know why we sleep
Garbage collection, for one thing. Transfer from short-term to long-term memory is another. There's undoubtedly more processes optimized for or through sleep.
Garbage collection, for one thing. Transfer from short-term to long-term memory is another. There's undoubtedly more processes optimized for or through sleep.
Worse, evolution clearly can get around this, dolphins have a trick that lets them (air-breathing mammals living in water) be alert 24/7, so why didn't every other creature get that? What's the thing that dolphins fail to get, where the cost of its absence is only worthwhile when the alternative is as immediately severe as drowning?
Sure, there's flaws with what evolution can and can't do (it's limited to gradient descent), but why didn't any of these become dominant strategies once they evolved? Why didn't something that was already nocturnal develop the means to stay awake and increase hunting/breeding opportunities?
Why do insects sleep, when they don't have anything like our brains? Do they have "Garbage collection" or "Transfer from short-term to long-term memory"? Again, some insects are nocturnal, why didn't the night-adapted ones also develop 24/7 modes?
Everything about sleep is, at first glance, weird and wrong. There's deep (and surely important) stuff happening there at every level, not just what can be hypothesised about with a few one-line answers.
And the answer to "Why not always awake?" is very likely "Irreversible decision due to side effects". Core system decisions like bihemispheric vs unihemispheric sleep can likely only be changed in relatively simple lifeforms because the cost of negative side effects increases in more complex lifeforms due to all the additional systems depending on the core system "API".