Whatever sleep does, it's something nature has had a tough time optimizing out despite the extreme vulnerability it creates and the sacrifice of a little under half an organism's waking time.
That should tell us it's something incredibly important that's hard to do any other way.
Edit: on the other hand... if Earth had two suns and rarely had periods of darkness, you wonder if maybe there would have been more evolutionary pressure to find another way.
Alternately, sleep is the optimal ultra-high-efficiency survival state and wakefulness only exists to give creatures enough time to get their affairs in order so that they can safely return to dormancy.
It's easy to think of sleep as a compromise to be defeated because we're culturally preoccupied with the achievements and pleasures of wakefulness, but that's really just us claiming personal preference for one narrow part of a holistic system that's just doing its own survival and propagation thing.
Consider trees, mushrooms, cicadas, snakes, or cats. Chilling out in low power mode as much is possible is maybe not a error to be fixed so much as it is an outcome of efficient design.
The default and optimal state of a life form is waiting and efficiently using resources.
Moving around, socializing and reproducing,
killing and eating, are all energy expenditures or necessary to be able to prolong the sleep-life. Annoyances, from the POV of the sleep-being.
"Hurry up and idle" for CPU design ended up being great for power efficiency. Nature came to the same conclusion for biological organisms a long time ago.
Consider hibernation. Evolution went to great trouble there to maximize the duration that some animals can sleep for - and it's pretty clearly solely designed to save power.
Which doesn't mean that's the only thing sleep is good for, evolution doesn't believe in separating concerns, but it's definitely a thing it does.
I wonder if we looked at really basic life forms like bacteria, would we find things akin to sleep at that level? What about next up in sophistication?
Yeah. Nature is the ultimate form of science. At any moment, it's incorporating an infinite amount of science, most of which we likely haven't discovered yet, and may not discover for millions of years - if ever.
Nature developed over millions of years of trial and error.
Seems likely like the need for sleep then selects for many social/group behaviors. “Solo self-found” is not really an option unless you’re really good at hiding or have some other tricks
That should tell us it's something incredibly important that's hard to do any other way.
Edit: on the other hand... if Earth had two suns and rarely had periods of darkness, you wonder if maybe there would have been more evolutionary pressure to find another way.