Don’t we? I could be wrong but my understanding is that the glymphatic system works very well during sleep. Basically excretory process of the central nervous system
No, we don't have a definitive answer. We are very good at describing what happens when we sleep and what goes wrong when we don't, and so there are a number of theories as to why we sleep. But a definitive answer? There isn't one (yet). Here is the most likely theory according to Wikipedia:
>The essential function of sleep may be its restorative effect on the brain: "Sleep is of the brain, by the brain and for the brain."[95] This theory is strengthened by the fact that sleep is observed to be a necessary behavior across most of the animal kingdom, including some of the least evolved animals which have no need for other functions of sleep, such as memory consolidation or dreaming.
>We are very good at describing what happens when we sleep and what goes wrong when we don't, and so there are a number of theories as to why we sleep
I'm not sure I understand the distinction you're trying to make. There's not purpose in a volitional sense in evolution, only effects. We sleep because necessary functions occur when we do and problems happen when we don't.
24 hour cycles are even observed in bacteria and archaea as well as the individual cells in our bodies. If I am understanding correctly, even in pure darkness bacteria will respond to 24-hour cycles of temperature change. Considering this, combined with the critical role of the microbiome in human health and the fact that our bodies tend to get 1-2 degrees cooler when we sleep, it seems our sleep/wake cycle may go even go beyond the brain.
I believe you're trying to assign a design intent behind sleep. Nature doesn't need this. We sleep because it works better than not sleeping, and that's all there is to it.
I thought the question was more along the lines of, "why do these things that happen during sleep require us to be asleep and not just happen all the time?"
What is being awake for? When we sleep and dream we connect with some kind of other dimension, incredible places. Animals seem to do as well. Maybe being awake just has the purpose of nourishing the body so that we can sleep, with sleep and dreaming being the meaning of life?
Or it is to conserve energy during the time that we are on the dark side of this spinning globe, since it is difficult to see in the dark.
We have good hints at the reasons : to repair cellular damage caused by reactive oxygen species. Clues pointing in this direction: animals without sleep survive with antixoydants and melatonine evolved as one.
