system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we need so much sleep?

What physiological and psychological processes are our bodies going through that take so long?
gpt
Physiologically, we're not completely sure. But there are theories such as:

* Keeps us out of trouble at night (dangerous time).
* Conserves energy during a time that it's inefficient to be hunting/gathering
* Allows for restorative processes, muscle repair, protein synthesis

Psychologically, we're also not sure! But it seems fairly certain that during sleep the brain clears adenosine build up. Think of adenosine as lactic acid for the brain, it builds up when we work our brains and then needs to be processed.

There's also lots of promising research indicating that sleep has a very close connection to neuro-plastic functions like learning and memory.