This is a fascinating article that illustrates that sleeping is a more complex activity than we know: Sleep Evolved Before Brains. Hydras Are Living Proof. | Quanta Magazine
I’ve always associated sleep with something our brains need to have in order to survive. (Sleep deprivation is one proof of that.) But I have been won over to the idea that sleep is a more fundamental property of living things, brain or no brain.
Read the article: I think you’ll find it fascinating too.