Comment by cubefox
4 days ago
Yeah. Perhaps animals are the first organisms that developed the ability to be awake, not the first that developed the ability to sleep.
By the way, even Cnidaria (jellyfish etc) exhibit sleep-wake cycles [1]. They don't have a brain, but they do have a nervous system. Maybe the first animal with nervous system (a common ancestor of Cnidaria and Bilateria) was the first to have a sleep-wake cycle.
I don't understand the current research on mitochondria, but it sounds as if sleep has to do with how neurons work.
1: https://link.springer.com/chapter/10.1007/978-3-031-62723-1_...
That's actually very interesting. The most convincing explanation for also I've heard is it's just a result of living in a planet that is cold and dark half of the time. It makes sense to use that time to recharge. I wonder how much sunlight would factor in for something like a jellyfish.