Bees, sharks, anteaters, humans, we all share the need for sleep. Why we do it is of course still largely a mystery, but the fact of it remains incontrovertible. Now, new research on jellyfish is pushing the origin of sleep even further back down the evolutionary tree, before even the appearance of brains.
It’s long been known that any creature with a central nervous system needs to sleep, but jellyfish are effectively brainless. They do have neurons arranged into a “nerve net” throughout