In a curious new study, scientists have found that sleep pre-dates the brain—meaning that animals don’t actually need a brain to sleep. In a tiny animal called the hydra, these researchers observed a “sleeplike state,” despite the fact that the hydra doesn’t actually have a brain. This provides “strong evidence that animals acquired sleep-related mechanisms before the evolutional development of the central nervous system and that many of these mechanisms were conserved as brains evolved.”

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