Sleep Evolved Before Brains. Hydras Are Living Proof

Some of nature’s simplest animals suggest that sleep evolved long before centralized nervous systems.

The hydra is a simple creature. Less than half an inch long, its tubular body has a foot at one end and a mouth at the other. The foot clings to a surface underwater—a plant or a rock, perhaps—and the mouth, ringed with tentacles, ensnares passing water fleas. It does not have a brain, or even much of a nervous system.

And yet, new research shows, it sleeps. Studies by a team in South Korea and Japan showed that the hydra periodically drops into a rest state that meets the essential criteria for sleep.

Original story reprinted

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