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At first glance, humans seem to have very little in common with Cassiopea, a primitive jellyfish. Cassiopea is brainless, spineless and spends essentially its entire life sitting upside down on the ocean floor, pulsating every few seconds. However, scientists have now discovered that, as different as our daily schedules may seem, humans and jellyfish actually start and end their days with the same behavior: sleep.
This finding that jellyfish sleep implies that sleep is an ancient behavior, largely untouched by millennia of evolution.Image credit: Caltech
