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, Caltech 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.

From Listen to graduate students and study co-authors Ravi Nath, Claire Bedbrook, and Michael Abrams as they discuss their research on the Cassiopea jellyfish and its sleep-like behaviors—”the first example of sleep in animals without a brain.” Their nightly behaviors include a decrease of rhythmic bell pulsing, slower reactions to changes around them, and when kept active at night, a decrease in activity the next day.

Watch them without narration:

Related listening at SciFri: What Is Sleep? A ‘Superpower,’ a ‘Power Cleanse’.

Follow this with the benefits of a good night’s sleep and why do we sleep and how do different animals sleep? Plus: More jellyfish.

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