Why sleep is such an important part of our lives? …and on a related note, why is bedtime so important? Based on what our bodies (and other animal bodies) accomplish while sleeping, there are a few leading theories about why we sleep.

From PBS Digital Studios’ The Good Stuff, find out about those theories, learn how humans have slept in the past, and visit Chicago’s Lincoln Park Zoo and Shedd Aquarium to learn about how animals like sharks, dolphins, snakes, and rhinos sleep completely differently than we do.

Watch this next: The benefits of a good night’s sleep.

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