In a heartwarming reminder of how connected all life on Earth truly is, researchers have discovered something extraordinary: jellyfish sleep just like we do—even though they don't have brains at all!

Published in Nature Communications, this groundbreaking study reveals that both jellyfish and sea anemones experience sleep patterns strikingly similar to humans, offering beautiful new insights into one of nature's most fundamental processes.

"Neurons are very precious," explains study co-author Lior Appelbaum, a molecular neuroscientist at Bar-Ilan University in Israel. "They don't divide, so you need to keep them intact." This discovery suggests that sleep evolved primarily to protect and repair our nerve cells—a function so important that it predates the evolution of complex brains.

The upside-down jellyfish, with its poetic scientific name Cassiopea andromeda, sleeps approximately eight hours daily, mostly at night—just like many humans! Even more delightfully, these graceful creatures enjoy a short midday nap, proving that the siesta is truly a natural phenomenon.

Meanwhile, the starlet sea anemone prefers to catch its rest around dawn, sleeping for about one-third of each day. This marks the first time scientists have characterized sleep in sea anemones, expanding our understanding of how widespread this essential behavior truly is.

"Every time somebody adds to the list of species that sleep, it is a very important step for the field," enthuses Chiara Cirelli, a sleep researcher at the University of Wisconsin–Madison. The growing list of sleeping creatures demonstrates just how universal and vital rest is to life itself.

This research builds beautifully on earlier work from 2017, when scientists first identified sleep-like states in jellyfish. "There is good evidence that sleep emerged with neurons," says Ravi Nath, a postdoctoral neuroscientist at Stanford University. "There is likely a core function, but each species has also adapted sleep to meet its own needs."

The implications are both profound and comforting. Sleep is such an essential function that evolution has preserved it across every animal with a nervous system studied so far. Even though sleeping leaves animals vulnerable to dangers and takes time away from finding food or caring for young, nature has deemed it absolutely necessary.

By studying these simple yet remarkable creatures both in laboratories and in their natural habitat in Key Largo, Florida, scientists are uncovering the deep roots of a behavior we all share. The fact that creatures with such simple nervous systems require sleep tells us something important: rest isn't a luxury—it's a fundamental requirement woven into the very fabric of life.

This discovery reminds us that even the most delicate jellyfish drifting through the ocean shares something profound with us. We're all part of the same incredible story of life on Earth, connected by our shared need for restorative rest.