Jellyfish and Sea Anemones Sleep Just Like Us

Jellyfish and sea anemones sleep like us

By Claire Cameron edited by Andrea Thompson

Jellyfish and sea anemones are curious creatures: These organisms evolved without brains and, as scientists have only discovered in recent years, do not need them to sleep. Animals, however, have neurons, nerve cells that appear interconnected throughout their bodies. And now a new study shows that the way these animals sleep is strikingly similar to humans, suggesting that sleep may have evolved before even the most primitive brains.

The results, published Tuesday in Natural communications, also help answer one of the dominant mysteries of science: why do animals sleep? They add to previous evidence from other animals and humans that sleep provides a “window” for brain and body maintenance, helping to repair DNA damage and maintain neuronal health.

“This confirms that sleep opens a window for key household tasks,” says Philippe Mourrain, associate professor of psychiatry and behavioral sciences at Stanford University, who studies sleep. Mourrain was not involved in the new study.

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The new work shows that this function of sleep has been conserved throughout evolution, he says, from animals, like primates, which have one of the most complex brains, to cnidarians, like jellyfish, which do not.

Intriguingly, the study reveals that jellyfish appear to enter a sleep state for around eight hours a day and usually at night – a schedule that many humans might recognize. Sea anemones also appear to sleep about a third of the day.

The researchers also showed that when these animals’ neurons experienced additional team-induced damage, they slept more, a finding that Mourrain says provides clues about what causes us to fall asleep in the first place.

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