The more primitive an animal looks, the less it seems to have in common with a human being. But scientific research in the field of the theory of evolution constantly gives scientists hints that in reality this is not quite so. Here and jellyfish were similar to us a little more than it might seem. It is about the ability of these hydroids to “fit” to sleep.

We often think of sleep as a process that the body needs to restore the brain , that is, that the memories are processed, and the cells are cleansed of toxins and prepared for a new day. At the same time, one of the biggest problems in the study of sleep is the definition of the concept of “dream”. Half of experts believe that any living organism is in this state in accordance with its biological clock , the rest are sure that sleep is peculiar only to people and other mammals . In a word, disputes are being waged around the border between a full-fledged dream and a simple rest.

Once and for all deal with the major controversial moments decided the team of scientists from the three laboratories at Caltech (Caltech), led by Lea Goentoro ( Lea Goentoro ). The object of their research was a rather unusual creature – meduzakassiopeya ( Cassiopea ). This marine creature does not move in the water column like most other jellyfish, but prefers to lie on the bottom in an inverted form, that is, tentacles up. At the same time, she constantly pulsates, like her free-floating relatives.

So, in order to be considered as a truly “sleeping” organism, one must demonstrate three characteristic features of behavior – a clearly expressed period of limited activity or rest, a reduced response to external stimuli during this period of time, and also suffer from lack of sleep, that is, show increased craving for sleep, if the day before failed, how to sleep properly.

As for jellyfish, the presence of all these features can easily be estimated from the rate of contraction. For this purpose, the animals were kept in aquariums with artificial sea water under the vigilant control of the video camera system.


It turned out that, like humans, jellyfish at night reduced their activity from 54 to 39 pulsations per minute. To test the reaction to stimuli, the Cassiopaea was placed on a platform suspended in the water column, which was pulled out as soon as the animal reached a state of rest, or rather, supposed sleep. In the control experiment with the wakeful jellyfish, she immediately rushed to the bottom, while the awakened Cassiopeia tried to understand for another five seconds what had happened.

Finally, the researchers had to stop the jellyfish from getting enough sleep . Achieving this was not difficult: it was enough every 10 seconds for 20 minutes “deep night” to shake the water in the aquarium. The next day, the exhausted animals demonstrated the classical behavior of a sleepy person, that is, they haphazardly slowed down their movements at an unusual time.

It turns out that such primitive creatures as jellyfish also need sleep, even without brains and possessing a fairly simple arranged nervous system. Nevertheless, the results of the research are unique, since they first show the antiquity of this type of behavior.

“Perhaps it does not sound surprising that jellyfish can sleep, because mammals are asleep, and some invertebrates, like worms and fruit flies,” says study co-author Ravi Nath. “But jellyfish are some of the most evolutionarily ancient animals, who slept at the dawn of the development of biological diversity. “

Undeniable evidence that the jellyfish is really asleep was received, but for the authors of the study this fact caused a whole series of new questions. Now they have to find out whether neurons are needed at all, so that the animal can sleep and what genetic mechanisms underlie this type of behavior. In addition, even more primitive creatures, such as sponges and even protozoa, have come under scrutiny.