Sleep evolved before brains did, study finds

Sleep Evolved Before Brains Did, Study Finds

  • Pillows
  • 941
Despite lacking a brain, Hydra vulgaris, shown above, still needs to sleep.

Despite lacking a brain, Hydra vulgaris, shown above, still needs to sleep.

(Image: © Taichi Q. Itoh, Kyushu University)

Our brains need sleep to work properly. But it turns out you don’t need a brain to sleep.

In a new study, researchers identified a sleep-like state in a tiny, freshwater animal called a hydra, which has a simple anatomy and lacks a brain.

“We now have strong evidence that animals must have acquired the need to sleep before acquiring a brain,” study lead author Taichi Q. Itoh, an assistant professor at Kyushu University in Japan, said in a statement.

The study, recently published in the journal Science Advances, has implications for our understanding of the reason the need for zzzs evolved.

Related: Why do we sleep?

Sleep is near universal in the animal kingdom, seen in humans and all mammals, as well as in insects and even roundworms. However, all these creatures have some form of central nervous system, or brain, and so scientists didn’t know whether the evolution of sleep preceded that of brains, or vice versa.

Jellyfish, a relative of hydras that also lack a brain, have also demonstrated sleeplike behavior, Live Science previously reported. But the new study adds to these findings by showing that hydras not only sleep but also respond to the same molecules that regulate sleep in humans and other advanced animals.

“Based on our findings and previous reports regarding jellyfish, we can say that sleep evolution is independent of brain evolution,” Itoh said.

For the study, the researchers used a video-recording system — essentially a “hydra cam” — to monitor the hydras’ movement and determine whether they had entered a sleeplike state, or a state of reduced movement that could be disrupted with a flashlight.

They found that hydras had cycles of active and sleep states that lasted about four hours each.

What’s more, disrupting the hydras’ sleep state, with vibrations or temperature changes, resulted in signs of sleep deprivation — for example, the hydras needed to sleep longer afterwards, and showed reduced cell growth.

The researchers also exposed the hydras to chemicals involved in sleep regulation in people, including melatonin and the neurotransmitter, or brain chemical called GABA. Exposure to both of these chemicals increased sleep activity in the hydras.

However, the chemical dopamine, which has a stimulating effect on many animals, instead promoted sleep in hydras. It seems that “while some sleep mechanisms appear to have been conserved, others may have switched function during evolution of the brain,” Itoh said.

The authors also found that when they deprived the hydras of their “shuteye,” there were changes in the expression of more than 200 genes, including some that are involved in sleep regulation in other animals.

Overall, “these experiments provide strong evidence that animals acquired sleep-related mechanisms before the evolutional development of the central nervous system and that many of these mechanisms were conserved as brains evolved,” Itoh said.

Originally published on Live Science.  

Read More


0 out of 5 stars(0 ratings)

Leave a Reply

Why Everyone Can’t Stop Talking About the Nectar Mattress

Why Everyone Can’t Stop Talking About The Nectar Mattress Posted By irjacoby on Jun 6, 2018 The secret is out and people can’t stop buzzing about how sweet sleep is on a Nectar mattress. From Allure magazine to Good Housekeeping to your friendly neighborhood mattress reviewer, these folks have seen the light — and the […]

Read more

Buffy Vs Brooklinen Comforter – We Compare the 2 Down Alternatives

Hi, thank you for taking a look at our video today. We’re going to be comparing Buffy vs Brooklinen comforter. So here at, we try to break down all the details to make it easy for you. The customer to decide what’s best in terms of bedding and sleep products. So let’s get into […]

Read more
Which came first, sleep or the brain?

Which Came First, Sleep or the Brain?

IMAGE: Hydra vulgaris is a tiny cnidarian with a simple anatomy. Collaborative research led by Kyushu University found that, despite lacking a central nervous system, hydras exhibit characteristics at a molecular... view more  Credit: Taichi Q. Itoh, Kyushu University Stay awake too long, and thinking straight can become extremely difficult. Thankfully, a few winks of sleep…

Read more

Share Great Content for Our Resource Section

About provides the latest news, information and expert articles related to sleep, sleep research, napping and better health and wellness. We welcome visitors to share useful resources for our Editorial Team.

Have a suggestion? Send us an email at:


Suggest Content