Sleep Evolved First Before the Brain, Study Finds

A victory for sleepyheads!
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People who love to sleep may have just found an ally in scientists, who discovered sleep may have come first before the brain. 

A new study published in Science Advances suggests animals may have evolved to sleep before they even had brains. The study focused on a species of a brainless animal called hydra in an attempt to understand the evolutionary origin of sleep.

A hydra is a type of freshwater organism closely related to the jellyfish. They are also known as freshwater polyps. It was named for its regenerative abilities, similar to the hydra in Greek mythology. The hydra animal is nearly immortal—they do not age nor die of old age. In fact, scientists believe hydras can live an estimated 1,400 years, and they don't have brains. 

But its biological immortality is hardly the reason why scientists decided to study it. They wanted to study the evolution of sleep in animals. 

"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.

Scientists wanted to understand why animals ever needed Zzzs. 

Apparently, some scientists around the world invested time and money figuring out why people aren't awake all the time, as if we aren't sleep-deprived enough. 

Sleep is a universal mechanism for all animals, brainless or not. It has been observed in all species, including the jellyfish, another brainless animal and relative of the hydra. 


"Many questions still remain regarding how sleep emerged in animals, but hydras provide an easy-to-handle creature for further investigating the detailed mechanisms producing sleep in brainless animals to help possibly one day answer these questions," said Itoh. 

For animals with brains, sleep is monitored through observation of brain activity. For hydras and other brainless animals, scientists had to observe their reduced movement. 

Jellyfish and hydras are among the oldest multicellular organisms on earth. Jellyfish are 500 million years old, while hydras are estimated to be 600 million years old—predating brains by a couple of million years. 

According to the journal Science Advance, researchers did various experiments on the hydra, including inducing sleep deprivation by disturbing its surroundings. They found that it caused changes in the expression of the hydra's 212 genes, including one that regulated sleep in many animals. 

Conclusion: Sleep Came First Before the Brain

The scientists involved in the study made a groundbreaking conclusion: Sleep is so important, such that nature decided to evolve it first before the brain.

But we already knew that. 

"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.

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