Humans began sleeping as a way to partly help reduce DNA damage in nerve cells, scientists at Bar-Ilan University in Israel discovered while studying jellyfish and sea anemones.

Researchers reached this conclusion by observing restful behaviors in the upside-down jellyfish Cassiopea andromeda and the starlet sea anemone Nematostella vectensis. The animals are known to have sleep patterns similar to humans, according to a study published in Nature Communications on Jan. 6."These results demonstrate that DNA damage accumulates during wakefulness and decreases during sleep," the researchers added. "Furthermore, these findings suggest that decreasing DNA damage during sleep is an evolutionarily conserved cellular function that may have contributed to the emergence of sleep in early metazoans."

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Both species sleep for about one-third of the day, irrespective of the timing of daily sleep. Melatonin also promoted sleep in the animals and scientists observed them sleeping at night and taking midday naps.

Though neither species has a brain, they do have neurons and react to light and when presented with food. The animals were observed sleeping in a dark-light environment and awake during the day.

How could scientists determine when the animals were asleep?

To determine when the animals were asleep, researchers measured their pulsation rates. To do that, an infrared camera was used to track the simultaneous behavior of multiple jellyfish during the day and night. The motions were recorded by monitoring the changes in pixel intensity.

Researchers found that when jellyfish pulsed fewer than 37 times per minute for more than 3 minutes, they responded more slowly to stimuli. Based on the biometric data, they used the pulsation rate as an indicator of when the animals were asleep.

What happened when the animals were sleep-deprived?

Sleep deprivation, ultraviolet radiation and mutagens increased neuronal DNA damage and sleep pressure, the study notes. Scientists later found that the sleep-deprived animals slept more than those that had not been sleep-deprived.

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However, spontaneous and induced sleep promoted genome stability, suggesting that the evolution of sleep may have occurred to repair DNA damage and reduce cellular stress in simple nerve nets.

Researchers discovered that the light/dark cycle and the need to maintain stable conditions regulate sleep in jellyfish, whereas the circadian clock and internal timings primarily regulate sleep in sea anemones.

“We suggest that sleep may have evolved to enable consolidated periods of neural maintenance,” the researchers wrote.

Michelle Del Rey is a trending news reporter at USA TODAY. Reach her at mdelrey@usatoday.com

This article originally appeared on USA TODAY: Jellyfish and humans may have one thing in common, new study says