Study suggests sleep's core role in repairing DNA damage preserved across animal kingdom

The evolutionary drive to maintain neurons that we see in jellyfish and sea anemones is perhaps one of the reasons why sleep is essential for humans today, Appelbaum said.

A new study that looked at sleep patterns in jellyfish and sea anemones found that sleep helps reduce DNA damage, indicating how the core functions of sleep may have emerged millions of years ago in some of the earliest creatures with nervous systems.

Sleep is known to be critical for optimal biological functioning. However, among animals, sleep poses survival risks as it diminishes an individual's awareness of the environment, leaving one more exposed to predators, researchers from Israel's Bar-Ilan University said.

Despite the risks, sleep is an evolutionarily conserved process vital for animal survival and has therefore been one of biology's enduring enigmas, they said.

''Sleep may have originally evolved to provide a consolidated period for neural maintenance, a function so fundamental that it may have been preserved across the entire animal kingdom.

''Our findings suggest that the capacity of sleep to reduce neuronal DNA damage is an ancestral trait already present in one of the simplest animals with nervous systems,'' lead researcher Lior Appelbaum, from the faculty of life sciences at Bar-Ilan University, said.

The researchers studied sleep patterns in two ancient animal lineages: jellyfish, which sleep at night and take short nap at mid-day, and sea anemones, which sleep from dawn through the first half of the day.

Even though these creatures lack a brain, they do have a nervous system.

Using infrared video tracking and behavioural analysis, the team observed that the animals slept roughly eight hours a day -- similar to human sleep duration.

Despite their differences in lifestyles and mechanisms controlling sleep, the animals shared a pattern -- DNA damage was found to accumulate in neurons while the animals were awake and reduced during sleep.

The longer the animals were kept awake, the more the DNA damage and the longer they slept afterwards, a ''sleep rebound'' behaviour that enabled recovery.

The researchers also found that increasing DNA damage -- through ultraviolet radiation or exposure to a DNA-damaging chemical -- triggered sleep in the species studied.

However, promoting sleep with the hormone melatonin was shown to reduce DNA damage.

The findings reveal a bidirectional relationship in which DNA damage increases sleep need, and sleep, in turn, facilitates damage reduction, suggesting that protecting neurons from daily cellular stress and DNA damage may have been the evolutionary driver of sleep, the researchers said.

''Sleep is important not just for learning and memory, but also for keeping our neurons healthy. The evolutionary drive to maintain neurons that we see in jellyfish and sea anemones is perhaps one of the reasons why sleep is essential for humans today,'' Appelbaum said.

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