A new study from Bar-Ilan University has traced one of sleep’s main functions back to some of the earliest animals with nervous systems, such as jellyfish and sea anemones. The research indicates that protecting neurons from DNA damage and cellular stress is a basic role of sleep that began long before the evolution of complex brains.
The study was conducted by teams led by Professor Lior Appelbaum and Professor Oren Levy at Bar-Ilan University. Previous work from Appelbaum’s laboratory had shown in zebrafish that neurons collect DNA damage during periods of wakefulness and need sleep to recover. This highlighted reducing DNA damage as a core reason for sleep. Neurons are especially vulnerable because they do not divide and are highly active cells.
Published in Nature Communications, the new research involved Dr. Raphael Aguillon, Dr. Amir Harduf, and others analyzing sleep in two ancient animal groups: diurnal jellyfish, which sleep at night and nap briefly at midday, and crepuscular sea anemones, which rest from dawn through the first half of the day. Using infrared video tracking and behavioral analysis, the researchers found both species slept about eight hours daily—similar to humans—and experienced increased DNA damage in neurons during wakefulness that decreased during sleep.
When these animals were kept awake longer than usual, their neuronal DNA damage increased. They then slept more afterward—a response called “sleep rebound”—which allowed them to recover and reduce DNA damage levels. Exposing the animals to UV radiation or chemicals that harm DNA also triggered recovery sleep in both species. Conversely, when melatonin was used to promote sleep, neuronal DNA damage decreased.
The researchers observed differences in how each species regulates sleep: jellyfish rely mainly on light-dark cycles while sea anemones depend more on their internal circadian clock. Despite this difference, both require sleep for neural maintenance.
Professor Appelbaum stated: "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." He added: "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."
The study also notes implications for human health since poor-quality sleep is linked with cognitive decline and greater risk for neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease—conditions possibly involving ongoing accumulation of neuronal DNA damage.
"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," concluded Prof. Appelbaum.
