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Cracking Sleep's Evolutionary Code: Neuron Protection Traced Back to Jellyfish and Sea Anemones

Upside-down jellyfish sleep about 8 hours daily, reducing neuronal DNA damage and increasing sleep after disruption, suggesting sleep predates brains as a cell-protective behavior.

  • Bar‑Ilan University researchers found in Nature Communications that Cassiopea andromeda, upside-down jellyfish, sleeps roughly 8 hours daily, mostly at night with a short midday nap.
  • Mounting evidence that sleep predates brains led researchers to test simple animals because sleep is conserved across nervous systems and may have arisen in marine species as human ancestors diverged from Cnidaria around a billion years ago.
  • Using 24-hour tank recordings, the team observed Cassiopea andromeda pulsed more than 37 times per minute by day with faster responses, while night showed slower pulsing and ultraviolet light increased sleep pressure.
  • Analysis showed DNA damage builds during wakefulness, and sleep reduces it; melatonin and induced sleep lowered neuronal DNA damage, supporting genome stability, Appelbaum and colleagues report.
  • Further research is required to see if results extend to other jellyfish species and mammals, as the study first characterizes sea‑anemone sleep in Nematostella vectensis, with co-authors noting a likely core sleep function.
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Sleep in jellyfish and marine anemones breaks one of the most widespread ideas about rest: there is no need for a complex brain to sleep, but neurons that need protection from daily wear from being awake. This finding has revolutionized the scientific understanding about the origin and function of rest in the animal kingdom. Jellyfish and anemones lack a centralized brain; instead, they have distributed nerve networks. However, studies have obse…

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Lean Right

A new work on nettle animals suggests that sleep was born very early – with the aim of enabling coordinated maintenance of damaged nerve cells.

·Vienna, Austria
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Center

Marine jellyfish and anemones sleep about a third of the day, as do humans, with whom they share remarkable similarities in sleep patterns.A study published by Nature magazine, signed by researchers at Bar Ilan University (Israel), supports the hypothesis that sleep evolved into a wide range of species to reduce DNA damage, especially in brain neurons associated with waking state. Previously, a dream-like state had been documented in Cassiopea j…

·Madrid, Spain
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Nature broke the news in United Kingdom on Tuesday, January 6, 2026.
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