🌅 What Jellyfish Sleep Tells Us About Brain Evolution

SOURCE

Aguillon et al. (2025)

WHAT TO KNOW

• A new study by researchers at Bar-Ilan University in Israel found, despite lacking a centralized brain, jellyfish and sea anemones spend about one-third of the day sleeping, just like humans. Also like humans, the sea creatures need more rest after having a bad night’s sleep, and they experience similar sleep-inducing effects in response to melatonin, a hormone the human brain secretes at night to promote sleep.

WHY IT MATTERS

• The work suggests sleep may have evolved to help protect nerve cells from DNA damage associated with wakefulness, long before the cells became centralized in the brain. Since jellyfish and sea anemones are among the earliest creatures to develop nervous systems, the authors also believe the findings support the theory that protecting nerve cells from DNA damage and cellular stress is a basic, ancient function of sleep that began long before complex brains evolved.

CONNECT THE DOTS

• Sleep is one of science’s enduring mysteries. Despite being universal among animals with nervous systems, it also carries clear evolutionary risks, like leaving organisms vulnerable to predators and environmental hazards, and occupying time that could otherwise be spent eating or reproducing. In humans, sleep supports brain health by clearing out waste and preserving memory. Poor sleep is also associated with cognitive decline and an increased risk of neurodegenerative diseases, like Alzheimer’s and Parkinson’s.