New research confirms that even the simplest creatures sleep, suggesting sleep evolved long before complex brains. A study published in Nature Communications reveals that jellyfish and sea anemones enter a sleeplike state for hours each day, mirroring human sleep patterns. The findings challenge long-held assumptions about sleep’s necessity for advanced cognition.
Sleep in Brainless Creatures: A Biological Mystery Solved?
For years, scientists debated why animals sleep. This study suggests sleep is not tied to intelligence but rather to fundamental biological maintenance. Jellyfish and sea anemones, lacking a central nervous system, still exhibit periods of reduced activity and metabolic slowdown. Researchers induced neuronal damage in the creatures and observed a direct correlation : more damage meant longer sleep duration.
This reinforces the idea that sleep is a conserved function across evolution. From humans with intricate brains to jellyfish with simple nerve networks, sleep serves as a “window” for internal repair—fixing DNA damage and sustaining neuronal health.
Evolutionary Implications
The study supports the theory that sleep evolved before brains, making it a fundamental survival mechanism. It also highlights that the need for sleep isn’t dependent on intelligence; even organisms with no central nervous system need rest to function.
According to Philippe Mourrain, a sleep researcher at Stanford University (who was not involved in the study), this discovery confirms that sleep allows key housekeeping tasks to occur in all species.
Why It Matters
The simplicity of sleep in these creatures raises intriguing questions. If sleep is this basic, what drives it? The study suggests that cellular damage may be a primary trigger, but further research is needed. This could explain why humans also fall asleep when stressed or sick.
The fact that jellyfish and sea anemones sleep for up to eight hours per day—often at night—suggests that sleep may be tied to environmental rhythms, even in brainless organisms. The study proves that sleep is not a luxury of intelligence but a core biological process.
