Protective Origins of Sleep

Recent experiments show sleep‑like states in Cnidaria (jellyfish and sea anemones) and support the hypothesis that sleep originally evolved not as a brain luxury but as a protective, restorative state for excitable tissues long before complex brains emerged. If sleep’s ancestral function is cellular protection from daily metabolic or oxidative stress, that reorients research toward conserved repair mechanisms across animals and new clinical targets for sleep‑linked disorders. — This reframes debates about sleep from behavioral/cultural framing to a deep evolutionary and biomedical question, with implications for sleep‑medicine priorities, ageing research, workplace regulation (shift work), and how we translate animal models to human health.