Longevity: The Immortal Jellyfish – and What It Tells Us About Aging

A tiny jellyfish can reverse its own life cycle when injured or starving, turning back into its younger self instead of dying of old age like everything else

Most animals develop in one direction. An egg becomes a juvenile, a juvenile becomes an adult, the adult ages, and at some point it dies. The sequence does not run in reverse. One small jellyfish is the most famous exception. Turritopsis dohrnii is a hydrozoan jellyfish about 4.5 millimetres across, roughly the size of a little fingernail. Under stress, when it is injured, starved, or subjected to adverse conditions, the adult medusa does not si…