Immortal Jellyfish

The typical life of a jellyfish follows a one-way path from a larva to a stationary polyp, and finally to a free-swimming medusa. However, the tiny *Turritopsis dohrnii* defies this fundamental rule of life. When faced with environmental stress, physical harm, or even the effects of aging, this remarkable creature can halt and reverse its development. Instead of dying, the medusa's body collapses in on itself, reverting to a polyp, an earlier and sexually immature stage of its life cycle. From this new polyp colony, genetically identical jellyfish will eventually bud off, effectively restarting the life cycle.

This unique process of age reversal is known as transdifferentiation, where the mature, specialized cells of the jellyfish essentially transform into different cell types, reprogramming themselves to begin anew. This biological phenomenon was first observed by scientists in the 1990s, challenging the understanding that life progresses in only one direction. While this ability makes *Turritopsis dohrnii* biologically immortal, it doesn't mean it can't die. The jellyfish can still fall prey to predators or be killed by diseases, meaning its potential for an endless life is often cut short by the realities of its environment.