Nature
One jellyfish can reverse its own aging and start life over as a baby again
When injured, sick, starving or old, Turritopsis dohrnii can revert its adult cells back into an earlier polyp stage, the biological equivalent of a butterfly turning back into a caterpillar, and grow up all over again. Marine biologists only realized this in the 1990s, decades after the species was first described. In principle the cycle could repeat indefinitely, though predation and disease still kill most individuals.