Is Any Animal Immortal? Jellyfish, Hydra, and Long-Lived Creatures

Stories about animals that never die have been popular for years. Most of them are exaggerated. But a few animals really do seem to escape the usual rules of aging, and scientists study them closely. This article sorts out what is known.

What does “biologically immortal” mean?

That an animal does not die of old age. It does not mean that it cannot die. The University of Florida’s iDigBio program notes that even the so-called immortal jellyfish usually dies in the wild from predators and other dangers. Being biologically immortal means only that aging itself does not set a limit on life.

What is the “immortal jellyfish”?

A tiny jellyfish called Turritopsis dohrnii. Curious, from the Australian Academy of Science, says it is the only species that has been called biologically immortal. When it is stressed, by starvation or injury, it can revert to the earliest stage of life, a tiny polyp, and start over. Scientists call this transdifferentiation. Curious notes that the jellyfish is not truly immortal. A fact-check by Africa Check cites the American Museum of Natural History and BBC Earth. It says that one, or possibly two, jellyfish species can be considered “immortal.” That does not mean they can always cheat death.

What about hydra?

Hydra are small freshwater animals related to jellyfish. Popular Science reports on a 1998 study of hydra that found no evidence of aging, concluding that hydra “may have indeed escaped senescence.” Curious says hydra do not seem to go through aging at all. They die, from disease, predators, or starvation, but not because of aging.

Are lobsters immortal?

No, though the myth is popular. Africa Check, citing Smithsonian Magazine, says lobsters have “indeterminate growth,” meaning they keep growing throughout life by shedding their shells. Each molt takes more energy than the one before, and lobsters do die. Curious explains that lobsters have an enzyme called telomerase that rebuilds the ends of chromosomes, which most human cells largely lose. But having the enzyme does not make an animal immortal.

How long can an animal live?

Very long, in some cases. Popular Science reports a 2016 study that dated the eye lenses of 28 female Greenland sharks and found that the oldest was about 400 years old, and possibly more than 500. The sharks do not seem to reach reproductive age until about 150 years. These animals live extremely long lives, but they do age and die.

What can we learn from them?

Clues about how aging works. Popular Science notes that what happens in hydra and in the jellyfish could mean that many related species follow their own rules of aging and regeneration. Scientists hope to learn from them, though what works for a jellyfish may not work for a human. For why aging evolved, see Why Do We Age and Die?, and for human longevity, Can Humans Live Forever?.