The Jellyfish That Can Reverse Its Own Aging

What happened?

The creature is Turritopsis dohrnii, a jellyfish no bigger than a pinky fingernail — about 4.5 millimeters across — that lives in temperate and tropical seas worldwide. Like most jellyfish, it starts life as a larva, settles into a colony of polyps anchored to the seafloor, and then buds off into the free-swimming, sexually mature medusa form we recognize as a “jellyfish.”

Here’s where it breaks the rules. When a typical jellyfish reaches the end of its adult life, it dies. But when Turritopsis dohrnii is starved, injured, or otherwise stressed, it can do something almost no other animal can: it reverses course. The adult medusa transforms its cells and reverts all the way back to the polyp stage — effectively returning to childhood — and then grows up all over again. This earned it the nickname “the immortal jellyfish.” Researchers documented the full life-cycle reversal in a landmark 1996 study, and the species was formally distinguished from its look-alike relatives in 2006.

Why was it strange?

Animals are supposed to develop in one direction. A tadpole becomes a frog; a frog does not become a tadpole. The cells in your body specialize early — a skin cell stays a skin cell — and that one-way street is what we usually mean by “growing up.” Turritopsis dohrnii drives the wrong way down that street through a process called transdifferentiation, in which already-specialized cells transform directly into entirely different cell types. It’s as if a butterfly could melt back into a caterpillar whenever life got hard.

“Biologically immortal” doesn’t mean invincible, though, and this is the part that often gets garbled. In the wild, the vast majority of these jellyfish still get eaten by predators or killed by disease long before they ever pull off the trick. Immortality here means no fixed expiration date — not an inability to die.

What did scientists learn?

The jellyfish has become a serious target for aging and regenerative-medicine research. In 2022, scientists sequenced its genome and compared it to a non-rejuvenating relative, identifying genes linked to DNA repair, stem-cell renewal, and the maintenance of telomeres — the protective caps on chromosomes that normally shorten as we age. Studying how this animal resets its own cellular clock could eventually inform research into human tissue repair, though scientists are careful to note that human “immortality” is not on the menu.

How does it affect us today?

Beyond the lab, Turritopsis dohrnii is quietly spreading across the world’s oceans, hitching rides in the ballast water of cargo ships — a “silent invasion,” as one Smithsonian researcher called it, that goes unnoticed because the animals are so tiny and harmless. For the rest of us, it’s a humbling reminder that some of biology’s most radical capabilities are hiding in animals we’d never look at twice.

Fun fact

Keeping these jellyfish alive in a lab is so difficult that for years essentially one scientist — Shin Kubota of Kyoto University — reliably managed it. Over a two-year span, his colony rebirthed itself 11 times. Kubota is also known for writing and singing songs about the immortal jellyfish on Japanese television.

Sources

• “Turritopsis dohrnii,” Wikipedia — https://en.wikipedia.org/wiki/Turritopsis_dohrnii
• S. Piraino et al., “Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula,” The Biological Bulletin, 1996
• Pascual-Torner et al., “Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation,” PNAS, 2022 — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9459311
• Nathaniel Rich, “Can a Jellyfish Unlock the Secret of Immortality?” The New York Times Magazine, Nov. 28, 2012