✦ The Spark
One species of jellyfish can reverse its ageing process and return to being a baby — potentially living forever.
The Story
Turritopsis dohrnii, a tiny jellyfish about 4.5 mm wide, can do something no other animal on Earth can: when it gets old, sick, or injured, it can revert entirely to its juvenile polyp stage. This process, called transdifferentiation, turns already-specialised cells back into unspecialised ones — like hitting a biological rewind button.
In normal animal biology, cells differentiate into specific types — a muscle cell becomes a muscle cell and stays that way forever. Turritopsis dohrnii breaks this rule. Its cells can transform into completely different cell types, effectively rebuilding the creature from scratch. In theory, it could repeat this cycle indefinitely.
Scientists are intensely interested in this mechanism because transdifferentiation could unlock breakthroughs in regenerative medicine. Understanding how these jellyfish reprogram their own cells might one day help us repair damaged human organs or even understand the biology of ageing itself.
Make Your Prediction
What does Turritopsis dohrnii do when it gets old or injured?
Pick your answer to reveal the explanation.
Today's Challenge
Research one other animal famous for regeneration — like an axolotl (regrows limbs) or a planarian flatworm (regrows its entire head). Write three sentences about how its regeneration is similar to and different from the immortal jellyfish.
Talk About It
If humans could reverse their ageing whenever they wanted, do you think most people would choose to? What problems might that cause?
Is a jellyfish that keeps reverting to a baby and growing up again the same individual, or a new creature each time?
What would a world look like if nothing ever died of old age?
Go Deeper
The jellyfish doesn't escape all death — it can still be eaten, get sick, or be killed. "Immortal" refers only to its escape from biological ageing. Wild populations are thought to cycle through the reversion process whenever conditions become stressful.
Big Debate
If scientists developed a pill that let humans live forever (but still age), should it be free for everyone or would it be okay for only rich people to afford it? What would happen to the world?