Well, that depends on how you think about immortality or living forever.
The animal most discussed with this phenomenon is Turritopsis dohrnii sometimes called the immortal jellyfish. What makes this jellyfish so unique is that it can basically reverse its aging. Almost like a real-life Benjamin Button, but not so slowly. Instead, it reverts from the adult capable of swimming about and eating prey, to the sexually immature polyp stage.
The typical lifecycle goes like this: a larval stage, called planulae, formed from the fertilized egg of an adult jellyfish swim around until they settle on some form of hard surface that will hopefully serve as a safe nursery for the next stage of life, the polyp stage. Many cloned jellyfish bud off and become the form most often associated with jellyfish, the medusa. Capable of sexual reproduction these adult jellies then can create eggs and sperm that can join together and continue the cycle anew.
But this jellyfish has a unique cellular ‘superpower’. If damaged, starving, or living conditions become too harsh for the delicate adult, its cells can undergo transdifferentiation or the turning of cells from one type into another one entirely. In doing so, it reverts back to the polyp stage. Settling back down on the seafloor ready to clone biological material again, and make more jellyfish. Remarkably, given the proper conditions, they seem capable of doing this without end in experimental labs.
Now, the reality here is that nothing about transdifferentiation gives them any sort of protection against many of the dangerous threats of living in the ocean. Simple predation could end their lives and render them completely incapable of continuing their immortal existence. Plus, eternity is a long time, our experiments only go so far in testing the ‘lifespan’ of a creature, who knows what thousands of identical biological replications would do to an organism. We simply don’t know; we haven’t even observed the process in the wild due to the precise conditions and narrow window of opportunity to do so.
Another aspect of immortality to consider comes from the ancient philosopher Plutarch: The Ship of Theseus. The simple version of the puzzle is asking if a ship is docked, and every board, nail, and sail is replaced with a new piece, is it still the same ship? While we may leave the philosophical debate up for another article, it is an important consideration when it comes to the “immortality” of this jellyfish. As new cells are made from the prey consumed by the jelly in its adult form, and existing cells are spread out amongst the clones budding off from the polyp stage, cells are constantly being replaced. At what point is every cell replaced and the organism considered a different specimen? I’m not sure science is adequately prepared to give an answer to that question yet. At least not one that will satisfy everyone.
Is there a future for humans using this transdifferentiation? We are currently already studying a similar cell type transformation in human stem cells called metaplasia. These cells are of particular interest to researchers for testing drug effects and even regrowing organ tissue. But, if there is a secret to reversing aging and somehow achieving life capable of not dying from old age, clues may exist in the tiny jellyfish living at the bottom of the sea.
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