When I try to picture death and understand my life in relation to its ultimate, inevitable end, I always come up short. The impossibility of death in the mind of someone living—to borrow a phrase from Damien Hirst—brings us hard up against the limitations of imagination. Of course, I will die one day, whether I can conceive of it or not. And so will almost every living creature on this Earth.
But perhaps not quite all. Several species display remarkable feats of survival, withstanding extreme conditions for years on end. Tardigrades, for example, the millimetre-long micro-animals known as “water bears,” have been known to survive the radiation of space flight, and temperatures from up to 150C to absolute zero. Tardigrades have been kept for eight days in a vacuum, then in helium for three more, and still come back to life afterwards.
Brine shrimp—which you might know as “sea monkeys”—are similarly hardy; when desiccated, like tardigrades, they dry out and enter a state of suspended animation for years at a time. In the 1990s, an oil exploration crew drilling near Utah’s Great Salt Lake dredged up brine shrimp cysts (embryos) estimated to be 10,000 years old. When dropped in water, several hatched and began to swim.
But though the tough-it-out methods of the tardigrade and the brine shrimp—which slow their metabolism down to 0.01 per cent or less of their normal rate—are impressive enough, nothing compares to the regenerative abilities of the Turritopsis dohrnii, the so-called “immortal jellyfish.”
An eagle-eyed swimmer might come across this wispily ethereal creature in the warm and limpid waters of the Mediterranean, or the Caribbean, or the seas around Japan. It’s around the size of a fingernail and has the appearance of a glass noodle with a droplet of blood at its centre. It pulses through the water, its delicate, thread-like tentacles streaming out behind. But when the reaper calls—in the form of, say, a serious wound—it doesn’t simply die. Instead, it responds to stress by allowing its mature body and tentacles to deteriorate, and reverts to its previous form as a polyp—a small, stalked creature attached to the sea floor. Stunned scientists first observed this reversion in the early 1990s, describing the jellyfish’s regression to an earlier stage of life as being “like a butterfly transforming back into a caterpillar.” But only in recent years have the jellyfish’s full Benjamin Button-like capabilities been fully appreciated.
Japanese scientists have induced the jellyfish to repeat this transformation at least 10 times in a row—allowing a polyp to grow into a tentacled adult medusa, before subjecting it to stress (for example, a needle prick), and watching the process begin all over again. In this way, a single jellyfish—hypothetically at least—might be induced to live forever, cycling endlessly from young to old and back again.
As party tricks go, it’s an excellent one. But whether the immortal jellyfish is aware of the gambit is a different question. Jellyfish have no central brain, but they do have a central nervous centre with decision-making powers. A network of neurons links light sensors, and small finger-like structures—like our own inner ears—assist in their orientation. Box jellyfish, which are unusually complex, have 24 eyes apiece, and—though technically brainless—hunt and engage in mating rituals.
The immortal jellyfish has something that humans have sought for centuries: the answer to eternal life. But to them, it is nothing. Workaday. Simple creatures, they may not even know they have this prize. Certainly, what with their rejuvenation coming during periods of pain or suffocation, they will not enjoy it. Friedrich Nietzsche wrote: “One has to pay dearly for immortality; one has to die several times while one is still alive.” I’m sure that jellyfish would, if they could, agree.
