Today, longevity is an industry. Influencers sell you diets and supplements, academics write books and stake their reputations on one antiaging strategy or another, and American entrepreneur Bryan Johnson has turned an excessive supplement consumption, a strict diet, and other often dubious longevity interventions into a (social media) experiment.

However, as João Pedro de Magalhães writes in the Clarkesworld essay “What is the Retirement Age of a Jedi?” there is no proven way to slow aging in humans. Lifestyle matters and winning the genetic lottery is probably your best bet at the moment. That doesn’t mean we’re not slowly unraveling the ticking of nature’s clock. Various strategies can be used in lab animals, from tiny worms and fruit flies to mice, to stretch their lifespans. So far, those strategies have proven hard to translate to humans, and even then, we do not live in highly controlled lab settings.

Fiction, too, is no stranger to exploring the extremes of human longevity. One of the earliest works of science fiction, Mary Shelley’s Frankenstein; or, the Modern Prometheus, features a creature that (who?) not only came back (piecemeal . . . ) from the dead but seems impervious to age as well. Or consider the titular Dorian Gray in Oscar Wilde’s The Picture of Dorian Gray, who defied aging by delegating its ravages to a hidden portrait. Tales of a fountain of youth have circulated across cultures for millennia.

Yet, we need not rely merely on hyperbole or fiction to trick Father Time. Mother Nature always has a few tricks up her stunning, vine-embroidered sleeves. Let’s explore three strategies that allow some animals to chuckle at aging like it’s no big deal: rejuvenate, slow down, and regenerate.

Turritopsis dohrnii, or To Be Young Again

For our first antiaging trick, we need to take a dip in the Pacific Ocean. Actually, any ocean will do. The little jellyfish Turritopsis dohrnii (previously joined with the species T. nutricula, but after genetic tests, it was given its own berth in the web of life) has unobtrusively traveled in ships’ ballast tanks to silently make its home in oceans across the globe. Because this jellyfish is so small (not even hitting 0.2 inches in diameter) and generally innocuous, scientists only found out about their “invasion” after the fact.

The adorable little critter has one more ace in its tentacles, though. If I tell you that it’s also known as the immortal jellyfish, I’m sure you’ll see where I’m going. In a curious case of a real-life Benjamin Button, T. dohrnii can revert to a juvenile stage under harsh conditions, such as starvation, injury, or sudden temperature changes. No matter which stage the immortal jellyfish’s medusa phase (the tentacled, free-living form we think of when we think jellyfish) is in, it can pop back to the juvenile polyp phase through a process called transdifferentiation. If that sounds a bit like biological alchemy, it’s because it is.

Transdifferentiation is switching from one cell type to another without having to go through an intermediate stem cell stage that is not quite the transformation from lead to gold, but, perhaps more impressively, from muscle to nerve cell or adult to juvenile cell. T. dohrnii and T. nutricula are, so far, the only known adult animals that can do this. The full mechanism of jellyfish immortality is not yet fully known, but we do know that it involves several gene networks, some of which include genes with homologs (genes descended from a common ancestor) in mammals, including us, humans.

Rejuvenation notwithstanding, most immortal jellyfish likely never get to practice their aging-defying skills for the simple fact that T. dohrnii is not invulnerable. Fish eat it. Disease kills it. Its immortality is potential, not guaranteed.

For our next temporal trickster, we need to venture into colder waters.

Somniosus microcephalus, or Go Slow and Stay Cold

We travel to deep, dark Arctic waters in search of something that lurks there, something large that has mastered the art of slowing down.

The Greenland shark (Somniosus microcephalus) is one of the largest shark species, with individuals recorded at close to twenty-one feet. Considering its body size, it’s also the fish with the lowest known relative swim speed. Its diet is varied and includes various fish and seals, but we still don’t know how these slow giants manage to catch their agile prey. Some researchers suggest that the sharks sneak up on their prey as it is sleeping. So far, we don’t have any direct evidence of that.

Why is this shark so slow? Fish are ectothermic, which means that their metabolism, and thus activity, depend on the temperature of their environment. Since the Greenland shark prefers deep, cold waters (31 to 54°F), it has a very slow metabolism, which tends to correlate with a long lifespan.

And indeed, these sharks are the longest-lived vertebrates we know. Based on growth rates and radiocarbon dating of eye lenses, lifespan estimates settle around 400–500 years, give or take a century. They sexually mature around 150 years of age, and pregnancies last between 8 and 18 years! These numbers are guesses, of course. Our observations of these ancient, reclusive sharks are sparse.

In contrast to mammals, many fish (including sharks) grow indeterminately, which means they grow throughout their lives, even if the rate of growth might change. Add an extreme lifespan, and you’ll end up with an icy ocean giant like the Greenland shark.

But it’s not only the cold that allows the Arctic shark to live for centuries. To reveal more of their secrets, I must first introduce you to a rather gruesome observation: most adult Greenland sharks carry a small parasite embedded in their eyes’ cornea, dangling like a loose thread. Naturally, the combination of harsh environmental conditions, extreme age, and eye-eating parasites led scientists to propose that the Greenland shark’s vision is not exactly its finest feature. Yet, a recent study suggests that we may have underestimated the icy giants. Even sharks over a century old didn’t show any retinal degeneration, and, in part, this is thanks to a bunch of DNA-repair genes. These sharks also have several copies of genes that suppress inflammation and support the immune system (to prevent tumor formation, for example). Research has further found that the muscle metabolism of S. microcephalus doesn’t decline with age.

Even though they might have tricked Father Time, these wonderful sharks may not be a match for a warming climate. For now, we can only speculate about the effects, but since a slow metabolism is linked to longevity, we might expect these long-lived sharks to not live as long in warmer waters. Research into their metabolic enzymes backs this up: heat increased the enzymes’ (and thus metabolism’s) activity, and (possibly) the aging process. It makes me wonder (free story idea for an interested reader) whether the elves in fantasy worlds prefer cold environments. Perhaps they should.

For our third immortality act, we stay in the water. We’ll just add a little myth.

Hydra spp., or Regeneration Central

As the second of his twelve labors, the mythological hero Heracles (romanized as Hercules) was tasked to slay the Lernaean Hydra, a multiheaded snake raised by angry stepmom Hera with the specific intent to best our hero. Heracles, always eager to show off, chopped off the Hydra’s heads. Job well done. Only . . . the Hydra’s heads regenerated.

Beating the beast would take two. Calling on the help of his nephew Iolaus, Heracles set himself to the task once more. This time, however, Iolaus cauterized the necks after a swift head removal procedure. Ten more labors to go.

Then, in the eighteenth century, scientists actually found Hydra. Fortunately, it was a group of small hydrozoans, evolutionary cousins to jellyfish and anemones. Basically, a tiny (less than half an inch) tube with tentacles, Hydras were named after the mythical Hydra because these critters have a remarkable capacity to regenerate. Cut off their head, or any other body part, and they happily regrow. Outdoing even their mythical namesake, a removed Hydra head simply regrows an entire body. Eat your heart out, Wolverine.

Their regenerative capacity resulted in the claim that our cute hydrozoans are biologically immortal (in principle). In scientific parlance, they show negligible senescence—their risk of death doesn’t meaningfully increase with age. A key driver for their endless biological repair skills is the transcription factor FoxO. A transcription factor is a protein that binds to DNA and controls the expression of several genes. In this case, genes involved in cell differentiation, stem cell behavior, and longevity. As a lovely twist, variation in a related transcription factor in humans (FoxO3) is strongly associated with . . . extreme longevity. If you want to grow very old as a human, be a little like a Hydra.

Like the Greenland shark, Hydras also have a robust DNA repair system, which illustrates that these three strategies—rejuvenate, slow down, and regenerate—and the biological mechanisms underlying them are not mutually exclusive.

There’s more than one way to become (sort of) immortal.

Bonus: Heterocephalus glaber, or the Mammal in the Room

For our bonus longevity champ, we leave the water entirely and burrow into the dry grasslands of the Horn of Africa. There, in the soil of Ethiopia, Somalia, and Kenya, we find a mammal that is peculiar in many ways, including its surprisingly long lifespan.

The naked mole rat (Heterocephalus glaber) resembles a wrinkled pink sausage that has grown incisors and ambitions. As a rodent, it sits relatively near us in the web of life. Jellyfish, sharks, hydrozoans . . . All our temporal tricksters so far have been aquatic, and none of them are particularly close relatives. The naked mole rat is a warm-blooded (well, kind of, we’ll get to that in a second) mammal.

Like our immortal Hydras, the naked mole rat shows negligible senescence. A mouse of equivalent size is geriatric at three years and dead by five. A naked mole rat can live past thirty, in good health. This is especially true for queens. Our subterranean rodents are, after all, eusocial, living in colonies much like ants and bees, where a reproductive individual lives among many “nonbreeders.”

To dramatically outlive the lifespan estimate for a rodent of their size, naked mole rats deploy an arsenal of biological mechanisms. H. glaber is remarkably resistant to cancer. In part, this is thanks to great DNA repair (a common refrain at this point). But naked mole rats have another trick: they produce a molecule called “high molecular weight hyaluronan,” which prevents cells from crowding together and turning malignant. Mice that are engineered to produce the naked mole rat version of hyaluronan live longer.

The only cancer ever recorded in naked mole rats was found in two individuals that lived in a zoo. The problem? Probably oxygen. In zoos, naked mole rats are kept at ambient oxygen levels (around 21%), but in the wild, in their cramped, subterranean tunnels, naked mole rats live at half of that and less. That has also made them adept at flipping a metabolic switch to lower their metabolism (hello, Greenland shark) and prevent tissue damage. Our longevity rodents also produce more stable proteins, and they do so with fewer amino acid “spelling” errors. They also maintain a supple vascular system throughout their lives.

It almost feels as if naked mole rats looked at a list of antiaging strategies and decided, “all of the above, please.” Interestingly, many of these strategies could (theoretically, potentially) also (partially) work in humans.

Coda: On What Immortality Is Actually For

Human immortality, or something close to it, is a staple of science fiction. Whether it’s through cloning, longevity treatments, endless regeneration, or obscure immortality cocktails, many visions of humanity’s future include a certain control over the time nature has bequeathed each of us.

Yet another staple of science fiction is that nothing comes for free. TANSTAAFL. There Ain’t No Such Thing As A Free Lunch, author Robert Heinlein knew. Will a greatly extended human longevity leave us callous and cold? Riddled with memory problems? Stuck in an ossified, stratified society?

In his 1947 short story “The Immortal,” Jorge Luis Borges imagines what becomes of a man who drinks from the fountain of youth. The narrator, a Roman soldier named Marcus Flaminius Rufus, spends years searching for the City of the Immortals after hearing rumors of a secret river whose waters grant eternal life.

The city is an Escherian ruin; an architectural nightmare of dead-end staircases, inverted arches, and doors that open onto blank walls or sheer drops. Built by the immortals themselves, the city is an act of self-refutation, a monument to the absurdity of construction when time is infinite. Outside the city, in the caves of the surrounding plain, the immortals themselves crouch in the dirt, naked and silent, for they have forgotten language. Urgency and identity have evaporated. The immortals have become interchangeable.

Perhaps this is the unique challenge of human immortality. The immortal jellyfish does not brood on its second childhood. The Greenland shark does not yearn to create and achieve across its five centuries. The Hydra regrows its tentacles with neither relief nor philosophy. The naked mole rat queen does not reflect on her exceptional longevity from the comfort of her tunnel. They are immortal without the burden of knowing.

The longevity industry—the supplements, the plasma infusions—touts the biology without reckoning with Borges—it assumes that more time is simply better, that the life extended is life improved. But Borges’ immortals didn’t lack for time. They lacked stakes, purpose, and meaning. No sketchy intervention currently on the market addresses that particular problem.

To live longer, we first need a life worth living.