The Turritopsis dohrnii jellyfish doesn’t die a natural death after it ages, but instead perpetually returns to infancy. Here’s what scientists are hoping to learn from it.

We all age in one direction in life. We enter into it as newborns—soft, cute, and helpless little creatures—and leave it at an advanced age (hopefully), usually equally helpless and perhaps cute, but certainly no longer soft. This is the cycle of life, and we’ve known it for a long time.

Yet, in nature there exists a species which, instead of galloping toward its third age, heads back to the beginning once it matures. And, unlike the tragic fictional character Benjamin Button, it doesn’t even die as a baby. On the contrary, once a baby, it grows up again, and the cycle repeats itself. This creature is the Turritopsis dohrnii, more commonly known as the “immortal” jellyfish—an animal that has no brain, no heart, no bones, and no eyes, but does have the ability to never die from natural causes.

The process goes like this: the jellyfish eggs grow into small, free-swimming larvae called planula larvae; these morph into polyps, tiny anemones whose stalks attach to coral reefs; and polyps bud off into immature baby jellies, which mature into medusae, the familiar umbrella-shaped, tentacled creatures that pulse along the oceans and mate to spawn eggs. Push a medusa enough, though, and it can skip the fertilization and larval stages, changing straight into a polyp—like a butterfly reverting back to a caterpillar.

Many other species of jellyfish can pull off this reverse aging trick and return to the larval stage, but only once and rarely after sexual reproduction, according to Reuters. The immortal jellyfish is unique in its ability to do this a seemingly infinite number of times.

An illustration of the different life stages of the Turritopsis nutricola, from “Memorial pamphlet containing certain drawings of Medusae” by William K. Brooks, published in 1910. The immortal jellyfish was initially included in the species Turritopsis nutricola until it was recognized as a separate species, Turritopsis dohrnii.

In a paper published in Proceedings of the National Academy of Sciences in July 2022, scientists from the University of Oviedo in Spain, attempted to shed light on this astounding process by looking into the genes that control the unorthodox life cycle of the immortal jellyfish.

Having the coordinates of the jellyfish’s whereabouts from previous studies in hand, Maria Pascual Torner, a postdoctoral researcher in the department of biochemistry and molecular biology at the University of Oviedo and one of the study’s authors, dove into the waters of Santa Caterina, a Mediterranean resort town in southern Italy. She and her colleagues gathered polyps and placed them into an aquarium, and let them metamorphose into medusae for a few days. To investigate how the jellyfish respond to stress, they starved the medusae.

“The medusae shrank into little balls, generated polyps, and began remaking their adult bodies,” Pascual Torner tells Popular Mechanics. So that they could see which genes controlled this whole process and were actively being used to make proteins, the researcher froze jellyfish samples from each life stage in order to extract their messenger RNA (mRNA), a molecule that puts DNA instructions into action. They also compared those genes to a set of almost 1,000 genes related to aging and DNA repair—all of which exist in most species, ours included.

“The jellyfish had extra copies of certain genes, which shows that these might be important for the creatures’ survival,” says Pascual Torner. Interestingly, genes related to DNA storage came into play to help the medusae make their proteins; but once the medusae went back to their polyp form, the same genes were silenced, with their proteins hitting rock bottom in the blob-like stage prior to turning into a polyp.

Reversely, genes related to pluripotency, or a cell’s capacity to branch out into many different types of cells or tissues in the body, went the other way. They remained quiet during the medusa stage, woke to action when the adult animal went into its stressful self-destruction mode, and helped in building it back, then re-hibernated when the process came to an end.

It is a remarkably coordinated choreography of back and forth, and the genes that control it require further investigation. “We’re not thinking about the key gene of immortality or the formula for immortality,” says Pascual Torner. Instead, she and her team are more focused on illuminating the genes that are the most promising for regenerative therapy, which is the process of replacing or regenerating deteriorating human cells, tissues, or organs to bring the body back to a healthier state

Their research on these regenerative properties of the jellyfish could potentially and slowly—because “science is slow,” Pascual Torner stresses—help the human body better fight the degrading effects of aging and the neurodegenerative and cardiovascular disorders that often accompany old age. She believes immortality is just a pipe dream and will remain as such.

“Think about our body system, which needs to be in an equilibrium,” says Pascual Torner. Every single minute, cells that are not functioning right are programmed for death through a process called apoptosis. “If we wouldn’t have death in our organism, in our organs, we wouldn’t be able to live as a system,” she says. Even our brains need death to survive. “When we go from zero to three years old, our brain is constantly growing, old neurons are constantly dying when their neuronal pathways are not being used,” Pascual Torner says.

In this respect, it’s a cosmic irony that the disease of cancer actually entails “rebellious” cells striving for immortality, though at the expense of the whole system. “Cancer cells are not in equilibrium with the other cells. These cells go their own way, and at the end they die because they make the organism collapse,” Pascual Torner says.

Not even the immortal jellyfish is invincible to death, come to think of it. “It is mortal because it has predators; sea snails or sea worms can eat it, and viruses or parasites can kill it,” Pascual Torner says.

For now, the “fountain of youth,” the spring that turns old, tired bodies into young and fresh ones, will remain mythical. “There are no concrete solutions for the fountain of youth,” Peter Trontelj, an evolutionary biologist at the University of Ljubljana in Slovenia, tells Popular Mechanics. Trontelj coordinates GENEVOLCAV, a project charting the genetic code of the Proteus anguinus, or the Slovenian olm, a cave-dwelling amphibian also known for its longevity properties.

“This is approximately the level of how far we expect to reach with our first results on the Proteus genome,” Trontelj says. He believes Pascual Torner’s jellyfish study has a lot of potential for further discoveries, but the road ahead is long until anything is meaningfully translated to medicinal or other human use.

“There’s also not much novelty because the functional properties of the genes that were found in the immortal jellyfish have been known and expected, and rejuvenation still means that the adult has to reduce to a clump of tissue before a totally new organism can grow from it,” Trontelji says. “The whole procedure looks like some form of cloning.” He also confessed terror at the thought of having humans live even longer on an increasingly crowded planet. “May be good for space travel, though,” he says.

Systems need entries and exits, as Pascual Torner puts it—by this point, we’ve already established that. But what would happen if storage proteins were tampered with to stay active during the polyp stage? Would the jellyfish continue its Benjamin Button path, or would it be forced to move in one direction: ours, forward? This, alongside further studying candidate genes already known to be important in aging, is on the scientists’ future research agenda. But they can’t stress enough that the human body is made to enter life and exit it.

That said, there are mysteries—like that of human consciousness—whose totality cannot be reduced to chemical equations, Pascual Torner admits. But that’s a whole different chapter. Until we get there, if ever, we might still want to make how we age a bit more pleasant