Anyone who has ever looked in the mirror and tried to smooth their wrinkles away might well be jealous of the turritopsis dohrnii. The tiny jellyfish has the ability to regenerate its cells and literally turn back to a more youthful version of itself.
The turritopsis dohrnii is likely unique in this particular talent. But humans’ pursuit of immortality has prompted researchers to study creatures like jellyfish, lobsters, and the infamous hydra in order to better understand what biological means an organism might need to live forever—or, at least, a very long time.
The scientists who study these organisms don’t refer to their specimens as immortal; it’s a decidedly unscientific word. Instead, they study longevity. Regardless, their research inevitably raises philosophical questions about the true nature of immortality. If a being is truly immortal, should it need to eat to survive? Can an immortal being be killed?
These kinds of considerations matter when we’re trying to figure out what our goals are when it comes to life extension for humans. Do we want to make our bodies hardier and more resistant to diseases related to aging? Or do we want to be able to replenish our cells with completely fresh versions? Or, to put it another way—would we rather be more like the lobster, or more of a jellyfish?
What is aging?
Biologists call the act of aging “senescence,” which refers to how organisms break down as a result of living for extended periods of time. Senescence could result from the build-up of certain kinds of biological waste in cells, which can cause diseases like dementia, or from damage to certain tissues, in the case of heart disease.
Despite widespread interest in modern medicine for prolonging life by preventing and curing disease, there is still much work to be done in studying how to guard against these base biological breakdowns. Evolutionary biologists have found a tension between evolutionary theory and senescence. Animals that can live longer have a greater opportunity to procreate, which means evolution is at odds with aging and should favor longer-living organisms. But older organisms are typically weaker and more prone to genetic mutations that disadvantage the offspring, meaning genetic advantages might be squandered on evolutionary dead ends.
Consider the jellyfish
That’s why the case of turritopsis dohrnii is so extraordinary. The organism’s long life can be attributed to its ability to turn itself back into a mass of stem cells (called transdifferentiation) once it reaches the end of its adult life, and then emerge from that blob as a young polyp, fresh and eager to take on the sea yet again. It can even initiate this cycle when it’s physically injured, or to prevent itself from starving to death if it can’t find enough food.
Essentially, the only way this jellyfish dies is if some outside force kills it. It’s still subject to the aging process; it just ignores the dying part and returns to its juvenile state.
“It is just as if a butterfly de-differentiates [its] own cells and re-differentiates them into caterpillar cells, becoming a caterpillar. It is not an asexual reproduction, it is a backwards metamorphosis,” Ferdinando Boero, a marine researcher at the University of Salento, said in 2015.
But even though the jellyfish can Benjamin Button itself back from the brink of death, it’s still not immortal, according to Boero. “Now, the question of immortality is the trick. It is not immortal. If you press it under your thumb, it dies,” he said.
The jellyfish’s unique ability to start over as a juvenile is possible because it’s a simple creature. It’s only 4.5mm large, smaller than a fingernail, and doesn’t have a rigid form. More complex creatures, like the lobster, start to take on different natural processes to guard against death.
The mighty lobster
Stories regularly circulate on social media declaring lobsters’ immortality. While the crustaceans can’t actually live forever, they do have two biological advantages that make them relevant to longevity research.
First, lobsters grow indeterminately, meaning that they grow until their environments can’t support their growth anymore. In the ocean, the limiting factor is typically the amount of nutrients that the lobster can find. A set amount of crabs, mussels, and clams to munch down on means a set amount of growth.
The lobster also doesn’t seem to die from the diseases that affect many other organisms. For example, lobsters don’t get cancer, according to marine researcher and lobster expert Jeffrey Shields. He says that in more than a decade of research, he’s only seen three cases of tumors on lobsters pulled out of the ocean, and they’ve all been benign.
But lobsters obviously can die—in the ocean as well as in a pot of boiling water at your local seafood joint.
In the wild, lobsters are more likely to get shell diseases if they grow to a size where they cannot molt again because there are not enough nutrients in their environment to support the process. They can also die from infections after their shell has been damaged in a scuffle.
One natural way that lobsters can die is during molting, where they shed their shell to grow a larger one. If the lobster is too muscular to squeeze out of its old shell, it will die in the process of trying to escape the prison of its own carapace. This becomes more likely as they grow larger with time.
“Think of it as if we’re going to try and wriggle out of our pajamas, and if we don’t wriggle out of our pajamas, we die,” Shields said.
This is a form of physiological senesence, Shields says, as the lobster’s own body can’t support its growth anymore.
There’s still more research to be done on the lobster’s longevity. Since American lobsters can live about 30 years on average, there haven’t been many long-term trials documenting how lobsters die, according to Shields.
A healthy hydra is a happy hydra
The organism that comes closest to being truly immortal is the hydra. The hydra is a small freshwater polyp that looks like a small tube with a circular fan of appendages emerging from one end. Unlike the turritopsis dohrnii and the lobster, the hydra does not age.
Daniel Martinez, the researcher who first identified the hydra’s near-limitless lifespan, discovered it when a longevity experiment unexpectedly kept going for four years because very few of the hydra actually died—rare for a species that matures in a matter of days. The risk of a hydra dying as a result of aging is so low that the study concluded that if the experiment’s conditions continued, 5% of the original hydra would still be alive in 1,400 years.
Simpler organisms like the hydra, especially haploids (organisms that only have one set of chromosomes), might be the closest thing to classically immortal, according to Shields. Since there’s so little genetic material to work with compared to a more complex organism, haploids have evolved so that their DNA is more accurately replicated when dividing.
Larger organisms, meanwhile, are typically more complex. That means there are a lot more things that can potentially go wrong as their genetic code replenishes cells, potentially leading to uncontrollable genetic mutations like cancer.
Humans are undoubtedly complex. If you want further proof, watch an episode of The Bachelorette and realize that the social situation is both far too complicated to jump into mid-season, and beyond that, each contestant is the product of an endlessly complex evolutionary soup that has weighed their longevity against their ability to procreate, with the end result of appearing on a game show.
The burden of our human complexity—beyond more seasons of The Bachelor franchise—is that scientists’ continuing research on jellyfish, lobsters, and hydra are unlikely to result in miracle cures for us in the near future. These organisms are pilots for increasingly larger experiments that could one day include humans. But until then, we’ll always have Botox.