Rosa O’Hara is a staff writer at Noema Magazine. She previously worked as a reporter in Indonesia.
Before biologist Daniel Martínez got married and had kids, he had an unusual, interim family. For more than four years, he hand-fed over 60 small, amoeba-like animals he called “worms.” They’d come from a tidal estuary in Long Island Sound in New York, and Martínez had gone hunting for them because he’d heard they may hold the key to everlasting life.
The animals were Hydra vulgaris, tiny marine organisms about a quarter of an inch long that cling to rocks and vegetation and other surfaces underwater. They look like plants but are carnivorous animals — technically a freshwater polyp (in the same biological class as corals), with spindly arms and a simple nervous system. They feed mostly on water fleas and other tiny crustaceans.
Martínez had heard a rumor that these peculiar creatures were, in fact, immortal. “I thought that that was bullshit,” he told me recently. But in the time he monitored the ones he gathered from the estuary, he noticed no signs of aging. He kept them in separate tanks, made sure to remove new ones that appeared (hydra can reproduce asexually and he wanted to make sure he tracked only the original ones), and three times a week he fed them a steady diet of tiny shrimp similar to what they would’ve eaten in the wild. When he moved across the country, he tucked them safely into a cooler in the back of a U-Haul and took them along with him.
The article Martínez eventually published about the hydra in 1998 noted their apparent lack of aging and caused a stir in the part of the scientific community that was interested in aging and longevity. Broadly speaking, most biologists agree that an animal’s lifespan is usually correlated to its size — the bigger you are, the longer you live. Most of the animals that live the longest are large, like elephants, whales and some sharks. Even other long-lived creatures like quahog clams are huge compared to the hydra, which never grow larger than a small fingernail. But Martínez concluded that they showed none of the usual signs of getting older, and that as long as they avoided being eaten by predators or poisoned with toxins, it was possible they may be able to live indefinitely.
There are a handful of other organisms — Turritopsis dohrnii, a jellyfish; planarians, a type of flatworm; even some turtles — that appear to have “biological immortality,” where the rate of mortality is not linked to chronological age, or that do not experience physical deterioration from age (senescence). These creatures still die and can be killed, but in some cases it appears possible that under the right conditions they could carry on living forever.
Scientists have been intrigued by animals that lack senescence for a long time. The experimental zoologist Abraham Trembley first studied the hydra nearly 300 years ago, cutting one in half in an effort to figure out whether it was an animal or a plant. He incorrectly hypothesized that if it survived and regenerated itself, it had to be a plant. Not only did it live, both halves grew into fully functioning hydras.
Pretty much since humans were first able to conceive of the limits to their time alive, they’ve searched for the secrets of immortality. The quest to live longer has animated many scientific endeavors and field research, some more sensible than others, and today continues to preoccupy many in the tech world who seek the vast profits that potentially await. Many look to the natural world for inspiration or models that humans might emulate in order to avoid the usual consequences of the progression of time. Though humans do now live longer on average than ever before (mostly as a result of improved standards of living, inoculation against disease and better sanitation practices), no breakthroughs in the quest to defeat aging have yet been made.
Thousands of years ago, the search for immortality was all about elixirs. Tales of sacred liquids or concoctions that would prolong the life of the drinker are threaded through myths from ancient civilizations like the Mesopotamians, Greeks, Japanese and Chinese. In the Gospel of John, Jesus is recorded as saying “Whoever drinks the water I give him will never thirst. Indeed, the water I give him will become in him a fountain of water springing up to eternal life.”
The quest for immortality-giving drinks sometimes took dark and odd turns. The 15th-century Pope Innocent VIII, for example, allegedly drank the blood of children, and Diane de Poitiers, the mistress and advisor to the 16th-century King of France Henry II, drank liquid gold in an effort to keep her youthful looks. She eventually died of chronic gold poisoning.
More recent scientists still looked to the nonhuman world for potential lessons in extending human life, especially species that seem not to age. August Weismann, born in 1834 and a pen pal of Charles Darwin’s, tried to determine what senescence really was — what happens biologically, in other words, when we age. Weismann wanted to understand the evolutionary reason for why things die. He came up with the idea of “programmed death”: The degradation of an individual is necessary for the success of the species. Building on Darwin’s ideas about evolution, Weismann figured that humans and other animals had evolved a “death mechanism” in order to create space for younger, fitter members of the species to thrive and procreate. Species-level evolution, he concluded somewhat counterintuitively, seemed to prioritize the death of individuals.
At the time, scientists thought that what was known as the Gompertz law of mortality, a simple formula that shows how a person’s likelihood of death increases with age, applied to all animals. The likelihood of death increases exponentially, according to the law, until it reaches its maximum — for humans, about 120 years. But some creatures, it would turn out, failed to obey.
In the 1970s, Jennifer Jarvis of the University of Cape Town was studying one of the oddest creatures on a continent full of unique life. As its name suggests, the naked mole rat is almost entirely bare of fur or hair, pink, round and wrinkled. They have impressive buck teeth that they use to tunnel underground, where they live in colonies of some 70 or so individuals.
Jarvis gathered multiple mole rats from the wild and attempted to breed them in her lab. She discovered that they engage in what’s known as “reproductive altruism,” in which some members of the species don’t attempt to reproduce, instead acting as workers for the good of the colony. Naked mole rats are part of a very small collection of mammals that operate a eusocial structure, where — like bees and termites — there is one queen, a few sexually active males and the rest of the colony are workers or soldiers. Eusocial animals cooperate to care for their young, and responsibilities are divided among the adults, who become permanently specialized for their role and often lose capabilities characteristic of the other labor divisions.
As time passes, a mole rat barely seems to age, strangely enough. They can live for about 30 years or more — far longer than any other rodent. (Most mice live for about a year, sometimes longer.) Scientists attribute this to their ability to significantly reduce their metabolism, their unusually active and efficient DNA repair abilities and also their protective natural environment — there are not many predators in their underground tunnels in East Africa. The oldest naked mole alive today is currently pushing 40.
DNA is crucial to aging — and not. When it gets damaged by, say, prolonged exposure to the sun, cells don’t function the way they should. The naked mole rat is especially good at repairing its DNA before this damage can be fatal. In humans, studies have shown that regular exercise may increase the body’s ability to reverse DNA damage, and an increase in physical activity lowers the risk of cancer.
Other animals similarly don’t seem to become likelier to die as they age. The oldest ocean quahog was named “Ming” after the Chinese dynasty — 1368 to 1644 — during which it was probably born. Ming was killed by researchers attempting to find out how old it was; counting the bands in a cross-section of its shell determined it to be 507 years old. Scientists think quahogs live so long because they are especially adept at folding proteins. Proteins build cells, and all kinds of issues — allergies, degenerative diseases — can occur if for some reason they become folded incorrectly and can no longer function optimally.
A couple of months ago, a team led by scientists at the Universidad de Oviedo published a study on the T. dohrnii — sometimes called the immortal jellyfish and one of the most unique animals in the game of defying mortality. Not only does the T. dohrnii not seem to age, it appears to “age backwards”: It moves from its mature to its juvenile phase and back again. In their study, the scientists tentatively concluded that its remarkable ability might result from having two sets of genes that act on DNA to repair and protect it. Humans only have one. But advanced biotech companies are developing drugs and other treatments, including CRISPR-based technologies, that target our DNA repair functions, especially in malignant tumors.
Daniel Martínez eventually tired of feeding his tiny hydra and changing their water every few hours day after day and year after year. He eventually killed the ones he had been studying, but other scientists conducted interesting research of their own . Thomas Bosch, a zoologist at the University of Kiel in Germany, learned that hydra are almost entirely stem cells. Stem cells are the “builders” of other cells, which most of the time then go on to serve a particular function but are unable to build more of themselves. Hydra stem cells, however, just make more stem cells, which means they have an unlimited ability to continuously renew. Unlike humans, whose bodies usually scar over injured areas, hydras devote a large part of their energy to regeneration. Cut off one of its limbs — or even its head! — and it will reorganize itself and regenerate.
Other animals have a similar ability to regenerate. The axolotl, a type of salamander, famously can regrow its tail, organs, limbs and spine if it needs to. Like the hydra, it uses stem cells to regrow body parts. Back in 2018, its genome became the largest to ever be sequenced. But it is so complex — 10 times the size of a human’s — that nailing down what genes give it regeneration abilities is particularly hard.
The secret to regeneration — “the billion-dollar question,” as Rob Steele, another hydra expert, told me — so far eludes scientists, just like immorality. Humans initially have a capability to regenerate fingertips as babies and young children, and our skin and liver are able to regenerate themselves at least partially.
This year, scientists managed to regenerate the legs of live adult frogs. They “weren’t perfect cosmetically,” a co-author of the study told NBC, “but they were pretty darn good legs.”
In Douglas Adams’s “Life, the Universe and Everything,” there is an immortal character named Bowerick Wowbagger the Infinitely Prolonged who initially enjoyed all that his endless years had to offer: “living dangerously, taking risks, cleaning up on high-yield long-term investments, and just generally outliving the hell out of everybody.” But eventually, the experience soured because of Sunday afternoons when he had run out of activities and a feeling of intense listlessness set in: “the long dark teatime of the soul,” Adams called it.
Perhaps an intense sadness would eventually creep into any human experience without end, and perhaps the finiteness to life is what gives it and our experiences its value. You can only read so many books, only travel to so many places, only spend so much time with friends and family. And it might be better to just enjoy the (finite) ride.
Daniel Martínez, whose insights into longevity are grounded in over two decades of scientific study, seems to reject the benefits of immortality entirely. When I interviewed him, he had just finished a long lunch with a friend and was about to go to Europe on vacation. “My recommendation to you is drink heavily and enjoy your life,” he laughed. “Sorry. Don’t quote that.”