Aging & Longevity

Pondering Whether Human Lifespan Has a Limit

The existence of extremely long-lived species like the immortal jellyfish suggests that aging is not inevitable, and researchers are betting we can circumvent natural limits to human lifespan with biological interventions.

By Bennett M. Sherman

Key Points:

  • The immortal jellyfish and the freshwater hydra do not seem to age, which suggests that aging is not inevitable and that we may be able to increase lifespan through biotechnology.
  • Researchers are developing compounds to target aging by ridding the body of inflammatory cells and mimicking low-calorie diets.
  • Generating such interventions against aging may extend average human lifespan in the future and help superagers live past 110.

The oldest person to ever live was a French woman named Jeanne Calment who lived to 122. Her daily habits included partaking in a glass of wine and smoking a cigarette after meals. She also ate about 2.5 pounds of chocolate each week. Perhaps the most interesting aspect of her story, though, is that no one else has lived past 120 since she died. Moreover, while the number of people who live past 100 increases every year, the number living past 110 is not.

“This suggests that maybe there’s a natural limit to human lifespan,” Dr. Venki Ramakrishnan, a biologist who won the 2009 Nobel Prize for chemistry and the author of Why We Die, told WIRED.

Even so, if such a limit exists, it would need to be imposed by biological evolution. This, however, does not seem to be the case.

“Evolution wants to make sure that your genes have the maximum likelihood of being passed on,” Dr. Ramakrishnan says. “It doesn’t care about how long you live.”

Taking Dr. Ramakrishnan’s statement into account may help explain why there seems to be a general correlation between the size of animals and how long they live. Generally speaking, larger animal species tend to have longer lifespans.

Accordingly, most mayflies live one to two days, while monarch butterflies can live for months. Much larger bowhead whales, on the other hand, live more than 200 years. Additionally, Greenland sharks can live more than 500 years.

“If you’re a smaller species, there’s no point spending a lot of resources maintaining and repairing the body, because the likelihood of being eaten or starved to death are high,” says Dr. Ramakrishnan. “Larger species, on the other hand, will have the advantage of more time finding mates and producing offspring.”

Exceptionally Long-Lived Species and Whether We Can Overcome Limitations to Lifespan

Oddly enough, a few species seem to be exempt from this trend. For example, the hydra, a small animal with 12 tentacles that dwells in freshwater, does not seem to age at all. The immortal jellyfish can even age backwards. According to Dr. Ramakrishnan, the existence of these species suggests that aging is not inevitable and that we may be able to overcome natural limits to lifespan if we alter our biology.

This is why research geared toward understanding the biological underpinnings of aging is such a hot field these days. For example, over the past decade, more than 300,000 science papers about aging have been published. Furthermore, billions of dollars have been channeled into over 700 longevity startups, including Altos Labs, Human Longevity, and Calico.

The spike in aging research is all centered around scientists’ attempts to tackle how to slow aging through the development of new techniques. Those under development include how to destroy dysfunctional cells that contribute to inflammation (senescent cells) and reprogramming cells to revert them to an earlier developmental state.

Researchers are also looking at compounds that can mimic the effects of a low-calorie diet, which some researchers recognize as the one of the most well-established ways to slow aging in rodents. One of these compounds is called rapamycin, first discovered in the soil of Easter Island by microbiologists due to its antifungal properties.

“Later they found out that it was also a potent antitumor and anti-inflammatory,” Dr. Ramakrishnan says. “It’s also immunosuppressant, so it can also make people prone to infection and slow down wound healing. We need to find that sweet spot between not having the side effects and having just the [anti-aging] benefits.”

Most longevity scientists are also familiar with research showing that young blood can rejuvenate old bodies, at least in mice. This discovery first arose when researchers surgically connected the circulatory systems of a young and old mouse — a technique called heterochronic parabiosis. It was observed that this procedure slowed the symptoms of aging and lengthened lifespan by about 10%. While scientists are still trying to identify which factors in young blood cause this effect, there are companies that have jumped the gun and started offering young plasma to billionaires.

A Healthy Diet, Exercise, and Sleep Works Better than Any Medicine on the Market

While we are waiting for new developments with aging interventions, there are still things we can do, according to Dr. Ramakrishnan. He adds that eating moderate meal portions, consuming a healthy diet, and getting enough sleep and exercise all work better than any medicine on the market. None of them have any side effects, and all of them are free.


Prolonged heterochronic parabiosis decreases biological age and promotes longevity in old mice. Nat Aging. 2023 Aug;3(8):917-918. doi: 10.1038/s43587-023-00452-8. PMID: 37500974.

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