Is 115 about as good as it gets? (iStock)

All animals — with the exception, perhaps, of the seemingly immortal little sea creature known as the hydra — have a shelf life. They may live shorter or longer spans in captivity, in times of feast or famine, or in different habitats. But eventually, even with all the resources and coddling the world can possibly provide, a species will reach the limit of its natural life span. Even the most beloved, pampered pet pooch cannot live forever. According to a new study, humans are no exception to this rule.

And we may be reaching the upper limits of our potential time on Earth.

A study published Wednesday in Nature suggests that the natural human life span maxes out at about 115 years. Modern medicine and abundant resources for the elderly in developed countries have produced a wealth of centenarians, the study authors report, but the current record for the oldest living human — 122, the age of Jeanne Calment when she died, in 1997 — is unlikely to be broken more than incidentally.

“It is possible that someone might live slightly longer, but the odds of anybody in the world surviving to 125 in any given year is less than one in 10,000,” study author and molecular geneticist Brandon Milholland of Albert Einstein College of Medicine, in New York, told Reuters.

He and his colleagues came to this conclusion by analyzing decades of longevity data from about 40 countries. As just about anyone could tell you, it has become increasingly common for those in wealthy nations to live to ages that once would have seemed impossible. For decades, the ages of the oldest living people were increasing over time — but that slowed and pretty much stopped by the 1980s. And the researchers found that, based on statistical trends, those who reach age 110 today do not have a longer life expectancy than individuals who reached the same age decades ago.

The results may sound straightforward, but life span is a debated subject in the scientific community. Many researchers hope that by developing therapies that target the individual effects of aging, we could extend human lives much further than they last now. One expert disputed the results and told the New York Times that the new study was “a travesty.”

Others have slightly more nuanced criticism for the conclusions of the study: Tom Kirkwood of Newcastle University, a researcher who was not involved in the new research, thinks that interventions for specific kinds of age-related biological decay could still extend the human life span.

“There is no set program for aging and we know that the process, which is ultimately driven by the buildup of faults and damage in the cells and organs of the body, is to some degree malleable,” Kirkwood told the Guardian. “Even without any change in the biology of aging, it is almost inevitable that the current record will be broken.”

Just how those therapies might be developed — and just how successful they might be — remains to be seen. Some even say that such science-fiction-like follies are ethically dubious. More importantly, they may prove too difficult to implement. The authors of the new study argue that to significantly increase the human life span, one would have to use genetic engineering and pharmaceutical intervention to plug the ever-springing, ever-changing leaks in a crumbling dam.

Biomedical gerontologist Aubrey de Grey, who has famously argued that the first human to live to be 1,000 is already alive today, still sees age as nothing more than a disease to be cured — and a manageable one at that.

“Unlike a dam, the pressure on the so-far-unplugged leaks actually diminishes as one plugs more and more of them,” he told Nature. “The result in this paper is absolutely correct, but it says nothing about the potential of future medicine, only the performance of today’s and yesterday’s medicine.”

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