H

umans are living longer than ever before. But does our species have a fixed shelf life, or could we prolong our lives indefinitely?

A new study in Science suggests that we haven’t yet hit our limit on longevity — findings that come amid a heated debate on the question and that will almost surely be disputed by scientists who caution against putting too much hope in new advances in technology and medicine.

Demographers looked at data from nearly 4,000 Italians above the age of 105 and noticed that, with each passing year, they were no more likely to die than they had been before reaching that age. In other words, after a certain age, the risk for death plateaus.

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“We’re seeing death rates, among extreme ages, go down a little bit,” said Ken Wachter, a professor of demography and statistics at University of California, Berkeley, who helped lead the study. “That means we’re not coming up against a limit to lifespan.”

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A 2016 study examined global demographic data, and concluded that humans have an upper limit of 115 years — with an occasional outlier surpassing expectations. That paper, published in Nature, was rebutted in subsequent papers — with this latest paper serving, potentially, as another.

Here’s what the Science paper found: A person’s risk of dying gets statistically higher with each passing year — until they hit 80. The idea is that those who were less fit, in a Darwinian sense, die out before they hit extreme old age. The survivors, who have proven their mettle as hardy stock, wind up less likely to die with each passing year. After 80, the death rates actually begin to decelerate — and after 105, the death rates plateau, according to the Science study.

Those who have survived to extreme old age — say, 110 years — aren’t any more likely to die than a person who is a few years younger. Rather, the idea is that the most genetically robust people survive into old age — and could potentially continue to live for an indefinite amount of time, if technology advances permit.

The paper’s methodology is “well-done,” but sheds little new light on the concept of mortality plateaus, said Tom Kirkwood, associate dean for aging at the Newcastle University Institute for Aging. Furthermore, it observes trends of aging but does nothing to explain why some people live for such long stretches.

“This kind of demographic study cannot identify the reasons for an apparent plateau, which are rooted in biology and which so far remain elusive,” Kirkwood said.

One scientific faction puts a hard stop on the human lifespan at 115 years. The 2016 paper in Nature found that the maximum reported age of death increased until the mid-1990s, then plateaued. That suggested that despite all the advances in technology since, the upper limit of age could not surpass 115. To increase the limit, scientists would have to develop interventions that would tackle aging on too many different fronts — and that’s just not possible with the current technology we have, said Jan Vijg, chair of genetics at the Albert Einstein College of Medicine and an author of the Nature paper.

Vijg thinks that a mortality plateau observed in the latest research doesn’t disprove his paper.

“If you’re very lucky as a human, have good genes, and are lucky to avoid diseases, you probably do have a higher chance to live just a little longer than others — that’s selection,” Vijg said. “But this is far from saying ‘since mortality no longer increases, that means that humans can continue to live longer and longer.’

“These people are still very close to death.”

There’s a strong business incentive behind the idea that there’s no limit on human longevity. Case in point: Just this week, AbbVie and Google parent company Alphabet said they’d pour an additional $1 billion to fund Alphabet spinout Calico, which is working covertly on aging science. But not everyone accepts the premise.

“I’m not a believer that there is going to be some silver bullet, some magic drug or substance or intervention that will have a major impact on aging overall,” Wachter said. “The hope is that as we understand the interaction between genes and our behaviors, along with environments, toxins, and medicines, we’ll be able to better tune the life course for widespread improvements in lifespan.”

Humans have gradually been extending their lifespans over millennia — with the biggest leaps being made in the past century or so. But our genes, by and large, often date back to caveman times, he said.

“What that shows is that the way our bodies are put together, and our genetic heritage, is very permissive,” Wachter said. “We strongly believe that the patterns we’re seeing — which include this leveling out at extreme ages — partly reflect the processes of evolution.

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