Dispute Erupts Over the Limits of the Human Lifespan
Scientists from around the world are refuting a controversial claim last fall that the progression of the human lifespan is limited to around 115 years.
Now scientists from around the world are refuting this claim.
The original research paper, by Jan Vijg and his colleagues at the Albert Einstein College of Medicine, was published in Nature last October. “Our results strongly suggest that the maximum lifespan of humans is fixed and subject to natural constraints,” they wrote.
The researchers settled on the magical 115 number by using two databases: the International Database on Longevity and the Human Mortality Database. They identified the five top maximum reported ages at death (MRAD) for four countries, and plotted them on a graph. These four countries (France, Japan, UK, and the US) have the highest number of “supercentarians,” people who live to be 110 or older.
The graphs led the authors to conclude that the maximum human lifespan has already been reached. They found that the MRAD continued to rise until 1990s, around the time of the death of Jeanne Calment, the world’s longest living person on record, who died at the age of 122. Since then, Vijg and colleagues argued, the MRAD has plateaued.
But almost immediately after the study was published, controversy and criticism followed. This week, Nature released separate critical responses from five unaffiliated research groups. The researchers of the Dong et al. study responded to each one.
“Their whole article was a fairly large extrapolation,” Nick Brown, a Ph.D. student in psychology from the University of Groningen and a member of one of the research groups, told Seeker. There is such a small sample size of supercentarians around the world that “the result isn’t even statistically significant,” he added.
Other scientists pointed to flaws in study design and methodology.
“They made basic errors in how they went about assessing the statistical significance of their conclusions,” wrote Maarten Rozing, a longevity researcher from the University of Copenhagen who joined two colleagues in criticizing the paper, in an email to Seeker. “We therefore think that their findings do not contradict the possibility that lifespan will continue to increase.”
Researchers also criticized the study authors for splitting the data in 1994.
“If the partition date is moved two years, from 1994 to 1996, it no longer shows a lifespan plateau,” noted another group of critics.
None of the dissenting researchers claimed that immortality is possible. The common consensus seems to be that there is simply not enough information to know whether or not human life will biologically end at a fixed point.
“The right answer is that no limit to human lifespan can yet be detected,” wrote Siegfried Hekimi, a biologist at McGill University and another critic of the paper, to Seeker over email. But, he added, “it does not mean there is no such limit.”
Brown echoed this sentiment.
“We would say that there is no evidence at all right now for a limit” on the human lifespan, he said. But that doesn’t mean a limit will not exist in the future. “It would be a bit like coming along in 1940 and saying airlines aren’t going to get any faster because you can’t put more propellers on the plain,” Brown remarked.
There was a technological limit on flight speed at that time, but no one had yet foreseen the invention of the jet engine. New anti-aging technologies are being developed every day — right now, there’s just no way to know if a hard limit exists.
Vijg, responding to the criticism, disputes that this was his claim in the first place.
“We would never claim that there is a hard ceiling,” he told Seeker. “It’s always possible that something happens that we cannot foresee.”
But in terms of current technology, he went on, their research shows that it is highly unlikely for anyone to live past the age of 115 without significant medical advances in the near future.
Vijg also disagrees that there was anything wrong with his team’s statistics. They had a small sample size, he acknowledged, but with supercentarians, “you’re dealing with a rare breed.”
And while neither Vijg or his co-authors are demographers or statisticians themselves, Vijg pointed out that all three peer reviewers of their article were “top of the line demographers.”
“If the sample size was too small, believe me, we would have known it,” he said. “This is Nature for God’s sakes.”
Nature is indeed a well-regarded academic journal, though some people have used the debate over this paper as an opportunity to criticize the secrecy of the journal’s peer-review process.
In the end, finding a maximum age number might not even matter. Most scientists who focus on aging are more concerned with average lifespan anyway, Brown pointed out.
“This is a completely irrelevant measure to almost everybody except for the people who like reading newspaper stories about extremes,” Brown said.
He characterized the dispute over the findings as a perfect example of what has been coined “Sayre’s law.”
“Academic politics,” said Columbia University professor Wallace Sayre in 1973, “is the most vicious and bitter form of politics, because the stakes are so low.”