The maximum human lifespan could far exceed previous predictions, according to work that challenges the idea that humans are approaching a hard limit on longevity.
The latest research comes in response to a recent high-profile paper that concluded “maximum longevity has hit a ceiling of 114.9 years” – a claim that prompted extraordinary levels of criticism from the scientific community. Now five separate research teams have launched critiques of the work in a series of papers in the journal Nature.
Together they present the case that there is no compelling evidence that we are approaching an upper limit on our mortality – or at the very least, that such a limit may be considerably higher than 115 years.
Prof Jim Vaupel, a specialist in ageing at the Max Planck Institute for Demographic Research in Germany and one of the authors, said: “The evidence points towards no looming limit. At present the balance of the evidence suggests that if there is a limit it is above 120, perhaps much above – and perhaps there is not a limit at all.”
The dispute between Jan Vijg, the geneticist at Albert Einstein College of Medicine in New York who authored the original paper, and the critics, has become unusually heated, with both sides stepping beyond the typically restrained bounds of scientific discourse.
“It’s the worst piece of research I’ve ever read in Nature magazine,” said Vaupel. “I was outraged that a journal I highly respect would publish such a travesty.”
Vijg is equally strident, implying that his critics are, to some extent, simply upset at being confronted with their own mortality.
The original study used the International Database on Longevity, which compiles lists of the age of the oldest person to die in a given year. It found the maximum reported age of death increased rapidly between the 1970s and early 1990s, but then appeared to plateau in the mid-1990s at 114.9 years.
The latest papers argue that this conclusion is wrong and offer a host of more optimistic interpretations. Prof Siegfried Hekimi from McGill University in Montreal said: “You can show the data are compatible with many different trajectories and not at all an ongoing plateau.”
Under one such scenario, lifespans would be predicted to climb steadily upwards, such that the oldest person alive by the year 2,300 would be expected to be 150 years old. “The increase in average lifespan will not suddenly crash into a 115-year limit,” he said.
Hemiki said there was annoyance about the levels of media attention the Vijg paper received, because “people like a number”, despite the fact that “the data were strikingly unconvincing”.
One complaint was that Vijg’s analysis partitioned the data into two time periods – before and after 1995 – on the back of a visual inspection that appeared to show a levelling off around this year. When the two underlying trends were calculated, the period after 1995 had a flat gradient, appearing to confirm the hypothesis.
“That’s something you shouldn’t do in statistics,” said Hekimi. “It’s circular.”
Another problem is that when any data series is segmented, there may appear to be temporary plateaus or even declines, despite an overall upward trend – as seen in long-jump records, for instance.
Another of the critiques notes that the headline result – the flat gradient after 1995 – is based on just 12 data points and could simply reflect the inclusion of Jeanne Calment, a French woman who died in 1997 at the record-breaking age of 122 years. If this datapoint was shifted forward a few years to 2004, the apparent plateau vanished.
Vijg counters that a dataset focused on the oldest people on Earth is always going to be small. “When you look at these super-old people, there are not many of them. That’s kind of the point, isn’t it?”
Maarten Rozing of the University of Copenhagen said there was little to suggest the existence of a “biological clock” programmed to limit the length of life. “We now know not only that the idea of such a clock is highly implausible, but also that ageing is proving to be more amenable to change than used to be supposed,” he said.
Vijg said he accepts “absolutely nothing” in the latest criticisms, dismissing them as statistical nitpicking by those who “hadn’t read his paper properly”.
He compared the suggestion that there was no lifespan limit in sight to Zeno’s paradox, where an arrow is shot at a tree and first travels half the distance and, from the halfway point, half the distance again, in an apparently unending journey.
“They try to come up with intricate models to show that mortality is actually decreasing with very old age,” he said. “It’s worse than science fiction.”
