How triumphant he looks, S. Jay Olshansky, sitting like that, his head buried in the cushions of his fleece seat, the sun in his eyes. A neighbor mows the lawn, and he, sociologist that he is despite his false appearance of a wandering retiree, talks about his academic work without flinching. As if it was there, from his suburban garden in the suburbs of Chicago, in this position, that he had “resolved” one of the main demographic controversies of the last thirty years.
The American demographer, very renowned in his field, has something to be proud of: he has just published this Monday, October 7 in Nature Aging new work where he refutes, with supporting figures, the hypothesis according to which it would be possible to extend the average human lifespan to infinity. A seemingly naive idea but very seriously debated on a scientific level: since the 1990s, multiple experiments have made it possible to extend the life expectancy of certain laboratory animals, sometimes as much as quadruple it. Many saw this as a sign that the same could be true for humans.
Since then, two almost irreconcilable camps have clashed: that of “limited life”, guided by S. Jay Olshansky, for whom the organism is “genetically programmed” to wither and die. And that of “extensible longevity” led by James Vaupel, founder of the Max Planck Institute of Demography (Germany), a convinced “borderless” person. The controversy never really went beyond the scientific framework, but it gave rise to serious arguments between the two researchers, both publicly and privately.
Serious arguments
James Vaupel died in 2022, before a consensus emerged. But the study by S. Jay Olshansky could well change the situation: it observes a sharp slowdown in the growth of life expectancy since the 1990s, in the eight best-off countries (Australia, France, Italy, Japan, South Korea, Spain, Sweden and Switzerland). And this, even if at the same time the main risk factors for dying have become less significant, and mortality has fallen over the period.
In videoconference, S. Jay Olshansky does not go so far as to speak of “victory”, scientific modesty obliges. It must also be said that his work does not constitute proof of the intrinsic limits of our organisms – biological observations are necessary for that. But the blow to Vaupel’s argument is no less important: excluding a cataclysm of the type of world war or epidemic, he bet on an infinite continuation of the rate of increase in life expectancy reached until the end of the 1990s, of the order of three months per year. This is not what has been observed in the most recent period, where according to S. Jay Olshansky’s publication, gains have slowed to less than two months per year.
The wind was nevertheless favorable. For 150 years, progress in life expectancy in Western countries has been made almost exclusively on children. It was then thought that it was not possible to make adults live longer. Then the improvement in living conditions since the 1950s shattered this glass ceiling, raising significant hopes. The number of centenarians began to double, first in the 1960s, then every 10 years, while life expectancy continued to increase at a sustained rate.
Generation 2000, centenarian generation?
It is on this boom that James Vaupel builds his projections, published in Science in 1998. His arguments made a lot of noise at the time: that most people could live until 80, 90 or 110 years old would have immense societal consequences, on pension and insurance systems, or even on conservatism, stronger in these age groups. In joy, James Vaupel then indulges in a bet: it is certain, he says, half of the people born after 2000 will live 100 years.
Here again, recent developments seem to prove him wrong. “As it stands, the chances of survival after 100 years are not expected to reach 15% for women and 5% for men” by the end of the century, writes S. Jay Olshansky, who at a younger age bet that no individual would ever exceed 150 years old. An estimate consistent with other work, published in Nature And Journal of the American Statistical Association in 2016 and 2017. The latter set a theoretical limit around 115 years.
Nothing insurmountable all the same: the Frenchwoman Jeanne Calment died at 122, and other supercentenarians will surely beat this record. But exceeding this age should remain the exception, according to this work. Firstly for statistical reasons: “Today deaths before the age of 60 are exceptional. Progress can be made on the mortality of older people, but it will be of little benefit”, explains Jean-Marie Robine, director distinguished research fellow at Inserm.
A statistical ceiling, another, biological
Reducing mortality among those over 70 and 80 does not have the same effect as saving an infant. In one case, a few years are added. In the other, a whole life. The first only very slowly increases life expectancy, the second makes it jump. What’s more, a second limit is emerging: “Once we have eliminated deaths before the age of 80, we will still have to overcome the intrinsic fragility which sets in at this age and makes us vulnerable to the slightest shock or cold snap”, continues the specialist.
For the expert, most of the progress in terms of life expectancy has already been made. Medical innovations could still push back this glass ceiling a little: “The anti-aging drugs currently in development could save a little more time,” says Coleen T. Murphy, biologist at Princeton University, and discoverer. numerous genetic modifications allowing us to gain years of life in the laboratory. Perhaps these remedies will one day be effective enough to cause a new jump in life expectancy. But no demographer has dared to bet on this.
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