by MICHAEL EISENSTEIN
Super-centenarians offer clues as demographers and scientists lock horns over one of the world’s oldest research questions.
In the late eighteenth century, while in hiding from his fellow French revolutionaries, the philosopher and mathematician Nicolas de Condorcet posed a question that continues to occupy scientists to this day. “No doubt man will not become immortal,” he wrote in Sketch for a Historical Picture of the Progress of the Human Mind, “but cannot the span constantly increase between the moment he begins to live and the time when naturally, without illness or accident, he finds life a burden?”
The answer to that question remains the subject of debate. Some researchers posit that modern human lifespans are nearing a natural ceiling, whereas others see no evidence for such a limit. Arguments have often become heated, with research articles occasionally prompting angry letters to journal editors and even allegations of fraud.
“People have drawn a line in the sand with their particular vision of what old age is like,” says Steven Austad, a gerontologist at the University of Alabama at Birmingham. “And now they’re refusing to cross that line, irrespective of what the accumulated evidence suggests.”
Jean-Marie Robine, a demographer at INSERM, France’s national biomedical research institute in Paris, points out that the limits of lifespan sparked curiosity long before Condorcet. “It is possibly the oldest research question we have,” he says. Even if no formal physiological limit exists, reaching the frontiers of survival is no mean feat, and further gains in longevity might ultimately require remarkable advances in medical science, even if the ranks of the world’s centenarians continue to swell.
Plateau, or no?
One of the first efforts to map the boundaries of human lifespan came from the British mathematician and actuary Benjamin Gompertz in 1825. His analysis of demogra-phic records demonstrated that after a person’s late twenties, their risk of dying increased at an exponential rate year after year — sugesting that there is a horizon where that risk finally reaches 100%.
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