Jean-Marie Robine is not impressed by your centenarian grandma. Sure, she’s sprightly for her age, but how unusual is making it to 100, really? Robine is a demographer and longevity researcher, and in his home country of France alone there are 30,000 centenarians; 30 times more than there were half a century ago. Add up all the centenarians worldwide and you get to 570,000—an entire Baltimore’s worth of extremely long-lived humans. Having a birthday cake with 100 candles is nice, but nowadays it’s nothing special.
To really pique Robine’s interest we need to up the longevity stakes a little. He is an expert in supercentenarians: people who live to 110 or even longer. In the 1990s Robine helped validate the age of the oldest person who ever lived. Born in 1875, Jeanne Calment lived through 20 French presidents before dying in 1997 at the age of 122, five months, and 15 days. Since then Robine has become a collector of the super long-lived, helping run one of the largest and most-detailed databases of extremely old people.
For Robine, each supercentenarian is a crucial datapoint in the quest to answer a big question: Is there an upper limit to the human lifespan? “There are still many things we don’t know. And we hate that,” says Robine. But there is an even more fundamental question that undercuts the whole field of longevity research. What if—in our quest to push the limits of human lifespan—we’re looking for answers in all the wrong places?
If you’ve ever read an interview with a supercentenarian, there is one question that will inevitably come up: What’s the secret? Well, take your pick. The secret is kindness. Not having children. Connecting with nature. Avoiding men. Or, being married. Smoking 30 cigarettes a day. Not smoking 30 cigarettes a day. Drinking whisky. Abstaining from alcohol altogether. We mine the lives of the super-old for hints on how we should live our own.
But this is the wrong way to approach the question, says Robine. His style is to step back, take a look at how many supercentenarians there have been, and figure out when they lived and died. The limits of human longevity won’t be found by looking at individuals, he believes, but by examining super-long-lived people collectively. It’s a statistical puzzle: to crack it, you need to know exactly how many people died at age 111, 112, 113, and so on, to work out the likelihood that a supercentenarian won’t make it to their next birthday.
In 1825, the British mathematician Benjamin Gompertz published one of the first attempts to calculate the limits of human longevity following this approach. Armed with birth and death records from Carlisle and Northampton, Gompertz calculated how someone’s risk of dying changed as they got older. Gompertz found that after a person hit their late twenties, their risk of dying in the subsequent year kept going up, year after year. But at age 92 something curious happened. Their annual chance of death leveled off at 25 percent per year. This finding was odd. It suggested to Gompertz that there was no upper limit to human aging. Theoretically, he mused, there was nothing in his data suggesting that humans couldn’t live for many, many, centuries—just like the lives of the patriarchs in the Bible.