For the elderly, life becomes increasingly precarious: Getting the flu could be life-threatening; a simple fall can be life-ending. (Falls are now the leading cause of accidental death for this age group in the U.S.) A study published in Science last week challenges this intuition: The team of scientists led by Elisabetta Barbi, a demographer from Sapienza University, claims that life actually ceases to be increasingly dangerous after a certain age. The finding is nonintuitive and interesting, but the reporting on it has been a bit fantastical. To take a representative example from Nature’s coverage of this work: “That would mean that someone like Chiyo Miyako, … the world’s oldest known person, could live for years to come—or even forever, at least hypothetically.” But despite these sorts of claims, the finding itself has no such implication. Chiyo Miyako—like the 100 billion homo sapiens who came before and all those who will come after—will definitely die someday, just like the rest of us.
As is often the case, the confusion stems from language. The study’s central claim sounds deceptively clear-cut: “Mortality rates level off at extreme age.” But what do these words actually mean? The first half, “Mortality rates level off,” is the real rub; let’s dissect it carefully. In this context, a “mortality rate” is the probability that a person will die at some point between two birthdays. This probability depends on your age. When you are 15, your mortality rate is relatively low: 0.04 percent, or about 1 15-year-old in every 2,500. As you age, your mortality rate rises. For 60-year-olds, about 1 in 100 won’t make it to 61. About 1 in every 3 99-year-olds won’t make it to triple digits.
Imagine playing a morbid game of heads or tails every year on your birthday. Before blowing out your candles, you flip a coin: heads, you live until your next birthday, tails, you die. When you are young, the coin is biased in your favor; maybe it’s bent in a way that makes landing tails extremely unlikely. But as you pass from childhood to middle age, from middle age to old age, the coin slowly unbends.
Until, according to the authors of the paper, you reach the magic age of 105. At 105, the coin has become entirely flat and stays that way forever. On your 105th birthday, you flip a fair coin: 50 percent chance of dying. On your 106th birthday, the same fair coin. And same for your 107th, and so on until you inevitably flip tails and croak. The game is still cruel, but it stops increasing in its cruelty. In other words: “Mortality rates level off at extreme age.”
This conclusion is not entirely accepted among longevity experts, with several scientists doubting the study’s finding based on a combination of data quality and biological feasibility. But even assuming that the finding is correct, this generous picture of aging is a far cry from eternal life.
Even if mortality rates level off at 50 percent for people older than 105, these supercentenarians still have to flip the coin every year. No free passes: Every year you must flip. Strictly speaking, this doesn’t make extreme aging impossible, just exceedingly improbable. For instance, it’s not impossible for someone who is 105 to flip 16 consecutive heads and live past the biblical age maximum of 120. The chances of this happening, however, are approximately 1 in 100,000. This means that if we filled Citi Field twice over with 105-year-olds, we would expect about one of them to live until 121. Unlikely, but not impossible: Jeanne Calment, the oldest person ever to live, died at 122.
What about the chances of a 105-year-old flipping 105 more heads and living to 210? This is about 1 in 40 nonillion. (Written all the way out, that’s 1 in 40,000,000,000,000,000,000,000,000,000,000.) To put that in perspective, it’s slightly more likely that you will win the New York state lottery twice, then get struck by lightning twice before being eaten by a shark. Possible? I guess so? But only in the inspirational-speaker sense of “Anything is possible.” I just wouldn’t bet my life on it—and even if you manage this feat, on your 211th birthday you still have to flip the coin again. Sooner or later, probability will kill you.
If it wasn’t mathematical confusion that gave some the hope of limitless life, then it could only be the limitlessness of human optimism. An eternal optimist may read the last paragraph and think, “One in 40-nonillion is small, but it’s still not zero!” I might try to argue that mathematically, the probability of flipping infinity heads is not just close to zero, it is zero. But life is too short.