But statistics is a cruel science, and Gompertz knew it too. According to his data, the risk of dying at age 92 was so high that it would take an incredibly large number of humans to reach that age before finding a single person who lived to be 192. Three billion humans, to be precise, 30 times more than ever born. And yet, Gompertz found himself hampered by his dataset. So few humans made it past the age of 90, it was hard for him to really know what death rates looked like at very old ages. Did his results indicate an insurmountable limit to human lifespan, or just a temporary cap that could be lifted with advances in medicine?
Modern demographers have picked up where Gompertz left off, sometimes with surprising results. In 2016, Jan Vijg and colleagues at the Albert Einstein College of Medicine in New York concluded that death rates beyond age 100 were starting to rise rapidly, capping the human lifespan at around 125 years. Two years later, another group of demographers, this time led by Elisabetta Barbi of La Sapienza University in Rome, came to the opposite conclusion. She argued that human death rates increase exponentially until age 80, at which point they slow and then level off after age 105. Barbi’s research raised the tantalizing prospect that there is no upper limit to human lifespan, just as Gompertz wondered.
If death rates really plateau at a certain age, then extreme longevity is just a numbers game, Robine says. Suppose 10 people reach the age of 110 and the risk of one of them dying each subsequent year has plateaued at 50%. Five of them would be expected to reach the age of 111, two or three to reach the age of 112, one or two to reach the age of 113, one to reach the age of 114, and no one to reach the age of 115. of a person reaching 115, you have to double the number of people reaching 110, and so on. In other words, the upper limit of lifespan is only a factor of the number of people who survived the previous year. But those numbers all depend on exactly what and where the mortality plateau is. The problem is that the data available to calculate this is not very good.
The best global death dataset is the Human Mortality Database, but it groups all people over the age of 110 into one group. Then there’s the International Longevity Database (IDL), a dataset that includes living and deceased people who have reached the age of 105 and beyond, which Robine helped set up. in 2010. At its peak, the IDL had data from 15 countries, but tightening data privacy regulations mean that coverage of the most recent data is spotty. Some countries have since partially removed what they included.
Japan, for example, has more centenarians per capita than anywhere in the world, but in 2007 its Ministry of Health, Labor and Welfare reduced the amount of publicly available data on its centenarians, which means one of the richest sources of very long-term information. – experienced people no longer produce useful information. And in countries that produce good data, the process of validating and researching birth records that can date back to the early 19th century is still laborious and frustrating. To validate Jeanne Calment’s age, Robine asked the supercentenarian about her early life, checking her answers against church records, censuses and death certificates. Even so, the IDL contains records of just under 19,000 people, living and dead, from 13 countries. But for Robine, it is vital to harvest even more.
