To see if that perceived plateau was real, Dong, Milholland, and Vijg turned to two international databases on longevity and worked out the oldest individuals who died in any given year. They specifically looked at France, Japan, the United Kingdom, and the U.S.—the four countries with the most supercentenarians, people who live to 110 years or more.

The data were clear. Between the 1970s and early 1990s, our maximum age rose from around 110 to 115—and then stopped after 1995, shortly before Jeanne Calment died. In fact, Vijg’s team calculated that in any given year, the odds that at least one person in the world will live past their 125th birthday are less than 1 in 10,000.

Despite sanitation, antibiotics, vaccines, and other medical advances, the oldest living people simply aren’t dying any later. They’re unlikely to either, regardless of calorie restriction, drugs like rapamycin, and all of our other efforts to slow the flow of sand through the hourglass. “In science, you never know,” says Vijg. “But I’ve not seen anything that I think would break through the ceiling.”

The ceiling is probably hardwired into our biology. As we grow older, we slowly accumulate damage to our DNA and other molecules, which turns the intricate machinery of our cells into a creaky, dysfunctional mess. In most cases, that decline leads to diseases of old age, like cancer, heart disease, or Alzheimer’s. But if people live past their 80s or 90s, their odds of getting such illnesses actually start to fall—perhaps because they have protective genes. Supercentenarians don’t tend to die of major diseases—Jeanne Calment died of natural causes—and many of them are physically independent even at the end of their lives. But they still die, “simply because too many of their bodily functions fail,” says Vijg. “They can no longer continue to live.”

Why should life come to such a crashing halt? Imagine that you have an animal that doesn’t age. Despite its immortality, it can still starve, succumb to accidents, or fall to predators. Eventually, its luck always runs out. This imaginary creature should have a demography much like ours—lots of young individuals and fewer old ones. As such, evolution should favor genetic changes that offer advantages during early life—say, in growth or reproduction. By contrast, genetic changes that cause harm during later life would be ignored—they hardly matter when so few individuals reach those ages anyway. That’s why organisms age—evolution naturally and inexorably prioritizes the young in favor of the old.

But if early development and childhood experiences are so important to our future health, it’s notable that today’s centenarians were born in the 1900s. It might be that longevity records “haven’t yet seen the impact of the improved sanitation, healthcare, vaccinations, and hygiene advances that took place in the 1930s and later,” says Holly Brown-Borg from the University of North Dakota. Or perhaps, “our poor diets and lack of exercise have countered those gains.”