Scientists have long argued over whether there is a natural barrier to the human life span, or whether our life expectancy could keep rising, as it has continuously for more than a century. In the latest development in this lengthy debate, a new study argues not only that there’s an upper limit to our life span, thanks to genetic factors, but that we’ve already reached it. From now on, they say, it’s incredibly unlikely any of us will live for more than 125 years, regardless of any increase in healthier habits or stunning advances in medical science.

While a child born back in 1900 had an average life expectancy of around 50 years, a little girl or boy born today can expect to live on average to the age of 80. In Japan, where average life expectancy at birth has risen higher than any country so far, that number is 83. Life expectancy has risen nearly continuously since the 19th century, leading some scientists to speculate that there may be no limit as to how long humans might be able to live.

Jeanne Calment. (Credit: Pascal Parrot / Sygma / Getty Images)
Jeanne Calment. (Credit: Pascal Parrot / Sygma / Getty Images)

But in a new study, published this week in the journal Nature, scientists at New York’s Albert Einstein College of Medicine argue that despite the increases in life expectancy over the past century, it’s highly unlikely human life spans will continue to rise any higher than they are now. They believe there is a natural barrier to the human life span, and that we likely reached the peak of our life expectancy back in the late 1990s, around the time of the death of Jeanne Calment of France. At 122, Calment was the oldest person in the world when she died in a French nursing home on August 4, 1997, and she remains the oldest documented person to ever live.

To reach their conclusions, the researchers examined material from the Human Mortality Database, which compiles mortality and population data from more than 40 countries over the course of the 19th, 20th and early 21st centuries. At first, life expectancy started to rise in the late 19th century because fewer children were dying. In more recent years, more people have been living longer (above the age of 70) thanks to better health, often a result of quitting smoking and adopting better diets, as well as the advent of antibiotics and drugs for heart disease and other chronic disorders.

But when the researchers looked at people age 100 and above, they found that the survival gains peaked around 100 and then declined rapidly, regardless of when people were born. They then turned to data from the International Database on Longevity, which contains detailed records of some 500 people who have lived into extremely old age. Among these supercenterians, as they are known, the oldest age increased rapidly from the 1960s to the 1990s, when it reached 115. But then (close to the death of Jeanne Calment), this rising trend stopped. Ever since, the maximum life span for humans has actually regressed, hitting a plateau of around 110 years.

An Indonesian man, named Mbah Gotho, claimed to be 146 years old, is the oldest human in world's history shows his identity card to press members at his family house in Sragen, Central Java, Indonesia. (Credit: Anadolu Agency / Getty Images)      (Photo by Dasril Roszandi/Anadolu Agency/Getty Images)
An Indonesian man, named Mbah Gotho, claimed to be 146 years old, is the oldest human in world’s history shows his identity card to press members at his family house in Sragen, Central Java, Indonesia. (Credit: Anadolu Agency / Getty Images)
(Photo by Dasril Roszandi/Anadolu Agency/Getty Images)

It’s not climate change, overpopulation, obesity or other current issues that are to blame, the researchers say. Instead, it’s all about genetics. The aging process involves an accumulation of damage to DNA and other molecules in the body, and though our bodies can repair some of this damage, there’s a limit to how much can be fixed. As Jan Vijg, a professor of genetics at Albert Einstein and lead author of the new study, put it in a press release: “While it’s conceivable that therapeutic breakthroughs might extend human longevity beyond the limits we’ve calculated, such advances would need to overwhelm the many genetic variants that appear to collectively determine the human life span.”

According to Vijg and his colleagues, 115 years old is realistically the most advanced age that most humans can expect to reach; the odds of someone passing 125 years of age are only one in 10,000. Today, the world’s oldest documented person is 116-year-old Emma Morano of Italy, who was born in November 1899. (Although a man in Indonesia named Mbah Gotho claims to be 145 years old, his age has yet to be independently verified.)

Susannah Mushatt Jones, the last living American to have been born before 1900, held the title of world’s oldest person until her death last May in Brooklyn, New York. Mushatt Jones had been born in Alabama in July 1899, during the presidential administration of William McKinley. At the time of her death, the next-oldest American was only 113 years old.