# The human life span is theoretically limitless, a study suggests - adding fuel to a longstanding debate about our mortality

Odette Ambulher celebrates her 111th birthday in a retirement home in the French village of Laigne-en-Belin in October 2012. BSIP/Universal Images Group via Getty
• The oldest person who ever lived reached age 122, but research indicates humans could live longer.
• After people hit 108, they have a 50% chance of living until their next birthday every year, one study says.
• Theoretically, that suggests there is no limit to the human life span, but biologists disagree.

A person's chance of dying doubles about every nine years.

But that changes if you reach 108, according to a mathematical modeling study published last month. After that, your chance of death plateaus to an even 50-50 each year.

"Think of it like a coin flip - when you reach 108, you flip a coin on your birthday. If comes up heads, you live to your next birthday. If it comes up tails, you die before turning 109," Anthony Davison, a statistician at the Swiss Federal Institute of Technology who co-authored the study, told Insider. "And if you get to a subsequent birthday, your probability of dying doesn't change."

By that logic, Davison's team wrote, this "would imply that there is no limit to the human lifespan."

It's a controversial idea - one that has not, of course, been borne out by reality.

The longest a human has ever lived is 122 years, 5 months, and 14 days - a record set by Jeanne Calment in France in 1997. The medical and technological advances of the last quarter-century haven't led anyone to pass that threshold, despite what statistical models suggest is possible. And although a human's average life expectancy has increased by decades in the last 100 years or so, our maximum life span hasn't shifted anywhere near as significantly.

Many biologists think extending human life to that degree is currently impossible. But they have long butted heads with mathematicians over the question of how much time we get on Earth.

## Your chance of making it to 130 is less than one in 1 million

To come up with their numbers, Davison's team looked at mortality data from people who reached or passed age 105, including 1,100 supercentenarians (people age 110 or older), across a dozen European countries, Canada, and the US.

They found that fewer men reached these ages than women - the ratio was one man to every 10 women. But the 50-50 chance of survival was about the same across genders and geographic locations once people reached 108.

Still, even Davison said his results don't mean people can live forever. There's a catch to the coin toss: The population of people over 108 gets halved every year. So if 1,000 supercentenarians flip their coins, on average, 500 will die. Then 250 of those remaining will die the following year.

By extrapolating that math, Davison's group concluded that a person's chance of making it to 130 is less than one in 1 million.

Brandon Milholland, a geneticist at the Albert Einstein College of Medicine who was not involved in the study, told Insider that while it's statistically possible to live to any age, the probability is so exceedingly small that it doesn't make sense to assert there's no limit to the human life span.

In that sense, he said, the new study makes "a mountain out of a molehill."

"Someone could even live to 1,000, but the probability of that is one in 1 quintillion," Milholland added. (If all the humans who have ever lived in the history of the species were totaled up, we'd still fall short of 1 quintillion.)

## Think of life like a log flume ride

Biologists assert that our bodies eventually reach a point after which the next disease or illness we get will kill us - that's our maximum life span.

Andrei Gudkov, chair of cell stress biology at Roswell Park Comprehensive Cancer Center in Buffalo, New York, said that in order to calculate that maximum, experts look at the body's resilience. That's its ability to return to normal functioning after an illness or biological stressor.

Think of your life like a boat on a log flume ride - except the walls meant to keep the boat from falling out of the water get progressively shorter as the ride progresses. Those walls represent your body's resilience, which typically declines as you age. Imagine illness, then, as a force that pushes the boat toward the walls. At the beginning of your life, when the walls are high, your boat stays on track. But as you get older, those walls shorten, and the same pushes eventually force the boat over the edge and off the ride.

"When you reach the place where resilience goes to zero, even a small disease will make this final drop happen," Gudkov told Insider. "You can die from anything."

Resilience declines with age because as our cells duplicate over our lifetimes, they collect mutations. Eventually, those mutations render a cell incapable of functioning correctly.

But the precise limit of our species' maximum life span remains up for debate. A 2016 study suggested the upper end is 150, though research from Milholland's group the same year suggested an age closer to 125.

The new study's results, meanwhile, suggest that someone should be able to beat Calment's record by at least eight years.

"It is implausible that any upper limit to the human lifespan is below 130 years or so," the authors wrote.

Léo Raymond-Belzile, one of Davison's co-authors, told Insider that he "could see Joan's life record being broken in my lifetime."

## 'You've maxed out your chance of death'

The new study also brings up another hotly debated topic among aging experts: whether our risk of death ever flatlines.

A mathematical model from the 19th century, called the Gompertz equation, showed that a person's mortality risk increases exponentially as they age - that's how health insurance companies calculate premiums.

But Davison's study refutes that idea. His group's calculation instead suggests that after you reach 108, "you've maxed out your chance of death," as Richard Faragher, a biogerentologist from the University of Brighton, put it.

Faragher, who was not involved in the study, added, though, that "it's a poor comfort because your chance of dying remains so high."

Milholland disagrees. Evidence supporting a mortality plateau is weak and disputed, he said, and it doesn't make sense that the biological drivers that increase our chances of dying would suddenly stop.

"Even if such plateaus exist, they are not even compelling evidence that there is no limit to lifespan," he said.

One thing aging experts do agree on is that while average life expectancy has increased, there hasn't been a corresponding increase in our maximum life span.