Is there a limit on how long humans can live?
If there is, we’re not approaching it. That’s the assertion of researchers at the University of Georgia and University of Southern Florida, in a study published this week in the journal PLOS ONE.
Professors David McCarthy and Po-Lin Wang examined current and historical mortality data for people between ages 50 and 100, from 19 industrialized countries like the U.S., U.K., Australia, Canada, France, Italy, Japan, and New Zealand.
They found occasional birth cohorts that tended to live longer, with the cohort born between 1900 and 1950 serving as a prominent example. Members “are experiencing historically unprecedented mortality postponement, but are still too young to break longevity records,” McCarthy and Wang wrote. As the group ages, longevity records could “increase significantly,” they noted. They aren’t certain as to why, but speculate that improvements in public health and medical technology may play a role.
“If there is a maximum limit to the human lifespan, we are not yet approaching it,” they concluded, citing the 1900-1950 cohort’s tendency to push back on life-span expectations.
What’s in an age?
Not every birth cohort has experienced such longevity, however. That’s why, overall, the human lifespan has been slow to increase in recent years.
Ancient Hebrews regarded 80 as the maximum length of human life, while ancient Romans viewed 100 or 110 as the limit. The record for the longest recorded human lifespan is held by Jeanna Calment, a French woman who lived to be 122. When she was born in 1875, the average life expectancy was only around 40 years old.
Life expectancy is relatively easy to calculate—it’s around 76 years in the U.S. But the maximum lifespan, if one exists, is much harder to estimate. While some researchers contend that a natural limit sits around 120, 140, or 150 years, others speculate that a limit doesn’t exist—and that aging doesn’t necessarily lead to death.
“Evolutionary biology provides little support for the idea that there are ‘aging genes’ that simply cause their carrier to grow old and die,” wrote Richard Fargher, a professor of biogerontology at the University of Brighton in the U.K., in a 2016 piece in The Conversation.
“Aging is simply an exponential increase in your chance of death and sickness with the passage of time.”
Some members of a population, Fargher contends, tend to survive the odds—perhaps due to evolutionary fitness and a bit of luck.
Case in point: It appears that hydra—small fresh-water animals—don’t age, and that their chance of death remains fixed over time, instead of increasing. “Extrapolation from laboratory data show that even after 1,400 years, 5% of a hydra population… would still be alive,” he wrote.
As Fargher concluded, “Perhaps the real lesson here is that simple closed questions, in any scientific discipline, are somewhat like asking, ‘Who is the most interesting person?’—intoxicatingly profound and practically useless.”
