In 1997, at the reported age of 122, Jeanne Calment passed away in the south of France, setting a benchmark for human survival.
Though not all are convinced of the record's authenticity, Calment's purported age at death is now a rough marker for a potential human lifespan. Of the few dozen individuals currently older than 110, the odds are slim to none that any will see their 125th birthday.
Economist David McCarthy from the University of Georgia and Po-Lin Wang, an expert in risk management and insurance from the University of Southern Florida in the US, are a little more optimistic. They think a true record-breaker might be just around the corner.
We can't be blamed for thinking we've squeezed every drop of longevity from our genes. While there are now more centenarians than ever in history, the ceiling for survivability seems stuck in the 11th decade and has been since the last century.
McCarthy and Wang used mortality data from birth cohorts in the Human Mortality Database, employing a Bayesian statistical approach to analyze the lifespans of those born in the same year across 19 currently-industrialized nations.
As the number of people living to such a ripe old age is statistically somewhat limited, the duo applied a function known as the Gompertz law to better estimate the age any individual might be expected to first reach an assumed mortality plateau.
This 'Gompertz Maximum Age', or GMA, should theoretically hint at an upper limit to the human lifespan. If the GMA is fairly constant from one cohort to the next, we can assume a maximum age exists. Advances in medical science might help more people avoid illness and recover from injury, but the distribution of ages we die at will simply be compressed into a smaller range.
On the other hand, if GMA were found to rise between cohorts, there could be a reason to suspect mortality is instead being 'postponed', meaning if there is a cut-off in lifespan hard-wired in our biology, we're yet to see it take effect.
For the most part through history, it seems GMA has remained relatively stable. Improvements in sanitation, health care, and nutrition have predominantly allowed more people to reach old age, compressing the distribution of mortality past a certain point rather than extending it.
Yet there have been distinct periods where this hasn't been the case.
One was among people born in decades past the mid-19th century, where the GMA jumped by around five years. Though the cause isn't clear, the rise was more pronounced among women. It also describes individuals who hit their centenary before 1980, making it possible significant improvements in medical technology and public health measures could be responsible.
A far more significant leap in GMA seems to be at work among people born between 1910 and 1950. Currently aged between 70 and 110, we might anticipate a postponement of mortality equal to around 10 years, implying at least a few retirees just might hit the news by the year 2060 for celebrating some very advanced birthdays.
The trends might also help explain why records appear to have stagnated over the past few decades. Social changes that lead to the postponement of mortality may not affect every cohort equally, meaning those old enough to have broken longevity records may be too old to benefit from measures that lead to a subsequent bout of postponement.
Taken in context with other studies, leaps in medicine and access to social welfare could steadily allow some of our descendants to feasibly add decades to our lives.
Don't invest in the birthday candle industry just yet. The study's conclusions rest on numerous assumptions and speculations, not least of which is the relationship between healthcare and a potential postponement of mortality.
"We emphasize further that cohorts born before 1950 will only have the potential to break existing longevity records if policy choices continue to support the health and welfare of the elderly, and the political, environmental, and economic environment remains stable," the researchers warn.
Far from a reason for hope, the study could serve as a word of caution. Not only could we have more people reaching loftier ages, forced to meet the challenges old age brings with it, a decline in population growth means less support from a youthful community.
As seen in the pandemic's devastating impact on the elderly, society just might not be ready for record-breaking lifespans.
This research was published in PLOS ONE.