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A brief history of human longevity

AgeUpLongevity

Here’s a narrative you’re probably familiar with:

During the Stone Age, back when our cavemen and cavewomen ancestors were roaming the world and fighting off saber-toothed cats with big ole’ clubs, the typical person would be lucky to live past his or her teenage years. And only as humans began developing agriculture, civilizations, and more sophisticated technologies did human life expectancy increase, growing steadily over the centuries.

The only problem is… that’s not really how it happened (except for the saber-toothed cat part, that kind of thing happened all the time.)

In reality, the history of human longevity is much more nuanced. Turns out, human life expectancy didn’t increase gradually, year over year, in a straight line. Instead, it grew in fits and starts, and only after the advent of modern medicine did it really start to take off.

That being said, there’s no denying we’ve come a long way.

Fifteen thousand years ago, life expectancy at birth for the global population was likely somewhere between 20 and 30 years. Today, the global life expectancy at birth is 72 years. In the United States, it’s 78.6 years, and in Japan, where people enjoy the highest life expectancy in the world, it’s a whopping 83.7 years.

So, how did we get here from there? What were the major milestones along the rocky road of human longevity? And, perhaps most importantly, where will that road lead us in the future?

Lifespan vs. life expectancy

Before we dive in, here’s a quick primer on the difference between lifespan and life expectancy, as it’s easy to get the two concepts mixed up.

Lifespan is the length of time that an individual lives.
Life expectancy is the average length of time that an individual can expect to live.

At first glance, the difference between lifespan and life expectancy may appear subtle, but as Stanford University historian Walter Scheidel explained in a BBC interview, “there is a basic distinction between life expectancy and lifespan. The lifespan of humans—opposed to life expectancy, which is a statistical construct—hasn’t really changed much at all.”

And he’s right. Research published in the journal Biogerontology shows that our maximum lifespan is approximately 125 years, which means that under ideal conditions, a person will “top out” at age 125. That’s the upper limit. And that upper limit really hasn’t moved much since the Stone Age.

Thousands of years ago, a person could—and some people did—live well into their hundreds. Of course, those people were extremely rare. Which is why, from a statistical perspective, it’s much more useful to look at life expectancy (the average) versus lifespan (the maximum), when trying to learn something about how human longevity has changed over time. With life expectancy, you’re not just looking at individuals who’ve reached old age—you’re looking at an entire population, which includes people who died young, along with those who died as a result of accidents, infections, pandemics, and wars.

(And yes, for our Stone Age ancestors, we’d need to factor in all of those people getting eaten by saber-toothed cats.)

Dawn of the grandparents: the first big milestone in human longevity

English philosopher Thomas Hobbes argued that humans who lived in a state of nature had lives that were “nasty, brutish and short.” And when they look back on the earliest days of humanity, most scholars tend to agree. As Kate Wong, a senior editor of Scientific American, once wrote: “For most of human evolution, our ancestors mostly lived fast and died young.”

Then, 30,000 years ago, there was a major shift. A rare variety of human began appearing with more and more frequency, becoming commonplace in Stone Age families.

That rare variety of human, of course, was the grandparent.

In her article “The Evolution of Grandparents,” paleoanthropologist Rachel Caspari explains that it was only 30,000 years ago that humans began living long enough (30+ years) on a consistent basis to allow for three generations to live concurrently. This influx of grandparents likely facilitated the passing down of knowledge and cultural practices from generation to generation, contributing to an increase in the development of new tools and new types of art.

Life expectancy in ancient Rome

After human life expectancy reached 30 years some 30,000 years ago, one might expect that life expectancy would’ve kept rising, going up and up and up. But it didn’t.

Case in point: In his paper “Demography and Roman Society,” classics and history professor Tim. G. Parkin used ancient tombstone epigraphs to estimate the life expectancy of the average Roman citizen. The figure he came up with: 25 years. For those of you keeping track, that means life expectancy—at least in Ancient Rome—was five years lower than the global life expectancy had been tens of thousands of years before. What gives?

For starters, it’s important to remember that life in an ancient city could be just as “nasty, brutish and short,” as life out in nature, if not more so. More humans (plus the presence of livestock) meant more filth and disease.

However, it’s also important to consider that up until now, we’ve been talking about life expectancy only in terms of life expectancy at birth. That means infant mortality and childhood deaths, which were considerably higher back then, have a huge effect on the final number.

A better way to measure life expectancy, some researchers argue, is to strip away the deaths from those early years and focus only on people who’ve reached adulthood. Here’s a simple (but incredibly sad—you’ve been warned) thought experiment to prove their point:

Imagine there’s a pair of twins. One dies in the first year of life, the other dies at age eighty. Technically, the life expectancy of that two-person population would be 40 years. But when trying to understand the history of human longevity, how useful is looking at an average like that? Wouldn’t you get a clearer picture of longevity by only looking at people who’ve already survived into adulthood?

In the case of Ancient Rome, Parkin found that for people who made it to the age of 25, their life expectancy skyrocketed to 53 years.

Life expectancy in medieval England

The trend of having a low life expectancy at birth and a significantly higher life expectancy during adulthood continued into the Middle Ages. As the BBC reported, the life expectancy at birth for males born between 1276 and 1300 was just over 31 years. But for those who reached age 20, it jumped to 45 years. And if they reached 30, living into their fifties became likely.

Data from statistician H.O. Lancaster’s study “Expectations of Life” offers a more in-depth look at the life expectancy of English males during the High and Late Middle Ages (and beyond). Specifically, Lancaster looked at life expectancy for aristocrats who’d reached 21 years of age from the years 1200 through 1745. Here’s a timeline that lays out what he found:

  • 1200-1300 | Life expectancy: 43 years
  • 1300-1400 | Life expectancy: 24 years*
  • 1400-1500 | Life expectancy: 48 years
  • 1500-1550 | Life expectancy: 50 years
  • 1550-1600 | Life expectancy: 47 years
  • 1600-1650 | Life expectancy: 43 years
  • 1650-1700 | Life expectancy: 41 years
  • 1700-1745 | Life expectancy: 43 years

See that asterisk (*) up there? That’s the Black Death (aka the Plague), one of history’s largest and most horrific pandemics, which killed as many as 200 million people on the Eurasian continent between 1347 and 1351. As you can see in the timeline above, the Black Death had a massive effect on life expectancy at adulthood. But as you can also see, that effect was temporary. Over the course of the next several centuries, life expectancy, after fluctuating briefly, leveled out and returned to post-Plague levels.

One caveat here: Remember that the dataset above is from a bunch of aristocrats, not your average Joe serf out in the English countryside, which means these guys would have had better access to food and medicine, and would have paid better attention to their personal hygiene than the typical person. From a longevity standpoint, this put them at a huge advantage.

Enlightened thinking leads to the “health transition”

While looking at life expectancy at adulthood can be helpful for making certain statistical comparisons, ultimately it ignores the reality of the world we live in. And it’s a world where for thousands of years, child mortality rates were staggering. As recently as 1800, 43% of newborns globally died in their first five years of life, according to data from Gapminder.

This helps explain why in 1820, global life expectancy at birth was still just 29 years, according to a study by historian James C. Riley. The good news: Starting around the 1800s, attitudes toward science and health began to shift, and humanity entered what Riley refers to as a “health transition.”

“Between 1800 and 2000 life expectancy at birth rose from about 30 years to a global average of 67 years, and to more than 75 years in favored countries. This dramatic change was called a health transition, characterized by a transition both in how long people expected to live, and how they expected to die.”

James C. Riley

Prior to the health transition, one of the biggest underlying causes of infant mortality—and premature death in general—was infection. What it really came down to was that surgeons and other “medical professionals” at the time weren’t doing the basics, like sterilizing equipment, or washing their hands before treating a wound or performing surgery. (It took until nearly the 20th century for consensus to form around the germ theory of disease.)

Beyond that, people lived in generally squalid conditions. Before modern plumbing and sewage systems, getting rid of human waste was a major issue—an issue that, in most cases, was not dealt with properly. Contaminated water would lead to outbreaks of typhoid and cholera, killing millions of people around the globe.

Coupled with advancements in medicine, like Alexander Fleming’s discovery of penicillin in 1928, improvements to sanitation led to the first big jump in human life expectancy in the last 30,000 years (give or take). In 1913, global life expectancy at birth reached 34 years. In 1950, it jumped to 48 years. By that same year, 1950, child mortality had dropped from 43% (in 1800) to 22.5%.

Flash forward to 1973: global life expectancy at birth is now 60 years, and child mortality is down to 13.7%.

Jump to the year 2001, and life expectancy reaches 66.6 years, while child mortality drops to 7.4%.

It’s amazing to see how life expectancy was able to shoot upward in such a short amount of time, after remaining nearly static for thousands and thousands of years. It’s a change that happened so fast, society is still struggling to keep up.

Human longevity: where do we go from here?

Since the 1800s, the odds of dying young have steadily declined. Today, the global child mortality rate has dropped to 4.5%. In the United States, it’s dropped to 0.7% (and in Sweden, 0.3%). Meanwhile, the rise of antibiotics and vaccination programs means fewer and fewer people are dying of communicable diseases like tuberculosis, pneumonia, and smallpox.

Thanks to these changes, the average person now enjoys a life expectancy at birth of 72 years. And for Americans, it’s 78.6 years. This extraordinary growth, however, has not come without its challenges.

In many countries, older people are beginning to make up larger and larger portions of the population, and providing care to all who need it is becoming more and more difficult. In 1900, just 4.1% of the U.S. population was 65 or over. By 2015, that number was 14.9%. And while communicable diseases have had less of an effect on mortality over the years, non-communicable diseases—like stroke and heart disease—are now among the world’s leading causes of death.

When it comes to increasing human life expectancy, solving problems like heart disease and cancer will be essential. And with suicide and drug crises also posing distinct challenges, some are pessimistic as to whether or not life expectancy will continue to grow. In the United States in particular, growth in life expectancy appears to be stagnating. Case in point: between 2016 and 2017, life expectancy actually dropped a tenth of a year, from 78.7 to 78.6. (This may seem small, but considering it’s representative of 300 million people, a tenth of a year is a lot of change in total lifespan lost.)

Does that mean, as a species, we’ve reached peak life expectancy? Probably not.

A 2018 study published in the Lancet shows that between now and 2040, human life expectancy will continue to grow. According to the study, Americans can look forward to an average life expectancy of 79.8 years in 2040—an increase of 1.2 years. But it’s the Spanish who will be the big winners, with their average life expectancy predicted to grow from 82.8 years to 85.8 years in 2040.

So, what does this mean for society at large? Simple: There are going to be more and more people around the world living into old age. The National Institute on Aging projects that, globally, the 85-and-over population will grow 351% by 2050.

Ultimately, that means we may be looking at another major shift in human longevity—from an era when living with grandparents first became commonplace, to an era when living with great-grandparents becomes the new norm.

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