Every year in the course I teach about the 14th-century Black Death, I ask college students to imagine themselves as farmers, nuns, or nobles in the Middle Ages. What would their lives be like in the face of this terrible disease that has killed millions of people in just a few years?
Leaving aside what they think it would be like to face the plague, these undergraduates generally think that they would already be considered middle-aged or 20 years old during the medieval period. Instead of being in the prime of life, I think they will soon wear out and die.
These reflect the common misconception that human longevity is very recent and that no one in the past lived beyond their 30s.
But this is not true. I’m a bioarchaeologist, which means I study human skeletons unearthed from archaeological sites to understand what life was like in the past. I am particularly interested in demographics – mortality (deaths), fertility (births), and migration – and how this relates to health conditions and diseases, such as the Black Death, hundreds or thousands of years ago. There is physical evidence that many people in the past lived as long as some do today.
Bones record length of life
In the past, one of the first steps in demographic research was to estimate how old people were when they died. Bioarchaeologists do this by using information about how your bones and teeth change as you age.
For example, I look for changes in the pelvic joints that are common in older age. Observation of these joints in people whose ages we know today allows us to estimate the ages of people with similar-looking joints in archaeological sites.
Another way to estimate age is to count the annual addition of a mineralized tissue called cementum to teeth using a microscope. This is like counting the rings of a tree to find out how many years it has lived. Many studies using approaches like this have documented the existence of long-lived humans in the past.
For example, anthropologist Meggan Bullock and her colleagues examined skeletal remains and found that most people who reached adulthood in Cholula, Mexico, between 900 and 1531 were over 50 years old.
And of course, there are many examples in the historical record of people who lived very long lives in the past. For example, sixth-century Roman Emperor Justinian I reportedly died at the age of 83.
Analysis of ancient anatomically modern tooth development homo sapiens An individual from Morocco suggests that our species has had a long lifespan for at least the last 160,000 years.
Correcting a math misunderstanding
Given the physical and historical evidence that many people in the past had long lives, why does the misconception that everyone dies by the time they are 30 or 40 persist? It arises from confusion about the difference between individual lifespans and life expectancy.
Life expectancy is the average number of years of life remaining for people of a given age. For example, life expectancy at birth (age 0) is the average life expectancy of newborns. Life expectancy at age 25 is how long people live on average, given that they survive until age 25.
In medieval England, life expectancy at birth for boys born to landed families was only 31.3 years. However, in medieval England, life expectancy at age 25 for landowners was 25.7 years. This means that people celebrating their 25th birthday at that time could expect to live to the average age of 50.7, or another 25.7 years. While 50 may not seem old by today’s standards, keep in mind that it’s an average; many people would live much longer, into their 70s, 80s or even older.
Life expectancy is a population-level statistic that reflects the circumstances and experiences of a wide range of people, with very different health conditions and behaviors, some dying at very young ages, some living to over 100 years of age, and many whose lives are very different. The openings fall somewhere in between. Life expectancy is not a promise (or a threat!) about anyone’s lifespan.
What some people don’t realize is that low life expectancy at birth for any population generally reflects very high infant mortality rates. This is a measure of deaths in the first year of life. Given that life expectancies reflect averages for a population, large numbers of deaths at very young ages will bias calculations of life expectancy at birth towards younger ages. But typically, many people in these populations who survive the vulnerable years of infancy and early childhood can expect to live relatively long lives.
Advances in modern sanitation and vaccines that reduce the spread of diarrheal diseases, the leading cause of death for infants, can greatly increase life expectancies.
Consider the impact of infant mortality on overall age patterns in two contemporary populations with dramatically different life expectancies at birth.
Life expectancy at birth in Afghanistan is low at just over 53 years and the infant mortality rate is high; There are almost 105 deaths for every 1000 children born.
Life expectancy at birth in Singapore is much higher at over 86 years and the infant mortality rate is very low; Less than two babies die per 1,000 people born. In both countries, people survive to very old ages. But because so many more people die too young in Afghanistan, proportionally fewer people survive to old age.
Living a long life has long been possible
It is a mistake to see long lives as a remarkable and unique feature of the “modern” age.
Knowing that people often had long lives in the past can help you connect more with the past. For example, you can imagine multigenerational homes and gatherings in Neolithic China or Medieval England where grandparents bounced their grandchildren on their knees and told them stories about their own childhoods decades earlier. You may have more in common with people who lived long ago than you think.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Sharon DeWitte, University of South Carolina
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Sharon DeWitte receives funding from the National Science Foundation.