The term life expectancy means the average lifespan of an entire population, taking into account all mortality figures for that specific group of people. Life span is a measure of the actual length of an individual’s life.
While both terms seem straightforward, a lack of historical artifacts and records have made it challenging for researchers to determine how life spans have evolved throughout history.The Definition of Life Span
The Life Span of Early Man
Until fairly recently, little information existed about how long prehistoric people lived. Having access to too few fossilized human remains made it difficult for historians to estimate the demographics of any population.
Anthropology professors Rachel Caspari and Sang-Hee Lee, of Central Michigan University and the University of California at Riverside, respectively, chose instead to analyze the relative ages of skeletons found in archeological digs in eastern and southern Africa, Europe, and elsewhere.1
After comparing the proportion of those who died young with those who died at an older age, the team concluded that longevity only began to significantly increase—that is, past the age of 30 or so—about 30,000 years ago, which is quite late in the span of human evolution.
In an article published in 2011 in Scientific American, Caspari calls the shift the “evolution of grandparents,” as it marks the first time in human history that three generations might have co-existed.2
Ancient Through Pre-Industrial Times
Life expectancy estimates that describe the population as a whole also suffer from a lack of reliable evidence gathered from these periods.
In a 2010 article published in the Proceedings of the National Academy of Sciences, gerontologist and evolutionary biologist Caleb Finch describes the average life spans in ancient Greek and Roman times as short at approximately of 20 to 35 years, though he laments these numbers are based on “notoriously unrepresentative” graveyard epitaphs and samples.3
Moving forward along the historic timeline, Finch lists the challenges of deducing historic life spans and causes of death in this information vacuum.
As a kind of research compromise, he and other evolution experts suggest a reasonable comparison can be made with demographic data from pre-industrial Sweden (mid-18th century) and certain contemporary, small, hunter-gatherer societies in countries like Venezuela and Brazil.3
Finch writes that judging by this data the main causes of death during these early centuries would most certainly have been infections, whether from infectious diseases or infected wounds resulting from accidents or fighting.3
Unhygienic living conditions and little access to effective medical care meant life expectancy was likely limited to about 35 years of age. That’s life expectancy at birth, a figure dramatically influenced by infant mortality—pegged at the time as high as 30%.
It does not mean that the average person living in 1200 A.D. died at the age of 35. Rather, for every child that died in infancy, another person might have lived to see their 70th birthday.
Early years up to the age of about 15 continued to be perilous, thanks to risks posed by disease, injuries, and accidents. People who survived this hazardous period of life could well make it into old age.
Other infectious diseases like cholera, tuberculosis, and smallpox would go on to limit longevity, but none on a scale quite as damaging of the bubonic plague in the 14th century. The Black Plague moved through Asia and Europe, and wiped out as much as a third of Europe’s population, temporarily shifting life expectancy downward.An Overview of Bubonic Plague
From the 1800s to Today
From the 1500s onward, till around the year 1800, life expectancy throughout Europe hovered between 30 and 40 years of age.
Since the early 1800s, Finch writes that life expectancy at birth has doubled in a period of only 10 or so generations. Improved health care, sanitation, immunizations, access to clean running water, and better nutrition are all credited with the massive increase.3
Though it’s hard to imagine, doctors only began regularly washing their hands before surgery in the mid-1800s. A better understanding of hygiene and the transmission of microbes has since contributed substantially to public health.
The disease was still common, however, and impacted life expectancy. Parasites, typhoid, and infections like rheumatic fever and scarlet fever were all common during the 1800s.The History of Surgery: A Timeline of Medicine
Even as recently as 1921, countries like Canada still had an infant mortality rate of about 10%, meaning 1 out of every 10 babies did not survive. According to Statistics Canada, this meant a life expectancy or average survival rate in that country that was higher at age 1 than at birth—a condition that persisted right until the early 1980s.4
Today most industrialized countries boast life expectancy figures of more than 75 years, according to comparisons compiled by the Central Intelligence Agency.5
In the Future
Some researchers have predicted that lifestyle factors like obesity will halt or even reverse the rise in life expectancy for the first time in modern history.
Epidemiologists and gerontologists such as S. Jay Olshanky warn that in the United States—where two-thirds of the population is overweight or obese—obesity and its complications, like diabetes, could very well reduce life expectancy at all ages in the first half of 21st century.6
In the meantime, rising life expectancy in the West brings both good and bad news—it’s nice to be living longer, but you are now more vulnerable to the types of illnesses that hit as you get older. These age-related diseases include coronary artery disease, certain cancers, diabetes, and dementia.
While they can affect quantity and quality of life, many of these conditions can be prevented or at least delayed through healthy lifestyle choices like following an anti-aging diet, maintaining a healthy weight, exercising regularly and keeping stress hormones like cortisol at bay.