The Long Ceiling
Measuring Life Expectancy
In the spring of 1967, a sociology graduate student from Harvard named Nancy Howell took a flight from Boston to Rome with her new husband, an anthropologist named Richard Lee. After a few days in Italy, they flew to Nairobi, where they met an academic friend of Richard's and visited the Hadza tribes living in the region. From there they flew to Johannesburg,where they loaded up on supplies and socialized with a few more researchers in the area. They purchased a truck and drove north to the newly independent country of Botswana, picking up supplies in its new capital, then traveling northwest toward the swampy oasis of the Okavango Delta, recently flooded by seasonal rains. They rented a postbox in the town of Maun, the last outpost that would contain modern amenities like convenience stores and petrol stations. From Maun, they drove about 150 miles west, on unpaved roads, to the small village of Nokaneng, on the western periphery of the Kalahari Desert.
By this point in their journey, it was July in the Southern Hemisphere, but the winter precipitation that had flooded the Okavango Delta was nowhere in sight at the edge of the Kalahari. The newlyweds created a staging ground in Nokaneng, leaving behind sufficient petrol for future travels, and then set out due west across the desert, toward the Namibian border. In the end, it took them eight hours to drive sixty miles through arid terrain.
It was a grueling voyage, and in a sense, it was also a journey back in time. At the end of their eight-hour pilgrimage lay one of few regions of the Kalahari with sufficient water to support small communities of human beings, thanks to the nine waterholes spread out across an otherwise barren, flat landscape roughly 100,000 square miles in size. This more hospitable stretch of the Kalahari was sometimes referred to as the Dobe region, after the name of one of its waterholes. Howell and Lee had made their arduous journey because the Dobe region was the home of the Kung people, a hunter-gatherer society that had been almost miraculously isolated from all the conventions and technology of modern life. The Kung had managed to survive the preceding bloody centuries with almost no contact with other African societies and their European colonizers. They were protected, as Howell would later observe, "by the simple fact that none of the stronger peoples of southern Africa wanted to take their territory away from them, or even share it."
Like many surviving hunter-gatherer societies around the world, the Kung people offered Western anthropologists a provocative hint of the ancestral environment that had shaped most of the evolutionary history of Homo sapiens, before the agricultural revolution first arrived roughly ten thousand years ago. Lee had already visited the Kung society several times before 1967 to study their social organization, their food production techniques, and their strategies for managing and sharing resources within the community. Lee's research had been instrumental in proposing a new way of thinking about hunter-gatherer communities, one that undermined the long-standing view, most famously captured in Thomas Hobbes's description of the "state of nature" as "solitary, poor, nasty, brutish and short." Observed up close, the Kung did not appear to be struggling to get by, as Hobbes had assumed, in an arduous existence on the edge of starvation. Despite the paucity of natural resources around them, they seemed instead to enjoy a remarkably high standard of living, working less than twenty hours a week to support their nutritional needs. Based on similar research conducted on hunter-gatherer cultures in the Pacific, the anthropologist Marshall Sahlins had recently proposed a term for this reimagined model of early human social organization: the "original affluent society." The Kung and their equivalent did not represent some impoverished past, woefully deprived of all the advancements of modern technology. Instead, Sahlins argued, "The world's most 'primitive' people have few possessions, but they are not poor." Measured by the usual conventions of Western civilization, the Kung did indeed appear to be primitive: they lacked transistor radios and washing machines and multinational corporations. But measured by more elemental standards-food, family, human connection, leisure-they seemed far more competitive with the industrialized world than conventional wisdom at the time had assumed.
It was another kind of measurement that had brought Nancy Howell halfway across the world to the Dobe region, perhaps the most elemental measure of a human life there is. The !Kung offered at least some meaningful evidence that could help determine if early human existence was indeed "solitary, poor, nasty, brutish, and short." But as a demographer, Howell was particularly interested in the last of Hobbes's adjectives. How short were their lives exactly, compared to those of humans living in technologically advanced societies? How likely were they to live long enough to see their grandchildren? How likely were they to suffer the loss of a child, or die during childbirth? Affluence, after all, can be measured in leisure time, calorie intake, personal liberty-but surely one of the most important measures of an allegedly affluent society is how much life-and how little death-you experience as a member of that society.
Over the course of their three-year stay, Howell and Lee generated endless stacks of data: tracking kinship relations, pregnancies, calories consumed. But for Howell the most tantalizing-and elusive-number was one that has been the cornerstone of demography for its entire existence as a science: life expectancy at birth.
The number was elusive for several reasons. The Kung kept no written records of their population histories; they had no census data to share with Howell, no mortality tables. Howell and Lee were only spending a few years among the !Kung, not nearly long enough to conduct a longitudinal study of the population, observing births and deaths over many decades. But the most confounding hurdle was the simple fact that the !Kung themselves had no idea how old they were, in part because their entire numerical system topped out at the number three. If you asked a member of the !Kung society what age they were, you got only blank stares. Age as a numerical concept simply didn't exist for them.
This was the challenge that Nancy Howell confronted as she and her husband set up camp in the Dobe in late July 1967. How do you compute life expectancy in a culture that doesn't bother to count years?
The practice of recording the ages of a given culture's population is almost as old as writing itself. Archaeological evidence suggests that as far back as the fourth millennium BCE the Babylonians regularly conducted a census-probably for taxation purposes-that registered both overall population size and the age of individual citizens, capturing the data on clay tablets. But the concept of life expectancy is a relatively modern invention. Census data is a matter of facts: this man is forty years old; this woman is fifty-five. Life expectancy, on the other hand, is something else altogether: a prediction of future events based not on sorcery or anecdote or guesswork but rather on the sturdier foundation of statistics.
The first calculations of life expectancy were inspired by an unlikely source: a British haberdasher by the named of John Graunt, who conducted an elaborate study of London mortality reports in the early 1660s entirely as a hobby, publishing his findings in a 1662 pamphlet titled Natural and Political Observations Mentioned in a following Index, and made upon the Bills of Mortality. The fact that Graunt had no formal training as a demographer shouldn't surprise us; neither demography nor the actuarial sciences existed as formal disciplines back then. Indeed, Graunt's pamphlet is widely considered the founding document of both fields. Statistics and probability were themselves in their infancy during this period. (The word statistics, in fact, wouldn't be coined for more than a century; in Graunt's time, it was known as political arithmetic.) It remains something of a mystery, though, why Graunt himself decided to take up the problem of calculating life expectancy. One motivation was clearly altruistic: Graunt suspected that a close analysis of the city's mortality reports might alert the authorities to outbreaks of bubonic plague, allowing them to establish quarantines and other crude public health interventions. Thanks to this idea, Graunt is also considered one of the founders of epidemiology, though his pamphlet did little to arrest the devastating plague that erupted three years later in 1665, famously recounted in Samuel Pepys's diary and in Daniel Defoe's semifictional A Journal of the Plague Year.
While Graunt had been trained as a haberdasher, by the time he took up his amateur interest in demography, he had become a successful and well-connected businessman, serving as an officer in an international trading firm known as the The Drapers' Company. He served on several city councils and socialized with Pepys as well as with a polymath surgeon and musician named William Petty, who would go on to write a number of influential books on political economy and statistics, including one called Political Arithmetic. (A small subset of scholars of this period actually believe that Petty wrote the Natural and Political Observations of the Bills of Mortality, and not Graunt.) In the introduction, Graunt claims the original idea for the project occurred to him after many years of observing the way Londoners read the Bills of Mortality, the weekly catalog of citywide deaths that had been dutifully compiled and published by a guild of parish clerks since the early 1600s. The readers, Graunt observed, "made little other use of them, than to look at the foot, how the Burials increased, or decreased; and, among the Casualties, what had happened rare, and extraordinary in the week current: so as they might take the same as a Text to talk upon in the next Company." Londoners would scan the Bills for the headlines. (How many dead this week? Any interesting new diseases on the march?) If something caught their eye, they might pass the information off casually to a friend over a pint. But no one bothered to look at the Bills systemically, as data that might suggest a wider truth beyond the random fluctuations of each week's death toll.
Graunt's work proposed a radical break from that history of neglect. He would use the data not as fodder for idle gossip but as a way of testing hypotheses about the overall health of London's population, and as a way of perceiving long-term trends in that community. His investigation began with an informal perusal of a handful of Bills of Mortality, which suggested a few "Conceits, Opinions, and Conjectures"-as Graunt would later put it-about the city's health. Inspired by that initial set of queries, he spent months visiting Parish Clerks Hall on Brode Lane, just north of Southwark Bridge, acquiring as many Bills of Mortality as he could for his research. After a painstaking tabulation of the data-assembled centuries before the invention of calculators, much less spreadsheets-Graunt produced about a dozen tables that formed the centerpiece of his pamphlet. He began with one of the core questions of modern epidemiology: What was the distribution of causes of death in the population? To answer this question, he drew up two tables, one displaying "Notorious Diseases" and the other "Casualties." Both tables echo the famous "Chinese encyclopedia" from Jorge Luis Borges, with an eclectic mix of categories that seems comical to the modern eye. The "Notorious Diseases" table reads as follows:
The "Casualties" table featured a number of culprits that would be familiar to a contemporary demographer-he counted 86 murders, for instance-while other causes of death might raise an eyebrow: Graunt reported that 279 people in his survey died of "grief," while 26 were "frighted" to death.
The most crucial tabulations, however, involved what Graunt called the "acute and epidemical diseases": smallpox, plague, measles, and tuberculosis, which Graunt called consumption, using the terminology of the day. Calculating the total number of deaths over the period, and then breaking down that total into its component parts, allowed Graunt-for the first time-to propose an answer to the question, How likely were you to die from a particular cause? The Bills of Mortality were simply an inventory of deaths, facts without meaning beyond the individual, human tragedy of the life lost. Graunt's tables took the facts and transformed them into probabilities, which gave the authorities an actionable overview of what the major threats to public health were, insights that would allow them to combat those threats and prioritize between them more effectively.
But the most revolutionary statistical technique that Graunt introduced appeared in a chapter titled "Of the Number of Inhabitants." Graunt began the chapter referencing multiple conversations he had conducted with "men of great experience in this city" who suggested that the total population of the city must be in the millions. Graunt correctly perceived from his study of the mortality reports that the figure must be greatly exaggerated. (A city of 2 million people would have had far more deaths than were recorded in the Bills.) Through a number of roundabout calculations, Graunt proposed a much lower number: 384,000. Graunt himself thought the number had been determined "perhaps too much at random," but the calculation has held up well since he first published it: modern historians estimate London's population during this period to have been somewhere in the range of 400,000.
Armed with this crucial denominator-total population-Graunt was then able to examine another key element of the Bills of Mortality in a new light: age at death. He divided the overall pool of recorded deaths into nine separate tranches: those that died before their sixth birthday; those that died between their sixth and sixteenth birthdays; between their sixteenth and twenty-sixth birthday; and so on all the way up to eighty-six. With the deaths segmented in this fashion, Graunt was able to calculate the distribution of deaths in the population by age. For every hundred Londoners born, Graunt reported, thirty-six of them would die before their sixth birthday. In modern terminology, we would call that a childhood mortality rate of 36 percent.
The entirety of Graunt's "life table" was sobering. Less than half of London's population survived past adolescence; fewer than 6 percent made it to their sixties. Graunt did not manage to take the next step and reduce his life table to the single number we now use as perhaps the most fundamental measure of public health: life expectancy at birth. But we can calculate it based on the data Graunt did assemble in the table. By Graunt's account, the life expectancy of a child born in London in the mid-1660s was only seventeen and a half years.
When Nancy Howell arrived in the Dobe region in the middle of 1967 and began her investigation into the health and life spans of the Kung people, she possessed several crucial advantages over John Graunt in attempting such a study. She had three hundred years of advances in statistics and demography at her disposal. Since Graunt's time, demographers had developed extensive tools to calculate not only life expectancy at birth, but also, crucially, life expectancy at other ages as well. Howell had more than just conceptual tools, however. She had data entry systems and calculators to crunch the numbers; she had cameras to photograph the !Kung to help identify them for the records and connect them to studies that had been completed earlier in the decade. She had tape recorders to capture her interviews with the Kung. She would even ultimately develop a software program-called AMBUSH-to simulate the fluctuations in the !Kung population over time.