Friday, December 31, 2010

What the Roman Empire's demographics were like and what they mean

Vaclav Smil is a writer and researcher who occupies an enviable niche with his studies the interactions between human beings, the societies they create, and the natural environments that they inhabit, aiming to determine things like the factors influencing the sustainability of human civilization. One of his more recent books, this year's Why America Is Not A New Rome, was written with the aim of taking apart the myth that the United States is a new Roman Empire, complete with decadence and empire and ultimate collapse. This analogy works, I grant you, except for the many, many ways in which 21st century America and the 2nd century Roman Empire are fundamentally different. The United States is much more technologically and socially innovative than Rome ever was; by all accounts, Americans behave more realistically with regards to the wider world, and are certainly less prone to inhumanity; and at every level, most unlike Rome, the United States is part of a highly complex and globally integrated economy.

One chapter of particular interest to Demography Matters readers is his fourth, the simply-titled "Life, Death, Wealth." For students of demographics, the biggest problem with studying the populations of the classical era lies in the lack of data. What we know about the populations of the Roman Empire (and there were numerous distinctive regional populations, thanks to deep-seated environmental, cultural, and technological differences between Rome's provinces, as opposed to a single Roman Empire population) is a combination of careful analysis of surviving documents, archeological studies, and analogies with modern societies. Rome, Smil points out, was a society trapped in the first stage of the demographic transition, with very high fertility rates largely counterbalanced by very high death rates. Walter Scheidel's papers on classical demography go into detail on specific areas of the classical world; Wikipedia's article on classical demography provides a useful overview; Wikipedia user G.W.'s detailed primer goes into much greater, and gorier, detail.

Inhabitants of the Roman Empire had a life expectancy at birth of about twenty-five years. Although the figure relies more on conjecture than ancient evidence, which is sparse and of dubious quality, it is a point of general consensus among historians of the period. It originates in cross-country comparison: given the known social and economic conditions of the Roman Empire, we should expect a life expectancy near the lower bound of known pre-modern populations. Roman demography bears comparison to available data for early twentieth-century India and rural China, where life expectancies at birth were also in the low twenties.

About 300 census returns filed in Egypt in the first three centuries CE survive. R. Bagnall and B. Frier have used them to build female and male age distributions, which show life expectancies at birth of between twenty-two and twenty-five years, results broadly consistent with model life tables. Other sources used for population reconstructions include cemetery skeletons, Roman tombstones in North Africa, and an annuities table known as "Ulpian's life table". The basis and interpretation of these sources is disputed: the skeletons cannot be firmly dated, the tombstones show non-representative sample populations, and the sources of "Ulpian's life table" are unknown. Nonetheless, because they converge with low Roman elite survival rates shown in the literary sources, and because their evidence is consistent with data from populations with comparably high mortality rates, like eighteenth-century France, and early twentieth-century China, India, and Egypt, they reinforce the basic assumption of Roman demography: that life expectancies at birth were in the low twenties.

As no population for which accurate observations survive has such a low life expectancy, model life tables must be used to understand this population's age demography. These models, based on historical data, describe 'typical' populations at different levels of mortality. For his demographic synopsis of the Roman Empire, Bruce Frier used the Model West framework, as it is "the most generalized and widely applicable". Because it is based on only one empirical input, the model life table can provide only a very approximate picture of Roman demography. On two important points, the table may seriously misrepresent the Roman situation: the structural relationship between juvenile and adult mortality, and the relative mortality rates across the sexes. In any case, Roman mortality should be expected to have varied greatly across times, places, and perhaps classes. A variation of ten years would not have been unusual. A life expectancy range of between twenty and thirty years is therefore plausible, though it may have been exceeded in either direction in marginal regions (e.g., malarious urban districts on one end; high-altitude, low-density settlements on the other).

The specifics of any ancient age distribution, moreover, would have seen heavy variation under the impact of local conditions. In pre-modern societies, the major cause of death was not the chronic, end-of-life conditions that characterize mortality in industrialized societies, nor primary malnutrition, but acute infectious disease, which has varied effects on age distributions in populations. Pulmonary tuberculosis, for example, characterized much of the Roman region in antiquity; its deaths tend to be concentrated in the early twenties, where model life tables show a mortality trough. Similarly, in pre-modern societies for which evidence is available, such as early modern England and early eighteenth-century China, infant mortality varies independently of adult mortality, to the extent that equal life expectancies at age twenty can be obtained in societies with infant mortality rates of 15% to 35% (life table models omit this; they depend on the assumption that age-specific mortality ratios co-vary in uniform, predictable ratios). No ancient evidence can gauge this effect (there is a strong tendency to overlook infant death in the sources), and the model life tables may overstate it, but comparative evidence suggests that it is very high: mortality was strongly concentrated in the first years of life.

Smil notes, quite rightly, that the classical demographic pattern has no parallels in our contemporary world.

Today an analogue of these Roman values exists only in terms of continuing high birth rates and total fertility rates in Western, Eastern, and Central Africa; in 2007 these regions had average birth rates of, respectively, 42, 41, and 46/1,000, and average total fertilities of their countries ranged between 5.5 and 6.4. But even in these sub-Saharan countries, where the demographic transition has yet to run its full course, death rates have been already reduced quite significantly, to between 5 and 17/1,000, still nearly twice the current global mean of 9/1,000 but only about 35%-40% of the high Roman value (123).

[. . .] There is no modern population--even among the worst-off countries of sub-Saharan Africa--whose growth, longevity, and age structure would even remotely resemble the ancient Roman pattern. Perhaps the best contemporary analogy would be to imagine a population that is even more destitute and desperate than those of Sierra Leone or [Burkina] Faso and then to contrast it with the long-lived, formerly fast growing and now rapidly aging U.S. population, whose mean life expectancy at
birth is more than three times as high as the Roman Empire's (126).

Taking a look at a list of the world's countries by life expectancies, the only countries that come close to the likely life expectancy of the average Roman are a long list of terribly poor countries, all but Afghanistan located in sub-Saharan Africa, most with very high levels of HIV infection in addition to any number of other illnesses. But even the worst-off country, Swaziland, comes at 39.6 years at least a decade ahead of the Roman average and on par with the luckiest Roman districts. Combine this with the very high disease load of the average Roman and sustained undernourishment--Smil cites evidence suggesting that, at least as measured by average height, the food supply improved after the Roman Empire's collapse in the west--and the picture of a congenitally unhealthy ppopulation is inescapable. Combine that with the abundant evidence for the exceptionally unequal distribution of wealth and power within the Roman Empire, and with the significantly lower level of economic output (estimated by Smil to be inferior to that of central Africa and, of course, lacking the imported technologies available to central Africans) and you have a Rome that stands few comparison with even the worst-off countries of our 21st century world.

Wikipedia's G.W. pointed out that--to say the least--mortality and illness on this scale hampers economic growth.

Mortality on this scale discourages investment in human capital, hindering productivity growth (adolescent mortality rates in Rome were two-thirds higher than in early modern Britain); it creates large numbers of dependent widows and orphans; and it hinders long-term economic planning. With the prevalence of debilitating diseases, the number of effective working years was even worse: health-adjusted life expectancy (HALE), the number of years lived in good health, varies from life expectancy by no more than eight percent in modern societies; in high-mortality societies such as Rome, it could be as much as one-sixth beneath total life expectancy. A HALE of less than twenty years would have left the empire with very depressed levels of economic productivity.

It's difficult to avoid concluding that death and suffering on this scale had an effect on the cultures of the time. Smil remarks that, even though Romans accepted the fundamental humanity of slaves, Roman slaveowners--like their counterparts in the Atlantic slave/sugar economy more than a millennium later, in pre-revolutionary Haiti say--were still quite willing to treat their human property quite inhumanely (137-138). This habituation to extreme suffering, this coarsening of human sensibilities, isn't the sort of mindset that would support the sorts of rational, non-zero-sum social and political bargains that created the institutions undergirding the 21st century world.

Demographic patterns not too far removed from the Roman Empire's are normal for human beings, almost 95% of whom lived on Earth before it broke from the established demographic patterns in the 20th century. Even in favoured long-prosperous Canada, they prevailed within a century of my birth.

Originally uploaded by etherflyer

(This photo of a late 19th century Torontonian child's grave was taken by a friend of mine, and used here and in another blog post of mine; he's since taken others.)

We at Demography Matters are concerned with seeing where established trends will take us. Tonight, a day before the new year, I thought I'd take a look back to see where we escaped. It's worth gauging the distances between then and now, I think.


Eric Tolle said...

I think the most telling bit of information in this article is not the demographics of the Roman Empire, but the fact that the demographics are not far off from most societies throughout history. In other words, it's not that the Roman empire was uniquely horrifying in it's demographics, but that the modern world has drastically improved when it comes to quality of life.

Luci Sandor said...

Only the average will rarely be enough to describe a set of data.
This month, the BBC ran a documentary about the archaeological works in Italy's South, purportedly showing that Romans lived decently long lives once they passed the critical age of childhood diseases. Those were 'metropolitan' Romans, unlike some of the ones the book refers to (Egyptians, e.g.)
I think there is a difference between an uniform 100% death likelihood at the age of 20, and a 20% likelihood of life to sixties in a population where everybody else dies at 10. Although they both have an average life expectancy (presuming invariability over cohorts), in the latter case, our theoretical Romans might not discard as easily the chance of living a long life.

On a separate issue, I don't see how one can say that Romans were less inventive than Americans. You can't just count the innovations of a civilization. They were not cool, as in "they didn't have ipads" and such, but I am sure they had their merits. It is easy to fall on the trap of the "accelerating world", but I am sure the Western world gained momentum 200 years ago too.

Борис Денисов said...

Romans lived decently long lives once they passed the critical age of childhood diseases

At that level of mortality it is natural to have life expectance at age twenty same or higher as at birth