Plagues and Peoples

by William H. McNeill

  Nevertheless, before the eighteenth century the demographic impact of the profession of medicine remained negligible. Relatively few persons could afford to pay a doctor for his often very expensive services; and for every case in which the doctor’s attendance really made a difference between life and death, there were other instances in which even the best available professional services made little difference to the course of the disease, or actually hindered recovery. For this reason, mention of medical practice and its history in the earlier chapters of this book seemed unnecessary. Only with the eighteenth century did the situation begin to change; and it was not really until after 1850 or so that the practice of medicine and the organization of medical services began to make large-scale differences in human survival rates and population growth.

  Long before then, the new ecological balances among the world’s continents and civilizations that had begun to define themselves in the latter half of the seventeenth century became spectacularly evident. In particular, massive population growth in China and Europe assumed unexampled scale, thanks to the fact that both regions started from a higher initial population level than similar growth spurts of times past had ever done. After about 1650 Amerindian population figures began to bottom out in those regions where exposure to European and African diseases was of longest standing, and by the mid-eighteenth century Old World emigrants to America began to demonstrate remarkable rates of natural increase. Die-offs among formerly islanded populations continued (e.g., among natives of Oceania); but this phenomenon affected smaller numbers, since after the sixteenth century no really large human communities remained outside the disease-net European shipping had already woven across all the earth’s oceans and coastlines.7

  To be sure, even in the most intensely studied regions, population estimates for the seventeenth century are unsatisfactory, so that statistical demographers now prefer to begin making generalizations about 1750, rather than, as an earlier generation of experts had tried to do, retrojecting their estimates to 1650.8 But no one doubts that sometime between 1650 and 1750 (and recent opinion inclines toward the latter rather than the earlier date), a “vital revolution” took place in parts (though not in all) of Europe, manifesting itself in a more massive population growth than that continent had ever known before. The same was true in China, where the pacification brought by the new Manchu Dynasty after 1683 inaugurated a century of population growth during which Chinese numbers more than doubled, rising from about 150 million in 1700 to about 313 million in 1794.9

  By comparison, Europe’s population seems puny, reaching only a total of about 152 million by 1800.10 Moreover, the unparalleled spurt in Chinese population affected all parts of the country, whereas in Europe comparable growth rates were chiefly evident toward the margins—in the steppelands to the east and in Great Britain and America to the west. The core area of continental Europe continued to suffer periodic devastation by war and crop failure, so that any tendency toward massive population growth of the sort manifest in China was quite effectually masked until late in the eighteenth century.

  The relation between population growth and the intensification of industrial production which we have learned to call the Industrial Revolution, is a much debated point among historians, and especially among historians of England.11 That country witnessed extraordinary changes in both industry and population during the eighteenth century; and the two obviously supported each other, in the sense that new industry needed workers, and expanding population needed new means of livelihood. Minute study of English parish records has much to teach in these matters; but to understand the general process one must consider all of Europe and the transoceanic zones of colonization as an interacting whole. Such a perspective on European demography, 1650–1750, brackets the agricultural pioneering and population growth along the eastern frontier with the parallel process of pioneering taking place in colonial lands across the seas, above all in North America. The difference between migration overland and migration overseas was less significant than the basic identity of the process of opening up new agricultural land that was taking place simultaneously on both frontiers. The intensification of commercial industrial activity in the center, mainly in Great Britain, also requires this larger perspective, for it was as a focus of the enlarged Europe of the Old World and the New that the English Midlands and London developed the new commercial and industrial patterns—above all more extensive use of mechanically powered machinery—that we lump together as the industrial revolution. But even if one accepts this expanded definition and counts both wings of the colonial movement as part of Europe, it only adds about 8–10 million to the total for European populations in 1800.12 Hence the increase of European numbers remains far less massive than the Chinese expansion of the same period, being only about one fifth as great.

  Elsewhere in the civilized world there seems good reason to suppose that population changed little, one way or another, until after 1800. In India, extensive civil disorder broke out during the latter part of the reign of the Emperor Aurangzeb (1658–1707) and sporadic warfare continued thereafter until 1818. Indeed, in the Moslem world as a whole, none of the signs of an expanding population are discernible, and political disorder tended to increase as the morale and efficiency of both Ottoman and Safavid administrations, like that of the Mughals in India, diminished.

  Hence it appears that the Chinese eighteenth-century response to the altered ecological balances of the world was atypical. Parallel potentialities elsewhere were masked by a variety of countervailing circumstances. Only in China did public peace prevail unbroken and conventional limitations upon taxes and rents remain well defined, so that damaging or destructive macroparasitism remained rare. Simultaneously, increasingly frequent epidemics worked less and less demographic damage, as one disease after another verged toward the relatively harmless status of becoming an endemic childhood affliction. This opened wide the gate toward all the familiar features of the vital revolution: lessened adult mortality sustaining more completed families, whereupon a numerically reinforced generation, confronting the same situation, expanded the numbers of its children even more, etc.

  Snowballing population growth of course confronted the farmers of China with the task of wresting more food from the same landscape, since political and ecological obstacles prevented any very notable geographical expansion across Chinese frontiers. The imperial government prohibited overseas ventures in the 1430s and subsequent rulers maintained the ban, thus choking off any possibility of large-scale Chinese settlement in the Pacific coastlands of America, or in nearer lands like the Philippines or Malaya. From the time of the Manchu conquest in the 1640s, Chinese settlement in Manchuria and Mongolia was also prohibited, for the new rulers of China wished to maintain their ancestral lands and nomadic way of life unchanged. Only in the South could expansion of Chinese area of settlement continue; and even there local political resistance organized by the kingdoms of Annam and Burma, together with the epidemiological perils of monsoon forest environments, slowed Chinese pioneering to quite modest proportions.

  Nevertheless, within the broad circuit of lands already firmly incorporated into China’s landscape, it proved possible in the eighteenth century to find food enough to more than double previous levels of population. Increasingly intensive application of labor to the land did the trick, together with massive reliance on new crops, mainly American in origin—sweet potatoes, maize, peanuts in particular—that could be cultivated on land too steep or too dry for rice paddies.

  China’s circumstances, in other words, gave full scope to the new possibilities inherent in the changed disease regime, crop distribution and military technology resulting from the opening of the oceans to human movement. China, in fact, anticipated by more than a century similar responses among peasant masses in other parts of the world, who reacted similarly to new ecological balances in the nineteenth and twentieth centuries, wherever political pacification and the possibility of expanding agricultural pro
duction simultaneously presented themselves. China’s precocity in this respect may have been due in large part to the cultural traditions of the Middle Kingdom. Political unity came easier to a land accustomed from antiquity to regard imperial centralization as the only rightful form of government. And Confucian principles put high value upon family continuity from father to son. Such attitudes must have contributed to the early and dramatic expansion of China’s population; yet this does not mean that the altered role of diseases was not also of great importance in securing the actual result.

  Elsewhere, the potential for enhanced population growth presumably also existed among all the disease-experienced civilized communities of the world, but difficulties with expanding the food supply and/or suppressing destructive patterns of macroparasitism masked overt manifestations of the new possibilities until the nineteenth century. Only along frontiers of colonization, where civilized agricultural techniques impinged upon land previously thinly inhabited, did the same combination of circumstances as prevailed in most of China also unleash extraordinary population expansion before 1800.

  The two principal such regions were the Ukraine in Russia and the Adantic coast of the Americas. In the Ukraine, and Russia generally, risk of bubonic infection from ground-burrowing rodents remained a significant demographic factor throughout the eighteenth century. In 1771, for instance, plague in Moscow killed 56, 672 persons in a single season, according to official figures—a total not far short of that recorded in London during the famous plague years, 1664–6.13 Nevertheless, with each acre of land broken to the plow, the natural habitat available to ground-burrowing rodent communities diminished, and thereby the possibilities for transfer of infection from rodent to human populations was restricted. The plow could never banish plague, but it did undoubtedly reduce its dangers by slow, almost imperceptible degrees. The remarkable growth of Russian population in the eighteenth century, estimated at 12.5 million in 1724 and 21 million by 1796, attests the fact that an enlarged food supply quite overbalanced any disease losses incident to breaking in upon lands formerly occupied by infected rodents.14

  American settlers did not have to worry about bubonic infection. They did, however, confront special problems because of their semi-isolation from the main centers of European civilization and disease circulation. Smallpox, for instance, so destructive to Amerindians, often killed white settlers as well when they met infection only as adults because of their remoteness in childhood from a dependable focus of infection. For this reason, as we shall soon see, many Americans were willing to accept the risks inherent in deliberate inoculation with smallpox—a technique that became familiar to European doctors in the eighteenth century—whereas in the more thoroughly diseased communities of Europe, where only small children were likely to die of smallpox, such risks were unacceptable, and inoculation failed to win general ac ceptance until the nineteenth century, when better methods reduced the risk of mortal infection to negligible proportions.

  Ireland offers an interesting, territorially less impressive but demographically more dramatic, case of frontier expansion in the eighteenth century. After years of brutal war, the country was effectively pacified in 1652. Three distinct national groups—English, Scots, and Irish—thereafter confronted an almost empty island with diverse agricultural methods and economic expectations. In most of Ireland, it was the latter nationality that prevailed, despite profound political disadvantages. What made their success possible was an early acceptance of the potato as a staple crop—an acceptance made easier by the fact that the Irish had previously practiced agriculture on only a limited scale, and did not, like the English, depend on expensive plows and plow teams for tillage. Cheap and abundant potatoes allowed the Irish to live for less, and thereby to undercut English settlers systematically. Scots, whose techniques of cultivation and living standards were almost on a par with those of the Irish, managed to survive in Ulster. They, too, took to the potato as a staple after widespread failure of the grain crop early in the eighteenth century proved how valuable that previously despised root could be. Explosive Irish population growth got into high gear only toward the end of the eighteenth century, when, ironically enough, rising prices for grain in England made tillage profitable as never before for the Anglo-Irish landlords who ruled the island. This required labor; and the native Irish were available to provide it in return for an acre or so of land for a potato patch upon which an entire family could live—in abjective poverty perhaps, but in a reasonably good state of nutrition all the same.15

  While such remarkable swarmings of peasant populations as occurred in eighteenth-century Ireland and in China were, perhaps, symptomatic of things to come elsewhere in a later age, the population and disease history of Great Britain also assumed a special significance as the industrial revolution gathered headway in that island. Until the 1870s, when grain and other food supplies began to flood in from across the oceans, the growth of urban population in Britain required intensification of local food production. Improved farm machinery, fertilizers, crop rotations, seed selection, and methods of food storage and preservation, all played a part in making this possible. The most significant change was the abandonment of fallowing as a method for keeping down weeds. Crops such as turnips that required careful tillage during their growth seasons, allowed simultaneous destruction of weeds and production of a valuable crop. Agricultural productivity was thereby enhanced by almost a third.

  There was another unexpected consequence of this “new husbandry” that began to spread from its original foci on either side of the North Sea in the later seventeenth century. For turnips and alfalfa (the other important crop that replaced fallow) provided feed for cattle on a scale hitherto impossible in European agriculture; and the presence of larger numbers of cattle both improved human diet by expanding meat and dairy production, and simultaneously provided malaria-carrying anopheles mosquitoes with a preferred source of blood. Since the malarial plasmodium does not find cattle suitable hosts, mosquito preference for the blood of cattle had the effect of interrupting the chain of malarial transmission in those parts of Europe where the number of cattle increased sufficiently. Malaria thus gradually withdrew to the Mediterranean lands, where the new fodder crops could not be produced because of summer drought. Consequently, what had been a chronic and important disease among northern Europeans for centuries ceased to afflict regions where the new husbandry prevailed.16

  Other complex ecological results flowed from the spread of the new style of agriculture. More animals meant more meat and milk in human diet, and an enlarged supply of protein. This may well have increased human capacities to manufacture antibodies against infection of any and every kind, since such antibodies are themselves proteins and can only be produced from the chemical building blocks proteins supply. Generalized levels of resistance to infectious disease may therefore have risen significantly among wide segments of the population.

  Another possibility: enclosure of wasteland and of open fields, which proceeded rapidly in Britain in the eighteenth century, had the side effect of removing the incentive to overstock pastures, and segregated sheep and cattle into relatively small, privately owned populations. This almost certainly led to notable improvement in the health of flocks and herds. First of all, the animal got a better diet than had been possible when overstocking the common pasturelands was the only way for an individual villager to take maximum advantage of his rights. Secondly, chains of infection among the flocks and herds could often be interrupted. Previously, animals ran freely throughout the village common land, and made occasional contacts with animals from adjacent villages as well, since no fences divided the pastureland belonging to one community from the lands of its neighbors. Hence an infection could easily affect every animal in the village and for miles around. Such epizootics were far less likely to occur when fences and enclosed fields broke up the animals even of a single village into separate and mutually isolated groups. Such a change was important for human health, too, since
a good many animal infections—bovine tuberculosis and brucellosis, for instance—were readily transferable to humankind.17

  Diminution of such infections and the parallel decay of malaria changed the disease experience of England in far-reaching ways between 1650 and 1750. In France, where enclosure did not occur and the new husbandry hardly got started in the eighteenth century, peasant health remained miserable. Epidemics and chronic infections ravaged whole provinces; malaria and tuberculosis remained serious health problems; and a vaguer battery of other lethal infections—grippe, dysentery, pneumonia, and “military sweats”—continued to kill off a significant number of French peasants after 1775, when careful administrative records first become available.18 Inasmuch as English population growth far outstripped French in the eighteenth century, while both countries remained pre- dominantly agricultural, there is little doubt that the health of the countryside in England became noticeably better than what prevailed in France. Unfortunately, the absence of administrative records of disease incidence from Britain comparable to those French officials began to compile after 1775 makes direct comparison impossible.

  A major consequence of the improvement in rural health such as seems to have taken place in England in the century after 1650 was a notable increase in the efficiency of agricultural labor. Healthy people work better—and more regularly; and, as is obvious, losses to agricultural production resulting from inability to do necessary work at the right time of the year disappear in proportion as laborers cease to suffer from debilitating fevers and similar afflictions which tend to crest during the growing season. As health improved, fewer workers could therefore feed larger numbers of city folk. The urbanization of Great Britain, which was such a conspicuous feature of late eighteenth-century development, could not have taken the course it did under any other circumstances.