Plagues and Peoples

by William H. McNeill

  1300–1399 18 epidemics mentioned

  1400–1499 19

  1500–1599 41

  1600–1699 37 (an age of political disorder)

  1700–1799 38

  1800–1899 40

  Unfortunately one cannot conclude that the number of pestilences increased as suddenly as this table suggests, since records from the earlier times are more fragmentary than from recent centuries. All the same, the apparent doubling of recorded instances of epidemic disease in the sixteenth century probably corresponds to a real increase in the frequency with which epidemics arrived in China. China’s political system was then in good order, so that wars and rebellions cannot account for the disease record. New contacts arising from European transoceanic voyaging seem a far more plausible cause. If so, we can safely assume that an epidemiological basis was being laid in China after 1500 for the pattern of population growth that became such a prominent feature of subsequent Chinese history. The best available estimates for China’s total population are as follows53:

  1400 65 million

  1600 150 million

  1700 150 million

  1794 313 million

  The setback to China’s population growth apparent between 1600 and 1700 corresponds to the slowing of western Europe’s population growth in the same period. Colder winters and shortened growing seasons probably played a part in keeping Chinese population almost steady during the seventeenth century. A graph of temperatures, based on the frequency with which the Yangtze lakes froze over in wintertime, shows the coldest time in all recorded history to have fallen in the middle decades of the seventeenth century, precisely at the time when disorders incident to the displacement of the Ming by the Manchu Dynasty were at their peak.54 Such a coincidence of cold weather and civil disorder offers an obvious and adequate explanation for the cessation of China’s population growth in the seventeenth century. But only a changing disease regime, reflecting the increasing homogenization of infections around the world, seems adequate to explain the systematic population growth before and after the seventeenth-century halt.

  China’s modern demography and disease experience therefore seems to correspond to that of Europe. Japan’s population curve stands sharply in contrast. After rather rapid growth in the four centuries before 1726, when the first reasonably accurate census becomes available, Japanese population remained nearly constant until the middle of the 19th century. Estimates are as follows55:

  1185–1333 9.75 million

  1572–1591 18.0 million

  1726 26.5 million

  1852 27.2 million

  Widespread infanticide is believed responsible for this stabilization of population. But disease may have played a part in what happened, for the number of recorded epidemics, as compiled by Fujikawa Yu, also showed a notable increase after 1700, when the leveling off of population growth occurred.56

  No worthwhile estimates for Indian or Middle Eastern demographic history can be made on the basis of existing scholarship. Ottoman population history probably paralleled developments in other parts of the Mediterranean; and some bold demographers have suggested that the number of India’s inhabitants increased with the establishment of a more perfect internal peace in the second half of the seventeenth century, following the Mughal conquest of most of the peninsula, 1526–1605.57

  What exact course infectious disease may have followed in India and inner Asia remains unascertainable; but inasmuch as Indian ports shared on the intensified trade network that European ships extended across the world’s oceans, an intensified disease circulation surely must have existed in India also. Thus, despite gross lacunae in the evidence, nothing obstructs the inference that the modern disease pattern also established itself among civilized populations of Asia, perhaps less uniformly and more slowly than in Europe; but in parallel, indeed identical, fashion all the same.

  Diseases, however, were not the only biologically significant items that diffused more uniformly throughout the civilized world as a result of intensified transoceanic voyaging. Food crops did the same; and wherever a strange new plant offered some sort of value—including initially often merely the value of novelty—it was cherished and introduced into gardens and fields.

  By far the most important new food crops came from the Americas. Maize, potatoes, tomatoes, chili peppers, peanuts, and manioc all became available in Eurasia and Africa only after Columbus’ discovery of America. In many regions of the Old World, one or another of these crops was capable of producing far more calories per acre than anything known before. Older ceilings on population rose correspondingly wherever the new crops became generally cultivated. China, Africa, and Europe all were profoundly affected.58

  American food crops were important not solely for the increased calorie production per cultivated acre they permitted. Chili peppers and tomatoes, for instance, supplied a rich vitamin source whose importance in the diets of Mediterranean and Indian populations in modern times is very great indeed. How rapidly these American novelties became commonly available to supplement earlier and sometimes vitamin-deficient diets is unclear, though the first introduction of the new plants dates to the sixteenth century. As these foods entered into widespread use among rich and poor alike, one can be sure that a more adequate diet became available to the Indian and Mediterranean peoples, and health levels presumably reflected this fact.59 Oranges, originally cultivated in China, and other citrus fruits were also diffused widely by Europeans, even before the sovereign value of their juices against shipboard scurvy became widely known. But exactly when and where consumption of citrus fruits assumed dietary significance is impossible to say.

  Obviously enough, without the capacity to produce additional quantities of food, the population growth that set in toward the end of the seventeenth century in so many parts of the civilized world could not have gone very far. The superior productivity and nutritiousness of American food crops was therefore of the greatest importance for human life in every part of the Old World.

  Changes in disease patterns and the increase in productivity that the spread of American food crops permitted were probably the two most active factors in triggering civilized population growth in early modern times. They operated worldwide, and in parallel fashion to allow more human beings to survive and grow to maturity than had ever been possible before. There was, however, another significant change, this time on the macroparasitic side. Governments became fewer and more capable of maintaining domestic peace over broader regions of the earth, thanks to the global diffusion of a new weapon: the cannon. Cannon spread just as disease germs and plants did—along the world’s seaways. Everywhere that the big guns established themselves, the effect was to concentrate overwhelming force in fewer hands. Cannon were expensive, requiring large amounts of metal for their manufacture and rare skills for their management. Yet when the technique was new, a simple big gun brought into position against a defended place was capable within a few hours of blasting a hole even in the stoutest fortification.

  Such sovereign power to penetrate otherwise redoubtable strongholds radically diminished the military power of local potentates. Whoever possessed a few of the new weapons or commanded the skills needed for manufacturing them on the spot, was in a position to enforce his will much more effectively and overpoweringly than ever before. The result, naturally, was the consolidation of a relatively small number of “gunpowder empires.” Thus the late Ming and Manchu empires of China, together with the Mughal, Tokugawa, Safavid, Ottoman, Muscovite, Spanish, and Portuguese empires all may be classed as imperial states held together by a monopoly of decisive force exercised by a few cannoneers in the employ of the respective imperial governments. The territorial expansion of these states and the predictability with which imperial cannoneers could batter down the defending walls of local rivals meant that most of Asia and much of Europe began to enjoy a superior level of public peace from the latter part of the seventeenth century when these empires all came to be firmly established. War an
d plunder diminished their scope accordingly, being more and more brought under bureaucratic control, and directed toward distant and often thinly populated frontiers.60

  Such a general change in macroparasitic patterns had not occurred in human history since the end of the second millennium B.C., when the dawn of the Iron Age made weapons (and tools) vastly cheaper than before, and thereby increased the devastation men could wreak upon their fellows. Some twenty-five hundred years later the invention of cannon made weaponry more expensive. The new technology therefore acted in the opposite way, directing organized violence into narrower channels so that fewer human beings died in war or from its consequences despite the enhanced killing power well-equipped armies could exert in battle and siege.

  Taxes to support the new armament were heavy. Collection probably became more regular in parts of Asia and Europe, as bureaucratic structures of government consolidated their hold on supreme armed force thanks to the new power cannon could exert. But for peasants and artisans, regular taxation, even if hard to bear, was almost always less destructive than raiding and rapine of the sort that armed bands had resorted to for their support ever since barbarians carrying iron swords and shields had assaulted the citadels of Middle Eastern civilization after 1200 B.C. The symbiosis of cannon with a limited number of imperial bureaucracies must therefore be counted as a third global factor favoring the world-wide growth of civilized populations from the late seventeenth century until the present day.

  These three factors continue to affect the conditions of human life in the twentieth century. Indeed the world’s biosphere may be described as still reverberating to the series of shocks inaugurated by the new permeability of ocean barriers that resulted from the manifold movement of ships across the high seas after 1492. Yet almost as soon as the initial and most drastic readjustments of the new pattern of transoceanic movements had subsided, other factors—scientific and technological for the most part—inaugurated still further and almost equally drastic changes in the world’s biological and human balance. To survey them will be the task of our next chapter.

  VI

  The Ecological Impact of Medical Science and Organization Since 1700

  H

  itherto in seeking to understand the changing patterns of disease and its importance for human history as a whole, there has been little occasion to mention the practice of medicine. Undoubtedly folkways that reduced exposure to disease were as old as human society and language; and various customs, justified on other grounds, also had important epidemiological consequences—often of a positive kind. Thus, as we saw in Chapter IV, nomads of Manchuria diminished their exposure to plague on the basis of a theory that departed ancestors might be reincarnated as marmots. As such, these animals, which sometimes harbored the plague bacillus, had to be treated with special care.1 Another modern folk practice helped to protect the health of Tamil laborers brought from southern India to work on plantations in Malaya. They conformed to a custom that required them to bring water into their houses only once a day, and not to store it between times. This, of course, deprived mosquitoes of a breeding place indoors. As a result, Chinese as well as native Malays, who lived and worked under similar conditions but did not observe the Tamil custom, suffered distinctly higher rates of infection from dengue fever and malaria.2

  In numberless circumstances, such beliefs and rules of behavior must have helped to insulate human communities from disease chains. On the other hand, hygienic rules, especially when promulgated on the authority of divine revelation presumed to be universally applicable, sometimes had unfortunate side effects, as in the instance of the mosque in Yemen whose ablution pool harbored bilharzia parasites.3

  More generally, religious pilgrimages rivaled warfare in provoking epidemic infection. The doctrine that disease came from God could easily be interpreted to mean that it was impious to interfere with God’s purposes by trying to take conscious precaution against disease, either in war or on pilgrimage. Part of the meaning of pilgrimage was the taking of risks in pursuit of holiness. To die en route was, for the pious, an act of God whereby He deliberately translated the pilgrim from the hardships of life on earth into His presence. Disease and pilgrimage were thus psychologically as well as epidemiologically complementary. The same may be said of war, where risk of sudden death—one’s own or the enemy’s—was at the very core of the enterprise.

  Thus customs and beliefs tending to safeguard human communities from disease were matched by others that invited and provoked disease outbreaks. Until very recently, medical theories and treatments fitted into this tangle of contradictory practices smoothly enough. Some cures were helpful; some indifferent; some, like the practice of bleeding for fevers, must have been positively harmful to most patients. Like popular folkways, medical theories were crudely empirical and excessively dogmatic. Doctrines set forth in a few famous books were treated as authoritative: Galen and Avicenna for the European and Moslem world played this role, as Caraka did for the Indian; whereas in China, several authors shared canonical status. Experience was then interpreted in terms of theory, and cures inflicted accordingly.

  Overall, it is very doubtful whether the physiological benefits of even the most expert medical attention outweighed the harm done by some of the common forms of treatment. The practical basis of the medical profession rested on psychology. Everyone felt better when self-confident, expensive experts could be called in to handle a vital emergency. Doctors relieved others of the responsibility for deciding what to do. As such their role was strictly comparable to that of the priesthood, whose ministrations to the soul relieved anxieties parallel to those relieved by medical ministrations to the body.

  Yet there was a difference. Doctors dealt with things of this world- and as such their skills and ideas were more liable to empiric elaboration over time. Medical professionals in fact behaved in about the same way as humble folk did by cherishing responses to disease that by some happy chance seemed to achieve desired results. This relative openness to new departures was, perhaps, the most important quality of the medical professional prior to the spectacular breakthroughs of the past century or so. Even the august Galen was subject to emendation, though it was not before the seventeenth century that the theory of humors on which he had based his medical practice began to be widely questioned among European doctors. Among Asians, medical ideas and practices, once they achieved a classical definition, seem to have responded less coherently to novelty.4

  The organization of the profession in Europe around medical schools and hospitals may have been decisive in producing more systematic responses to new disease experiences. Hospitals gave opportunity for repeated observation of the symptoms and course of a disease. A cure that worked once could be tried again on the next patient, and professional colleagues were on hand to observe the result. Such colleagues stood ready to accord admiration and respect to the man whose cures worked better than usual; and a reputation for skill above the ordinary also meant swiftly rising income for the successful innovator. Under such circumstances, everything pushed the ambitious medical man toward empiric adventure, trying out new cures and watching to see the result. Moreover, the ancient Hippocratic tradition, emphasizing careful observation of disease symptoms, made such conduct professionally respectable. It is not, therefore, surprising that European doctors reacted to the disease novelties of 1200–1700 by altering major elements of older theory and practice. By contrast, Asian medical experts, who did not operate in hospital environments, met the disease experiences of these centuries by holding fast to ancient authorities—or claiming to do so even when something new crept in.

  To be sure, even in Europe almost a century passed before medical response to the emergency of plague achieved anything resembling a clear definition. But by the end of the fifteenth century, Italian doctors had worked out within the framework of city-state government a series of public health measures designed to quarantine plague, and if it came, to cope with the heavy die-offs such visitations
regularly brought. In the course of the sixteenth century these measures became both more elaborate and better administered. Preventive quarantines probably began to intercept chains of plague infection more and more often. Theories of contagion were advanced to justify quarantine, and notions originating from practical folk experience such as the belief that wool and textiles could carry plague—a belief vindicated by the behavior of hungry fleas that, having taken refuge in a bale of wool after their rat host had died, were liable to discover a much-wanted next meal by biting the arm of the man who unpacked the bale—at least achieved the dignity of being discussed in print.5

  European doctors reacted to the disease consequences of the discovery of America in much the same way as their predecessors had to the plague. Learned discussion of syphilis was as florid as the symptoms of the disease itself when new. Other novelties excited no less attention, and none of them fitted smoothly with ancient learning. The blow to reverence for the ancients was fundamental, and one from which traditional medical practice and education could never completely recover. As more and more details about America became avail- able, the inference that modern knowledge had, in some ways at least, surpassed the ancients became irresistible. Such views opened wider the door to medical innovation, and encouraged Paracelsus (1493–1541) to reject Galen’s authority entirely. New diseases like syphilis seemed to call for new and “stronger” medicines; and this became one of the stock arguments for resort to the Paracelsian chemical pharmacopeia and mystical medical philosophy.6 With every fundamental of medicine thus called into question, the only logical recourse was to observe results of cures administered in accordance with the old Galenic as against the new Paracelsian theories, and then to choose whichever worked better. The swift development of European medical practice to levels of skill exceeding all other civilized traditions resulted.