Plagues and Peoples (29 page)

By contrast, the nomads of the western steppelands, falling as they did under Moslem influence, may have accepted plague as irremediable. They also had to cope with a different rodent population than existed in the eastern steppe; and this may have made the development of suitably protective folkways more difficult. At any rate, it is clear that bubonic infections did continue to break out in eastern Europe at frequent intervals throughout modern times, down to and including the twentieth century. By way of contrast, the only recent plague outbreak in the Far East was, as we saw, the work of ignorant Chinese immigrants moving into an unfamiliar environment where they disregarded nomad customs that were quite adequate, if carefully observed, to protect the human populations from infection.

The disease disasters that probably decimated the people of the steppes in the thirteenth to fifteenth centuries were soon followed by two additional blows: first, the circumnavigation of Africa by European seamen (1499), followed by the systematic
opening up of a sea route between Europe and the other major centers of civilized population. Thereafter the caravans of the steppelands were no longer the cheapest way to carry Chinese goods to Europe and vice versa. One of the sustaining impulses for overland movement of goods thenceforth disappeared, and the basis for any economic revival on the steppes diminished accordingly. This was in turn followed in the seventeenth century by the development of effective hand guns that made the traditional archery of steppe cavalry ineffective against well-trained infantry. Partitioning of the Eurasian steppelands between adjacent agricultural empires swiftly and ineluctably followed, with Russia and China the principal beneficiaries.
⁷⁸

It is therefore tempting to suppose that the major consequence of the changed distribution of bubonic infection in Eurasia was the disembowelment of steppe society. There is small likelihood of ever being able to find documentary support for such a view. On the other hand, Chinese, Islamic, and perhaps even Indian documents, if they were to be carefully perused by linguistically competent scholars sensitive to the question, probably would provide a basis for reconstructing population and disease history of those societies with approximately the same degree of precision that obtains today with respect to Europe. But since the necessary painstaking labor has not even begun, general statements about the population history of Asian societies other than China before the eighteenth century lack any satisfactory basis. Even for China, study of local records will be needed to assess the importance of disease in cutting back China’s population by more than 50 per cent between 1200 and 1400.

Farther away from the new focus of infection in the steppes, human responses to the changed disease pattern probably weakened. In India, for instance, if that subcontinent was in fact one of the most ancient homes for chronic plague infection among communities of burrowing rodents, the changes wrought farther north by the Mongols would make little difference. The same is true of even more distant sub-Saharan
Africa. Habits and customs that restricted human plague to bearable proportions had presumably defined themselves in both these regions in ancient times, when plague first went aboard ships and began to spread through the Indian Ocean and adjacent seas. Consequently, any additional exposure to
Pasteurella pestis
that may have filtered down from the North, across the Egyptian land bridge or by some other route, would make little difference to the plague-experienced peoples of Africa and India. The fact that there seem no special signs of any population crisis in India in the fourteenth century is not therefore surprising; though the almost total absence of documentation really makes this, and any alternative speculation, almost pointless. Plague did exist in India and east Africa between 1200 and 1700. How serious it may have been, no one can say.

What we see, then, as the over-all response to the changed communications pattern created in the thirteenth century by the Mongols is a recapitulation of what we saw happening in the first Christian centuries. That is to say, massive epidemics and attendant military and political upheavals in Europe and (less clearly) also in China led both in the early Christian centuries and in the fourteenth century to sharp diminution of population in the Far East and in the Far West; but in the regions between, both epidemic history and population history are difficult or impossible to discern. In the earlier instance, several diseases were probably at work, and it took a longer time for population to recover, especially in Europe. In the fourteenth century, on the contrary, a single infection was probably responsible for most of Europe’s population decay, and recovery both in Europe and in China was swifter, so that by the second half of the fifteenth century unmistakable population growth again set in at each extreme of the Old World ecumene. Even in Muscovy and the Ottoman empire, lands lying close by the steppe focus of plague infection, population growth became unmistakable in the sixteenth century, perhaps beginning even earlier.
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Before the limits of that renewed growth had been attained,
a fresh disturbance to ecological and epidemiological world balances set in as a result of the discovery of the New World by Europeans. Consideration of the drastic and dramatic epidemiological consequences of this event will be the theme of the next chapter.

Transoceanic Exchanges, 1500–1700

I

n the preceding chapters, little has been said about the New World and its disease experience. Absence of written records and the limited results attained by medical study of skeletal remains from Amerindian archaeological sites make such lopsidedness inevitable. Nevertheless, in view of what happened after the Spaniards inaugurated free exchange of infections between the Old World and the New, it seems certain that Amerindian encounters with disease before Columbus had been unimportant from an epidemiological point of view. The inhabitants of the New World were bearers of no serious new infection transferable to the European and African populations that intruded upon their territory—unless, as some still think, syphilis was of Amerindian origin—whereas the abrupt confrontation with the long array of infections that European and African populations had encountered piecemeal across some four thousand years of civilized history provoked massive demographic disaster among Amerindians.

Reasons for this disbalance are not far to seek. The New World was, by comparison with the mass and ecological complexity
of the Old, no more than an enormous island. Forms of life were, in general, more highly evolved in Eurasia and Africa, having responded to a wider range of variability arising in the larger land mass. Consequently, plants and animals from the Old World introduced by Europeans to the Americas often displaced native American species, and disturbed preexisting ecological balances in explosive and, at least initially, highly unstable ways. We seldom realize, for instance, that Kentucky blue grass, dandelions, and daisies, so familiar in contemporary North American landscapes, are all of Old World origin. Similarly, runaway swine, cattle, and horses developed into vast wild herds in the New World with results that were sometimes destructive to the vegetable cover and soon led to serious erosion of topsoil.
¹
American food plants had far-reaching importance for the peoples of Europe, Asia, and Africa after 1500, but few organisms of American provenance were successful in competing in the wild with Old World life-forms—though some examples do exist, e.g., the spread of the plant louse,
phylloxera
, that nearly destroyed European vineyards in the 1880s.

The undeveloped level of Amerindian disease was, therefore, only one aspect of a more general biological vulnerability, but one that had peculiarly drastic consequences for human life. Precise information about disease in the Americas before Columbus is difficult to come by. Bone lesions can be found on pre-Columbian skeletons indicating some sort of infection. These have sometimes been interpreted as syphilitic by doctors seeking to confirm the American origins of that disease. But such identifications are controversial, since the way one micro-organism attacks a bone is very similar to the way another is likely to do so; and tissue reactions to such invasions are also similar, no matter what the infectious agent may be.
²
Unambiguous proof of the presence of intestinal worms and protozoa has been discovered at pre-Columbian burial sites, but even so the array of parasitic worms fell considerably short of varieties abounding in the Old World.
³

Indication of disease and epidemic death have been found
in Aztec codices; but these seem related to famine and crop failure and may not have been the result of the sort of human-to-human infectious chain that existed in the Old World. Moreover, disasters came far apart in time, only three being discernible in surviving texts.
⁴
After the Spanish conquest, old men even denied that disease had existed in any form in the days of their youth.
⁵
It looks, therefore, as though Amerindian communities suffered little from disease, even though in both Mexico and Peru, the size and density of settlement had reached far beyond the critical threshold at which contagious disease organisms could sustain a simple human-to-human chain of infection indefinitely. In this, as in some other respects, the Amerindian civilizations seem comparable to ancient Sumer and Egypt, rather than to the epidemiologically scarred and toughened communities of sixteenth-century Spain and Africa.

Several centuries—perhaps more than a thousand years—had passed since favored regions of Mexico and Peru had begun to carry human populations dense enough to sustain human-to-human disease chains indefinitely. Yet such infections do not seem to have established themselves. Presumably the reason was that the domesticable animals available to the Amerindians did not themselves carry herd infections of a sort that could transfer their parasitism to human populations when those populations became sufficiently large. This sort of transfer is what must have happened in the Old World, where massive herds of wild cattle and horses, dispersed across the steppe and forest lands of Eurasia, were sufficiently numerous and made close enough contact with one another in a wild state to be able to sustain infections that passed from animal to animal without any sort of intermediate host. By comparison, wild llamas and alpacas lived high in the Andes in small and dispersed groups. These were too few and too isolated to sustain such infections in the wild. There seems to be no plausible reconstruction of the style of life of the wild ancestors of the guinea pig—the other distinctive Amerindian domesticated animal. And as for dogs, mankind’s oldest domesticated
animal, though they today share many infections with humans, it is clear enough that in their wild state they, too, must have existed in relatively small and isolated packs. Thus with the possible exception of the guinea pig, the Amerindians’ domesticated species, like the human hunting bands that had initially penetrated the Americas, were incapable of supporting infectious chains of the sort characteristic of civilized diseases. No wonder, then, that once contact had been established, Amerindian populations of Mexico and Peru became the victims, on a mass scale, of the common childhood diseases of Europe and Africa.
⁶

The scope of the resultant disaster reflected the fact that both central Mexico and the heartlands of the Inca empire were very densely settled at the time of the European discovery of America. The two most important American food crops, maize and potatoes, were more productive of calories per acre than any Old World crops except rice. This allowed denser populations per square mile of cultivated ground in the Americas than was attainable anywhere in the Old World outside of the East Asian rice paddy region.

Moreover, Amerindian customary ways of preparing maize for food obviated some of the nutritional disadvantages of a diet in which that cereal plays the principal role. The kernels were soaked in a lime solution, which broke down some of the molecules of the maize in a way that allowed human digestion to synthesize needed vitamins that are absent from the maize itself. Without such treatment, a diet of maize leads to niacin deficiency. Symptoms of this deficiency, known as pellagra, were often seriously debilitating among European and African populations that took to maize cultivation. But Amerindians escaped pellagra by soaking maize to make “hominy grits,” and by supplementing their diet with beans in those regions where hunting was no longer possible because human populations had become too dense.
⁷

Ecological adjustment in Mexico and Peru showed signs of strain, even before the Spaniards arrived and upset everything so radically. In Mexico, erosion was already a serious problem;
and in some irrigated coastal areas of Peru, salting of the soil seems to have led to population collapse not long before Pizarro appeared.
⁸
Everything points to the conclusion that Amerindian populations were pressing hard against the limits set by available cultivable land in both Mexico and Peru when the Spaniards arrived. Moreover, the absence of any considerable number of domesticated animals meant that there was a smaller margin between the sum of agricultural productivity in the Americas and direct human consumption than was commonly the case in the Old World. In time of crop failure or other kind of food crisis, Eurasian flocks and herds constituted a sort of food bank. They could be slaughtered and eaten; and in times and places when overpopulation started to be felt, human beings always displace herds by turning pastureland into cropland—at least for a while. No such cushion existed in the Americas, where domesticated animals played a merely marginal part in human food patterns.

All these factors therefore conspired to make Amerindian populations radically vulnerable to the disease organisms Spaniards and, before long, also Africans, brought with them across the ocean. The magnitude of the resultant disaster has only recently become clear. Learned opinion before World War II systematically underestimated Amerindian populations, putting the total somewhere between eight and fourteen million at the time Columbus landed in Hispaniola.
⁹
Recent estimates, however, based on sampling of tribute lists, missionary reports and elaborate statistical arguments, have multiplied such earlier estimates tenfold and more, putting Amerindian population on the eve of the conquest at about one hundred million, with twenty-five to thirty million of this total assignable to the Mexican and an approximately equal number to the Andean civilizations. Relatively dense populations also apparently existed in the connecting Central American lands.
¹⁰