Plagues and Peoples (22 page)

Precisely the same considerations apply also to the British Isles. The surprisingly low level of British population in medieval times as compared to that of France, Italy, or Germany, may owe far more to the vulnerability of an islanded population to epidemic attrition than to any other factors. Without a lifetime of research, however, it is unfortunately not possible to compare the epidemic experience of Britain with that of the continent of Europe, since there is no continental equivalent to Charles Creighton’s classic,
A History of Epidemics in Britain
. Yet the very fact that Creighton could assemble so much data for the British Isles may itself reflect the fact that epidemics mattered more in Great Britain than on the main-
land of Europe, where the shift to endemicity presumably occurred earlier because populations were larger and had more nearly uninterrupted contact with urban (initially, Mediterranean) sources of infection.

Moreover, in both Great Britain and Japan a critical threshold was eventually crossed when earlier vulnerability to epidemic disaster ceased to manifest itself. In Japan the transition took place in the thirteenth century; in Britain the catastrophic intervention of the Black Death in the mid-fourteenth century delayed matters, so that sustained population growth only set in after 1430. But once they had crossed the critical epidemiological threshold, Japanese and British populations both exhibited more dynamic growth than occurred on the adjacent mainlands. The effect in Japan was dramatic. A plausible estimate of Japanese total population runs as follows
⁸⁸
:

Period	Millions
ca. 823	3.69
859–922	3.76
990–1080	4.41
1185–1333	9.75

As for Great Britain, comparable estimates are only available for England
⁸⁹
:

Period	Millions
1086	1.1
1348	3.7
13 77	2.2
1430	2.1
1603	3.8
1690	4.1

Here the downturn resulting from the Black Death is dramatically apparent; and a doubling of population, such as probably occurred in Japan in the 250 years from 1080 to 1333, had its analogue in England only between 1430 and 1690, when population also almost doubled.

The laggard adjustment to infections that thus becomes evident in Britain and Japan can be clearly related to the political and military history of the two islanded peoples. England’s record of moving into and subduing the Celtic fringe within the British Isles is well known; the further effort to conquer France, beginning in 1337, illustrates an even more ambitious scheme for utilizing the strength inherent in a growing population. Once the Black Death struck, of course, the force went out of both movements. English expansion was resumed only under Elizabeth in the second half of the sixteenth century. In Japan’s case the pace of expansion within the archipelago itself (at the expense of the Ainu) and overseas (at the expense of Koreans and Chinese) also assumed noticeably greater speed and force from the thirteenth century onward. A big factor in this phenomenon must surely have been the achievement of a new disease balance within Japanese society, as once damaging epidemics coming from outside transformed themselves into less costly endemic infections.

Unfortunately, nothing in available scholarly writing allows any similar reconstruction of the disease history of the rest of the world. Very possibly, most of the new diseases to which European and Far Eastern populations had to accustom themselves in the centuries between
A.D
. 1 and
A.D
. 1200 had evolved previously in India and the Middle East. Plague, at any rate, seems pretty surely to have diffused east and west via the shipping lanes of the Indian Ocean; and the rash and fever afflictions that visited both the Roman and the Chinese worlds arrived by land routes, i.e., proximately, if not necessarily ultimately, from Middle Eastern lands.

Plague, when it came to Rome, came also to Mesopotamia and Iran, and may have been quite as devastating in those regions as it was in the Mediterranean.
⁹⁰
Since maintenance of canals required massive annual effort, any decay of population in Mesopotamia was sensitively registered by the abandonment of canals formerly in use. Modern surveys discover such a retreat in generations just before the Arab conquest in 651. Decay continued after the conquest as well.
⁹¹
There is no
reason to suppose that the Moslem newcomers wreaked any very significant damage to the irrigation system, since the Arabs were already familiar with irrigation and had no interest in destroying potential taxpayers. It therefore seems probable that something else upset the population balance of Mesopotamia. Although salting and other technical difficulties may have already made the irrigation system precarious, recurrent exposure to plague offers a plausible explanation of the precipitous decay of Mesopotamian population that accompanied and followed the Arab conquests of the seventh century
A.D
.

As for India, the existence of temples for worship of a deity of smallpox shows that the disease (or something closely akin thereto) was of considerable significance in Hindu India from time immemorial—however long that may be historically. Unfortunately, absence of records permits no account whatever of Indian encounters with infectious disease before 1200.

Because smallpox and measles are especially spectacular when they attack virgin populations, and because plague remained spectacular in its incidence always, these diseases almost monopolize literary references in those cases when it is possible to surmise what infection caused some sudden and large-scale die-off. But the same changes in human patterns of communication that propagated these infections in new regions obviously allowed other diseases also to circulate beyond earlier limits. This seems to have been the case with the disease modern doctors call leprosy, for a special study of more than 18,000 skeletons showed no signs of the disease until the sixth century
A.D
., when it appeared in Egypt, France, and Britain.
⁹²
On the other hand, skin ailments that fell under the Old Testament ban on leprosy must have been much older. The establishment of special houses for lepers is attested in Europe as early as the fourth century
A.D
., but this should not be interpreted as evidence of the arrival of a new disease. Rather, it was probably the result of the Roman government becoming Christian and taking seriously biblical injunctions about how to treat persons with disfiguring skin diseases.
⁹³

Other diseases must also have found new geographic range in the early Christian centuries. Some of them, tuberculosis, for example, or diphtheria and influenza, together with various forms of dysentery, may have exerted demographic effects comparable to the effects of smallpox, measles, and plague. Moreover, formerly formidable local diseases may have disappeared when forced to compete with some invading infection; at least, as we shall see in the next chapter, there is some reason to think that this happened in later times when new and drastic epidemics afflicted Europeans.

Uniformity of infectious patterns was never attained; but despite innumerable local variations, defined by climatic and other ecological factors, it seems reasonable to conclude that within the circle of Old World civilizations, a far more nearly uniform disease pool was created as a by-product of the opening of regular trade contacts in the first century
A.D
. By the tenth century, the biological adjustments provoked by this reshuffle of infectious patterns had had time to work themselves out both in Europe and in China, with the result that population began again to rise in each of these civilized areas. Correspondingly, the relative weight and mass of China and of Europe vis-à-vis the Middle East and India began to grow. Subsequent world history could in fact be written around this fact.

In addition, we may reasonably believe that a fringe of peoples all across Asia, and extending into both eastern and western Africa, entered at least marginally into the disease circulation centering in the older civilized lands. Moslem and Christian traders and missionaries penetrated far into the Eurasian steppe and northern forest lands; other pioneers of civilization infiltrated Africa. Everywhere they must have carried with them the possibility of exposure to civilized diseases, at least on a sporadic, occasional, once-a-generation or once-a-century basis.

Occasional heavy die-offs of some hitherto isolated population must often have occurred. Among the survivors, however, adjustment to the new epidemiological patterns of the
Old World seems to have proceeded among the steppe peoples about as rapidly as it did in northwestern Europe. The reason for saying this is that Turks and other nomads, when they penetrated civilized landscapes, whether in Asia or in Europe, do not seem to have suffered any very sharp disease consequences. If they had been completely inexperienced with civilized diseases in their steppe homelands, these nomad invaders would have died off very quickly.

The conquests and ethnic encroachments which Turks and Mongols achieved before, and more spectacularly after,
A.D
. 1000 simply could not have occurred had these peoples not achieved and maintained a level of immunity to civilized diseases almost equivalent to that prevailing in the major civilized centers themselves. Everything known of the trade patterns and political structures of the steppe make this seem likely, indeed all but certain. Frequent movement across long distances, and occasional assembly into large gatherings for raids or (with the Mongols) for a great annual hunt, provided ample opportunity for infectious diseases to be exchanged and propagated among the nomads, and even, as Chinese records attest, to be sometimes communicated to less mobile civilized populations.

Trade and Islamic missionaries penetrated much of Africa in exactly the same way as other Moslem traders and missionaries roamed the Eurasian steppe; and presumably with almost the same epidemiological effect, although in many African landscapes diseases peculiar to that continent presented barriers to alien intrusion more formidable than anything present in other parts of the earth. Hence civilized encroachment was restricted and, mayhap, African exposure to civilized diseases may have been less thoroughgoing than was true in the Asian steppes. On the other hand, when African slaves began to come to the New World after 1500, they suffered no spectacular die-off from contact with European diseases, which is sufficient demonstration that in their African habitat some exposure to the standard childhood diseases of civilization must have occurred, if not before, then soon after 1200.

In the New World, on the contrary, the Eurasian epidemiological experience of the first Christian millennium had no echoes whatever. As population thickened and civilized centers arose in Mexico and Peru, comparatively vast human communities came into being that were highly vulnerable to Old World infections. Civilized Amerindians after 1200 were therefore like Mediterranean and Far Eastern peoples at the beginning of the Christian era: populations dense enough for epidemic decimation. But before exploring the fateful implications of this circumstance, we must first consider a second great Eurasian epidemiological upheaval, centering on the Black Death of the fourteenth century.

IV

The Impact of the Mongol Empire on Shifting Disease Balances, 1200–1500

I

f the disease history of the Old World as reconstructed in
Chapter III
is correct, at least in its main lines, one may conclude that epidemiological adjustments arising from the establishment of regular communication across the spaces separating one civilized community of Eurasia from another had worked themselves out by about
A.D
. 900 into a relatively stable pattern. That is to say, by that time human populations had adjusted to the confluence of the various infectious diseases that in earlier times had developed differently in different parts of Eurasia and Africa. In all probability, no considerable population within the ecumene remained altogether inexperienced with any of the major person-to-person epidemic infections, although in many places such diseases appeared only at intervals when an accumulation of susceptible age classes provided the tinder needed to sustain an epidemic conflagration.

Two systematic instabilities remained. One was the persistent and cumulatively massive growth of human population in the Far East and Far West, resulting from the way in which
the Chinese and Europeans had broken through older epidemiological and technological barriers shortly before
A.D
. 900. Eventually this development affected the macro-balances of the Old World in emphatic fashion, making first China and then western Europe critically influential in military, economic, and cultural matters. The other source of systematic instability within the Eurasian world balance, as defined between 900 and 1200, was the possibility of further altering communications patterns, both by sea and land.

The first such change that affected both macro- and micro-parasitic patterns in far-reaching ways was the intensification of overland caravan movement across Asia that reached its climax under the Mongol empires founded by Genghis Khan (1162–1227). At the height of their power (1279–1350), the Mongol empires embraced all of China and nearly all of Russia (the distant Novgorod alone remained independent), as well as central Asia, Iran, and Iraq. A communications network comprising post messengers capable of traveling one hundred miles a day for weeks on end, and slower commercial caravans and armies, marching to and fro across vast distances, knitted these empires together until the 1350s, when rebellion flared within China, leading by 1368 to the complete expulsion of the Mongols from their richest conquest.