Plagues and Peoples (11 page)

Person to person, “civilized” types of infectious disease could not have established themselves much before 3000
B.C
. When they did get going, however, different infections established themselves among different civilized communities in Eurasia. Proof of this fact is that when communications between previously isolated civilized communities became regular and organized, just before and after the Christian era, devastating infections soon spread from one civilization to another, with consequences for human life analogous to, though less drastic than, what happened to rabbits in Australia after 1950.

Closer consideration of these events will be reserved for the next chapter. Here it seems only needful to reflect briefly about the general historical consequences of the establishment of these distinctively civilized sorts of diseases in a few centers of unusually dense human population between 3000 and 500
B.C
.

First and most obvious: patterns of human reproduction had to adjust to the systematic loss of population that resulted from exposure to diseases that flourished under civilized conditions. Until very recently cities were unable to maintain their numbers without a substantial inflow of migrants from surrounding countrysides. Urban health hazards were simply too great, for, in addition to infectious person-to-person diseases transmitted as childhood diseases usually are—by breathing in droplets of infectious matter sneezed or coughed into the atmosphere—ancient cities suffered from an intensified circulation of diseases transmitted through contaminated water supplies, plus a full array of insect-borne infections. Any breakdown of transportation bringing food from afar threatened famine, and local crop failures were often difficult to compensate for. In view of all this it is not surprising that cities could not maintain themselves demographically, but had to depend on migrants from the countryside to replenish the losses arising from famine, epidemic, and endemic diseases.

A civilized pattern of life therefore required rural cultivators not only to produce more food than they themselves consumed in order to feed urban dwellers, but also to produce a surplus of children whose migration into town was needed to sustain urban numbers. Rural reproductive surpluses had also to be capable of bearing losses resulting from macroparasitism, i.e., from war and raiding, and from the famine such activities nearly always provoked. Only occasionally and for limited periods of time was anything like a stable balance attained between rural birth rates and occupational niches available in urban contexts for the surplus from the countryside. Open and accessible frontiers—so important for European history in the past four centuries—were also unusual, though when land was available, surplus rural population could and did migrate to the frontier and thereby enlarge the agricultural base of the society instead of trying the risky (though to a few, spectacularly rewarding) path of migration into town.

Until after 1650, when population statistics begin to assume a degree of reliability, it seems impossible even to guess at the magnitudes involved in this pattern of population flow. Nevertheless, such patterns clearly asserted themselves from the time cities first formed. The striking way, for example, in which Sumerian-speakers gave way to Semitic-speakers in ancient Mesopotamia during the third millennium
B.C
.
³⁹
is probably a direct consequence of this kind of population movement. Speakers of Semitic tongues presumably migrated into Sumerian cities in such numbers that they swamped speakers of the older language. Sumerian lingered on as a language of learning and priestcraft, but for everyday purposes, the Semitic Akkadian took over. This linguistic shift might have resulted from a spurt of urban growth, or more likely from an unusually heavy die-off of established urban populations because of disease, war or famine, although which of these factors or combination of factors may have been at work in ancient Sumer is not known.

A nineteenth-century parallel may be useful. From the 1830s and especially after 1850, rapid urban growth together
with the ravages of a new disease, cholera, disrupted cultural patterns of long standing in the Hapsburg monarchy.
⁴⁰
Peasant migrants into the towns of Bohemia and Hungary had long been accustomed to learn German, and in a few generations their descendants became German in sentiment as well as in language. This process began to falter in the nineteenth century. When the number of Slav- and Magyar-speaking migrants living in the cities of the monarchy passed a certain point, newcomers no longer had to learn German for everyday life. Presently nationalist ideals took root and made a German identity seem unpatriotic. The result was that Prague became a Czech- and Budapest a Magyar-speaking city within half a century.

Early civilizations that were linguistically more uniform obviously did not register the process of migration into town by linguistic change as ancient Mesopotamia and the nineteenth-century Hapsburg monarchy did. Nonetheless, the reality of urban population wastage in very ancient as well as in more recent times cannot be doubted. The mere existence of cities and the intensified patterns of disease circulation they created must have led to this result, with only as much delay as was needed for disease organisms to discover and work themselves into the enriched environment urbanized humanity presented for their nutriment.

How the flow of surplus population from the countryside was provoked and sustained is not at all clear. To be sure, the country was often healthier, since various forms of infection rife in cities were less likely to reach rural dwellers. On the other hand, when an epidemic did penetrate the countryside it could have more drastic consequences than were likely among an already diseased and therefore partially immune urban population. Moreover, many peasantries were chronically undernourished and therefore especially vulnerable to any infection that happened along. Clearly, peasantries subjected to civilized control did not automatically find it easy to raise more children than were needed to keep the family operation
going, any more than they found it easy to produce more food than they themselves required for survival.

Yet universally they accomplished both of these tasks. Civilizations could not have persisted without a flow of migrants as well as a flow of food from countryside to city. It is, therefore, altogether probable that moral codes encouraging a high rural birth rate were a necessary underpinning for civilized patterns of society. At any rate, the various means by which hunting and gathering communities regulated their numbers have not prevailed among civilized peasantries. Instead, in most if not all peasant societies, early marriage and a long string of children has been regarded as a sign of moral excellence and divine favor, as well as the best of all possible assurances against a helpless old age, since if one child should die another can still take on the responsibility for looking after the old folks when they are no longer able to support themselves. These attitudes were also connected with recognition of individual and familial property rights to land. Such rights were often, in turn, defined or reinforced by governmental policy with respect to rent and taxes.

Exactly how cultural, social, and biological factors acted and reacted upon each other, however, is impossible to tell. All we can be sure of is that successful civilizations all managed to assure a flow of persons as well as of goods from the countryside into the cities, and they did so through combining the sanctions of religion, law and custom.

As will be readily appreciated in our age of explosive population growth, the civilized reproductive norm ran the risk of provoking acute rural overpopulation. Any prolonged slackening of career opportunities for the peasant surplus—in cities, armies, or by emigration to some frontier region—soon had the effect of ponding excess population back in villages. To forestall rural overpopulation, alternative careers had to involve high death rates, yet without deterring large numbers of men and women from accepting the risks involved, whether they did so voluntarily or involuntarily, knowingly or in ignorance, of the probable upshot of leaving home.

To keep a stable demographic balance under such circumstances was and is exceedingly difficult. Urban and military die-off must match rural growth rates, and the whole community must simultaneously succeed in defending itself against “outside” invasion so massive as to upset its internal demographic pattern.

A genuinely stable macroparasitic pattern conforming to these specifications has rarely existed for long in any part of the world. Instead, civilized history has characteristically exhibited sharp fluctuations up and down, as periods of peace and prosperity induced population growth in excess of macroparasitic powers of absorption (i.e., destruction); whereupon an increase in death rates asserted itself through the breakdown of public order. Peasant revolt, civil war, foreign raid and rapine, together with accompanying intensification of famine and disease, could always be counted on to reduce populations catastrophically whenever less drastic regulators of peasant numbers failed to maintain a satisfactory balance.

Characteristically, heightened death rates would cut back peasant numbers far below previous levels before successful political consolidation would again allow rural population growth to assert itself. Obviously, “outside” invasions—whether by disease organisms or by armed men—were capable of interrupting such cycles; so could unusual climatic conditions that resulted in heavy crop losses. Indeed, in most of the civilized world such “outside” factors were so powerful and so frequent as to mask any close correlation between the oscillation of peasant numbers and the level of public peace. Only in China, where external political-military forces were weaker because geographic barriers insulated the civilized human mass from important foreign pressures most of the time, did this cycle manifest itself unmistakably; though even there, extraneous factors were never entirely absent and sometimes held back population recovery for centuries at a time.

Civilized societies had another way of consuming surplus population from the countryside. By mounting attacks on
neighboring regions, kings and armies were sometimes able to expand the territories under their control and open frontier lands for their subjects to settle and exploit. Such enterprises, indeed, offered an all but infallible solution to any danger of overpopulation at home, since a notable increase in the number of deaths could always be expected from wars of conquest, whether they were successful or not.

Trade, too, sometimes allowed the support of otherwise surplus population. Until recent centuries, however, the cost of transportation overland was so high that significant numbers of people could prosper through trade only by locating themselves near the sea or along navigable rivers. Nevertheless, from the earliest days of civilization ships could and did bring food and other useful commodities from afar to a number of ports. By exchanging manufactures and other goods for food and raw materials, civilized merchants and seamen could engage in mutually advantageous trade with foreigners. But it was as difficult to maintain trade balances in a steady state as it was to maintain a stable demographic balance within a single political community. Hence, sharply alternating expansion and contraction was the rule in trade as well as in politics and war.

With such multiple instabilities built in, it seems clear that civilized society has not yet attained anything like a well-adjusted ecological balance on the macroparasitic level. Like a disease invading an inexperienced host population, the incidence of civilized forms of macroparasitism have fluctuated sharply through recorded history—sometimes killing off excessive numbers of the peasants and other workers who sustained the system by their labor, and at other times failing to hold the number of mouths at a figure to match available food.

Despite innumerable local setbacks, however, the areas subject to civilized patterns of organization did tend to increase across the centuries. Yet the number of discrete civilizations always remained modest, though whether one counts a total of half a dozen or two dozen depends on the criteria used to
distinguish one style of civilized life from another. Such small numbers reflect the fact that civilizations do not characteristically expand by stimulating the elaboration of pre-existing local institutions, ideas, and skills to new heights of sophistication. Instead, civilizations regularly export key cultural elements from an already elaborated center onto new ground. Often, perhaps always, it was easier to borrow and imitate than to create anew. There was, however, another factor in the situation that goes far to explain the comparative ease with which civilized societies expanded into new territories, one that was a result not of conscious policies or of macroparasitic patterns, but of the dynamics of microparasitism. A moment’s reflection will show what these were.

When civilized societies learned to live with the “childhood diseases” that can only persist among large human populations, they acquired a very potent biological weapon. It came into play whenever new contacts with previously isolated, smaller human groups occurred. Civilized diseases when let loose among a population that lacked any prior exposure to the germ in question quickly assumed drastic proportions, killing off old and young alike instead of remaining a perhaps serious, but still tolerable, disease affecting small children.
⁴¹

The disruptive effect of such an epidemic is likely to be greater than the mere loss of life, severe as that may be. Often survivors are demoralized, and lose all faith in inherited custom and belief which had not prepared them for such a disaster. Sometimes new infections actually manifest their greatest virulence among young adults, owing, some doctors believe, to excessive vigor of this age-group’s antibody reactions to the invading disease organism.
⁴²
Population losses within the twenty-to-forty age bracket are obviously far more damaging to society at large than comparably numerous destruction of either the very young or the very old. Indeed, any community that loses a substantial percentage of its young adults in a single epidemic finds it hard to maintain itself materially and spiritually. When an initial exposure to one civilized infection is swiftly followed by similarly destructive exposure to others,
the structural cohesion of the community is almost certain to collapse. In the early millennia of civilized history, the result was sporadically to create a fringe of half-empty land on the margins of civilized societies. Simple folk brought into contact with urban populations always risked demoralizing and destructive disease encounters. Survivors were often in no position to offer serious resistance to thoroughgoing incorporation into the civilized body politic.