Read Online Plagues and Peoples by William H. McNeill - Free Book Online Page B

difference for the following year’s plant growth. To be sure, in the case of “dry farming,” soil kept in a bare fallow can store moisture that would otherwise be dispersed into the air by passage of water from the soil through the roots and leafy parts of plants. In regions where deficient moisture limits crop yields, a year’s fallowing can, therefore, increase fertility by letting subsoil moisture accumulate. Elsewhere, however, where moisture is not the critical limit to plant growth, the great advantage of fallowing is that it allows farmers to keep weeds at bay by interrupting their natural life cycle with the plow
    Digging (or flooding) would of course achieve similar results; but in most environments human muscles did not alone suffice to break up enough land in a year to allow a family to subsist on the crop that could be harvested from only half of the cultivated area, while the rest was fallowed. Special soils and ecological conditions did allow some exceptions. The two most significant were (1) North China, where friable and fertile loess soil permitted human populations to subsist on crops of millet without the assistance of animal strength hitched to the plow; and (2) the Americas, where the high calorie yield per acre of maize and potatoes as compared with the Old World crops like wheat, barley, and millet, led to similar results even on soils less easily tilled than the loess of China. 3
    One must admire the skill with which humankind discovered and exploited the possibilities inherent in remodeling natural landscapes in these radical ways, increasing human food supply many times over, even though it meant permanent enslavement to an unending rhythm of work. To be sure, the plow used animal strength to pull the share through thesoil, and the plowman’s life was generally less toilsome than the lot that fell to the rice farmer of East Asia, who used his own muscles for most of the tasks of water and soil engineering required to create and maintain paddy fields. But toil—persistent, unending, and fundamentally at odds with humankind’s propensities as shaped by the hunting experience—was nevertheless the lot of all farming populations. Only so could man the farmer successfully distort natural ecological balances, shorten the food chain, magnify human consumption and multiply human numbers until what had been a relatively rare creature in the balance of nature became the dominant large-bodied species throughout the broad regions of the earth susceptible to agriculture.
    The struggle with weeds (including what we may call weed animals, like weevils, rats, and mice) was conducted with the help of tools, intelligence, and experiment; and though unending, it led to a series of victories for humanity. There was, however, another side to the agriculture distortion of natural ecological balances. Shortening the food chain and multiplying a restricted number of domesticated species of plants and animals also created dense concentrations of potential food for parasites. Since most successful parasites were too small to be seen, for many centuries human intelligence could not cope very effectively with their ravages.
    Prior to the dawn of modern science and the invention of the microscope, therefore, our ancestors’ victories over weeds and rival large-bodied predators, remarkable as they were, met a counterforce in the extended opportunities small-bodied parasitic predators found in the altered landscapes successful farmers created. Hyperinfestation by a single or a very few species is, indeed, a normal response to any abrupt and far-reaching alteration of natural balances in the web of life. Weed species live by exploiting the gaps disasters create in normal ecological systems. Weeds remain rare and inconspicuous amid undisturbed natural vegetation, but are able rapidly to occupy any niche created by destruction of local climax cover. Since few species are equipped to exploit such opportunitiesefficiently,