Plagues and Peoples

In Plagues and Peoples, William H. McNeill argues that patterns of disease have integrally influenced human history from prehistory to the modern day. Until 1976, the year of this book’s publication, the historical study of disease was treated as a footnote of minor importance compared to war, agriculture, and politics. By contrast, McNeill takes a broader view and breaks human history into two categories. The forces of ecology and humanity are equally weighed in McNeill’s telling, and his work on the subject changed the scope and nature of history after him, forcing the study of human history—with its stories of great people and iron wills—to conform to larger fields of study.

McNeill begins 100,000 years ago in sub-Saharan Africa, and speculates that many of the numerous protozoa, fungi, and bacteria found in that part of the world today must have been as similar to millennia-old microparasites as modern day humans were to the first examples of Homo sapiens (which is to say, very similar). In such a tropical climate, microparasites must have thrived, but so too did humanity. A precedent was set; humans and parasites depended on one another for survival and gained nothing from one or the other’s destruction. What is known as illness is the result of imbalance in this system as a result of sudden change.

Such changes were invisible to early humankind and would remain so until very recently in human history, so as humanity became accustomed to describing itself, it left out what it could not see. Disease was a matter of folkways designed around safety and health, and the rest was left to religion and mythology. These balances followed humanity as the Ice Age receded and humankind began to spread out beyond its equatorial confines.

The agricultural revolution spread humanity beyond small bands of hunter-gatherers, and the domestication of animals and increased civilized pools of humanity increased the spread and stock of microparasites shared among humans, while stocks of housing and crops increased the number of wild pests, such as rats and lice, later associated with new forms of disease. Slowly, familiar diseases went from being epidemic (wiping out whole communities at a go) to endemic (falling into the category of diseases affecting limited groups, such as children or the elderly).

The large scale technological and infrastructural change to follow affected the course of disease spread. Writing allowed a more accurate picture of where and when disease spread. The Mongol empire improved the infrastructure of continent-wide Eurasian travel, while Europeans seeking trade routes both within the Mediterranean and then far beyond it, improved the speed and efficiency of travel by sea. These new forms of travel ensured that chains of disease transference became globalized over a long period of time. Likewise, these patterns affected cultural norms and traditions, and early religious texts include several references to disease.

The globalization of disease dealt a massive blow to the advanced and well-developed civilizations of the pre-Columbian Americas, killing vast majorities of people in a short time. At the same time, people on the Eurasian landmass began to grow more resilient to the diseases to which they had long been exposed. With the invention of the microscope and the development of long-standing vaccine practices, humankind made great technical strides in combating disease. As for the future, McNeill warns that “ingenuity, knowledge, and organization alter but cannot cancel humanity’s vulnerability to invasion by parasitic forms of life” (295).

Note on Key Figures section: McNeill’s book resists centering humanity and provides only a few words in passing to the sort of important figures on whom other history books would expend whole chapters. Instead, McNeill argues that the unique nature and movement of various diseases were instrumental in shaping society. Some of the key illnesses are listed in this section.