Lecture #3: Migration, Disease, and Death

Suggested Readings:

William H. McNeill, Plagues and Peoples (1976)

Alfred W. Crosby, Jr., The Columbian Exchange (1972)

Samuel K. Cohn, The Black Death Transformed: Disease and Culture in Early Renaissance Europe (2003)

Kenneth F. Kiple, The Cambridge World History of Human Disease (1993)

David S. Jones, Rationalizing Epidemics: Meanings and Uses of American Indian Mortality since 1600 (2004)


I. Prelude: The Black Death

migration of organisms between ecosystems is a central theme in environmental history world-wide

disease fundamental to environmental history: the bodies of humanings serve as the environments in which disease organisms reproduce and thrive

movement of epidemic diseases not limited to trans-oceanic Old World/New World migration

among the most famous of all epidemics in world history: Black Death, beginning in Europe in 1346: massive consequences whose effects lasted for decades, even centuries

plague originated in the foothills of Himalayas, Burma; Mongol caravans as vehicles for transporting it westward.

old story: plague endemic to rats and other rodents, transmitted by fleas living in rodent community

movement of plague west from Burma to China to Europe infected human and rat populations

differential effects: like a childhood disease for rats, often with limited mortality; but in humans, 30%-90% mortality

recent historiographical controversy: Samuel Cohn and others have argued that rats and fleas could not have caused the Black Death: anthrax?

the words and understandings that inform our own thinking today about this disease are only partly relevant to our understanding of its history in the 14th century (and how that history was understood by people of the time)

four years after plague started in Europe in 1346, 1/3 of the population of that continent was dead: 25 million people


human migrations are always accompanied by other creatures, some of which are lethal for their human hosts;

we share many of of our most important illnesses with other animals (epidemics in humans are called epizootics in animals);

disease can be endemic to some areas, but absent in others...and therefore epidemic when it occurs:

changing transport technologies turn trade corridors into disease vectors (war can play a role as well);

late Middle Ages were a time of increasing contact between Europeans and rest of world:

spread of diseases to parts of the world where they had previously been absent was fundamentally linked to this process, both imported into Europe and exported out of it

II. Virgin Soil Epidemics

it's not generally a successful evolutionary strategy for disease organisms to wipe out their host populations, since they put their own ecosystem at risk if they do so (cf rats/humans relative to the plague)

the antibodies of our immune systems serve as defensive tools for host populations: diseases trigger us to generate new antibodies as they reproduce themselves inside us, leading to a perennial race in which diseases seek to reproduce and transmit themselves to new hosts before the old host can generate effective antibody defenses

disease immunities are often more historical than genetic: a population's history of exposure to a given disease allows mothers to transmit antibodies to offspring in utero and through breast milk

herd immunity: collective pool of antibodies protects population as a whole from disastrous epidemics

crucial: native populations of the Americas lacked any historical immunological experience of many Old World diseases: measles, smallpox, chickenpox, mumps, malaria, yellow fever, etc., were all absent from the Western Hemisphere at the time Columbus made his voyage in 1492

as a result, those populations were comparatively healthy, but also vulnerable and very much at risk when exposed to disease organisms migrating from Eurasia and Africa

why did they lack immunity to these disease organisms? several reasons:

  • migration via cold northern environments of the Arctic, inhospitable to illnesses;
  • migration in populations too small to act as self-sustaining hosts to disease organisms;
  • brought no domesticated animals to act as additional host pool for diseases;
  • migrated prior to periods when historic illnesses of Eurasia developed.

as a result, migrating Indians shed Eurasian illnesses as they migrated (if they had ever been exposed to them), and thereby lost their historical immunity to them

reintroduction of disease organisms into such populations produces "virgin soil epidemic"

such epidemics proved to be especially devastating to mature adults in their prime reproductive years, as well as to infants

it's not that individuals are more or less susceptible to infection, but rather that the population as a whole has statistical vulnerability

classic virgin soil epidemics have occurred on relatively small islands, or in isolated populations: smallpox epidemic in Iceland in 1717 a classic example

note also that emerging immunity to one invading infection provides no protection to other such infections, with the result that repeated waves of epidemics became part of the biological population of native populations in the Americas: a classic example in the twentieth century occurred during the construction of the Alcan Highway during World War II in 1942-3

III. We Were Born to Die (Mayan lament)

earliest trans-Atlantic disease migrations were non-virulent endemic illnesses--diarrheas, dysentaries, respiratory illnesses, sexually transmitted diseases--capable of surviving the voyage on board ship without burning themselves out in their European and African host populations

it was more difficult for more virulent organisms to make their way across the ocean, since they had to keep finding new hosts throughout journey in order to reach the other side of the Atlantic

1518: smallpox appeared Santo Domingo (modern-day Dominican Republic), and one-third to one-half of the natives died in few months

1521: smallpox aided Cortes in his conquest of Tenochtitlan, capital of the Aztec empire

repeated epidemics, with many different diseases, brought centuries-long population decline for native peoples throughout the Americas

at least 35 separate recorded episodes of smallpox alone between 1520-1898; cf Mandan epidemic, 1837

IV. Counting Up the Victims

the myriad demographic effects of these epidemics have only come to be understood by scholars over the past few decades

early population estimates followed James Mooney's Aboriginal Population of America North of Mexico (1928), which estimated that the total population of Indians in all of North America at the time Columbus made his voyage was just 1.1 million

W. W. Borah and S. Cooke begin gathering data in the 1930s and 1940s to try to estimate the scale of mortality especially in Mexico & California, and concluded that death rates were far higher than originally imagined

1966: Henry Dobyns assumed a mortality rate of 90% and calculated pre-Columbian North American Indian population at 10-12 million, with the population of the entire hemisphere amounting to 90-110 million

Dobyns' arguments generated much controversy and his estimates were likely too high, but they scholars today all agree that native populations in the Americas suffered terrifyingly high mortalities in the wake of being exposed to Eurasian epidemics

key conclusion: European migration produced decline in North American Indian populations from 10 to 1 million

dramatic social, economic, political, cultural consequences, which we'll explore during the next couple weeks

V. The Continuing Migration of Death

the migration of disease organisms reproduced Old World disease environments not just for native populations, but for Europeans as well

African diseases in South Carolina favored African slaves in rice-growing areas (malaria, sickle cell)

Recent experiences with HIV-AIDS, West Nile virus, Ebola, suggest that this process of disease migration continues to this day