What we can—and can’t—learn from the plague

The illness changed everything. It originated in Asia, in the cohabitation of people with animals. Fortified by their passage through the Fertile Crescent of the Middle East, where peasants shared muddy yards with cows, horses, sheep, goats, pigs, chickens, dogs and cats, the microbes borne by fleas embedded in the fur of black rats hopped to other animals, then to people. Those infected suffered from chills and breathing difficulties; they were wracked by diarrhea and vomiting; they bled from the mouth and the rectum. Death came within days, or even hours. By 1347 the plague had reached Europe. Over the next five years, as much as half of the continent’s population died. The survivors inherited a strange, empty world, where cities were quiet and peasants expanded their holdings by taking over plots of land that had been cultivated by those now deceased. The structures of feudal land tenancy began to break down. Food became cheaper, yet, over time, a shortage of agricultural labourers hampered Europe’s food production.

The plague did not go away. It came back in waves. The poet Geoffrey Chaucer, who would have heard of the Black Death as a child in England in the 134s, must have witnessed the outbreaks of the 136s as a young man. In “The Pardoner’s Tale,” Chaucer wrote: “An unseen thief, called Death, came stalking by/ Who hereabouts makes all the people die.” Societies went into lockdown again and again. In early seventeenth-century England the theatrical career of William Shakespeare was interrupted at crucial points when social distancing closed theatres for months or years; forty years later Pedro Calderón de la Barca, one of the greatest playwrights of the era, suffered a similar fate in Spain.

The changes brought on by the disease were moral, political, even biological. One of the inspirations for “The Pardoner’s Tale” was Giovanni Boccaccio’s The Decameron, completed in about 1353. In this massive, monstrously entertaining book, ten well-born people aged between eighteen and twenty-eight flee Florence, Italy, where the plague has killed nearly one hundred thousand people, to go into self-isolation in farmhouses in the hills. Boccaccio observes that though all of the young women in the group are devout and dressed in mourning garb, he will not call them by their real names because, “I do not want any of them to feel shame in the future because of the ensuing stories, which they either listened to or told themselves.” The plague, Boccaccio remarks, relaxed the rules of morality. In the face of death, pleasure took precedence over propriety. For ten days Boccaccio’s pious young people tell each other the filthiest, most lascivious stories they can think up. During a hiatus in this verbal orgy, one of their leaders remarks that, “since everything has been turned upside down nowadays… the laws, divine as well as human, have fallen silent.”

The memory of the plague was passed down to later centuries. In Sigrid Undset’s epic novel of life in fourteenth-century Norway, Kristin Lavransdatter (1927), which some critics regard as the greatest historical novel of the twentieth century, most of the central characters die of the plague. The protagonist, Kristin, by this point in the story a woman in late middle age, leaves her farm to live in a convent where she, also, contracts the illness and dies. While most of her family perishes, one of Kristin’s sons is immune to the disease. The recognition that he is a genetic fluke alters his morality: “he had plunged into wild living, as had many young men in this desperate pass… Even honourable burghers’ wives and young maids of the best kindreds ran from their homes in this evil time; in company with the women of the bordels they caroused in the inns and taverns.”

Those who were genetically less disposed to die from the plague became the stock from which Europe’s population was replenished. One hundred and forty years later, in the late fifteenth century, the descendants of the plague’s survivors invaded the Americas. The microbial shock between the post-plague, ethnically mixed colonizers and the much more ethnically uniform Indigenous people, who had no history of cohabiting with livestock or being genetically groomed for survival against animal-borne diseases, caused Indigenous populations in the Americas to plummet by ninety percent even before oppressive colonial systems were fully implemented. In Europe, meanwhile, the post-plague shortage of agricultural labourers continued to inhibit food production. The crisis was particularly acute in Portugal, one of the continent’s poorest countries. By opening up trading relations with societies from Sierra Leone to the southern Congo, initially in fabric, salt and gold, but later in the tainted commodity of human beings, between 1441 and 155 the Portuguese brought more than 15, Africans into their country as slaves. Arriving in a nation whose population was barely one million people, the Africans changed Portugal’s ethnic composition. Portugal’s importation of Africans to work in its fields initiated the Atlantic slave trade, which would continue for four centuries and create the modern African-descended populations of the Americas. Population depletion in rural Europe was the impetus behind the slave trade, which, in turn, depleted the populations of large areas of the African interior. Portugal went on to colonize Cabo Verde, Guinea, Angola and Mozambique. One of the ironies of later Portuguese colonialism in Africa was that, since nearly fifteen percent of the population of fifteenth-century Portugal was African—a population that did not remain a discrete ethnic group, but rather became indistinguishable from other Portuguese as the result of centuries of miscegenation—most of the white colonial administrators sent out from Lisbon in the nineteenth century to run the colonies had remote African ancestry.No one foresaw these changes. A woman dying in a convent in Norway, a peasant afflicted by plague in the south of France, a family of children watching each other cough and bleed in rural Portugal or a young person in a tavern venting their bewilderment at having been spared, could not know that their suffering would weaken the feudal system, facilitate the colonization of the Americas or become a catalyst for the Atlantic slave trade. We know little more. Our laboratories can test individuals and project infection patterns. They cannot predict what will be obvious to those who look back on this time in future centuries: how illness changed history.