Pathogenesis: A History of the World in Eight Plagues

by Jonathan Kennedy

The Mississippian culture, the most advanced society in North America, which had thrived for more than 500 years, had simply vanished. By far the most plausible explanation is that the population was obliterated by successive waves of infectious diseases brought by Europeans.

If modern-day Americans want to be historically accurate, then their gratitude at Thanksgiving should be directed to the Old World pathogens that made the settlement of Plymouth Colony possible.

The epidemic that devastated the indigenous population in the years before 1620 benefited the colonists in another important way: by unsettling the power balance between rival Native American communities in the region. The Wampanoag—who had been particularly badly hit by the epidemic—were willing to ally with the English in order to strengthen their position against Native American communities who hadn’t been as affected.

Here European goods were exchanged for gold, as well as spices and enslaved humans. The Portuguese weren’t even equals in these endeavors. In most cases, the hosts dictated the terms of European fortune seekers’ stays and anyone who violated the rules faced harsh punishment, including death.

But the experiences of Portuguese explorers contrasted starkly with those of their Spanish contemporaries. While the Mexica and Inca Empires collapsed, West African polities remained resolute. The Portuguese only ever made minor inroads in the region. They never found the mines where Musa’s gold was dug up, nor did they control territory beyond a few isolated feitorias on the coast. Infectious diseases are responsible for the very different outcomes. The colonization of the Americas was only possible because Old World pathogens came to the conquistadors’ aid. The Portuguese had no such luck.

Many people in the African interior lived in isolated communities—they hadn’t been exposed to Old World Pathogens and therefore hadn’t developed resistance.[69] Diseases like smallpox, measles and flu might have posed a danger to this latter group, if only Europeans were able to travel throughout the continent. But mosquito-borne diseases made that all but impossible.

The fact that European attempts to settle in the Americas foundered without the help of infectious diseases suggests that the Portuguese would have struggled to colonize West Africa even if malaria and yellow fever hadn’t intervened to help the indigenous population. But these mosquito-borne diseases created a defensive force field that made military conquest all but impossible.

In the late eighteenth and early nineteenth centuries, when Britain was on its way to becoming the dominant colonial force in the world, malaria and yellow fever—the flaming sword of deadly fevers—still made tropical Africa all but unconquerable. The American historian Philip Curtin estimates that around this time between 30 and 70 percent of Europeans died in their first year on the West African coast; little wonder that the region was known to the British as “the white man’s grave.”

The “rivers of gold” that appeared on medieval maps were in reality “rivers of death.”

Curtin’s data suggests that the average European would have survived for just four months in Mali—an annual mortality of 300 percent!

The threat posed by infectious diseases made it impossible for Europeans to colonize most of sub-Saharan Africa. In 1870, only one-tenth of the African land mass was under European control. Compare this to the Americas, where the conquest of the Mexica and Inca had occurred three and a half centuries before, and the whole continent either was or had been under European occupation.

Innovations in transport and weaponry only abetted the Scramble for Africa in conjunction with improvements in the prevention and treatment of malaria. Quinine was crucial in this respect.

The continued threat posed by infectious diseases in tropical Africa had an enormous impact on the specific form that colonialism took. The region attracted ambitious and unscrupulous Europeans motivated by making as much money in as little time and with as small a capital expenditure as possible—and then cutting and running before they were struck down by disease. They weren’t colonial settlers. So, unlike in New England, they didn’t bring their families with them, settle down and build institutions in the image of their home country. Rather, the Europeans who colonized Africa in the last decades of the nineteenth century created “extractive institutions” that used violence and the threat of violence to coerce the population into mining natural resources and transporting them to the coast, where they were shipped to Europe. The ultimate aim of this brutal endeavor was not to build a new and better society, but to enrich a small group of Europeans by draining wealth from the region.

The ten poorest countries in the world are all former colonies in sub-Saharan Africa. It is not unreasonable to conclude that these societies would have been better off if Europeans had never discovered a moderately effective treatment for malaria and the region had remained a white man’s grave.

The median household wealth of African Americans is $17,600 compared to $171,000 for whites,[2] and they are almost six times more likely to be incarcerated.

But New World slavery and its legacy are not exclusively a North American problem. Only about 3 percent of the 12.5 million humans trafficked across the Atlantic ended up in what would become the United States.

The founder of economics, Adam Smith, agreed that New World slavery was morally repugnant, but he also pointed out that it was economically inefficient. In The Wealth of Nations Smith argued that “the work done by free men comes cheaper in the end than the work performed by slaves.” This is because enslaved workers who had no prospect of being freed could only be encouraged to be productive through violence and threats. At the same time, there were enormous incentives for slaves to try to sabotage their workplaces, attack their supervisors and escape from a living hell. According to Smith, the cost of violent supervision required to keep an enslaved labor force in line made it prohibitively expensive.

the emergence of American slavery and the ideology of racism used to justify it had a great deal to do with infectious diseases—and who could, or could not, survive them.

The history of slavery goes back far beyond the European colonization of the Caribbean. It emerged soon after the adoption of settled agriculture and should be conceptualized as the extension of the logic of domestication of animals to unfortunate members of our own species.

But there was something new and peculiar about American slavery. For thousands of years, skin color had no bearing on who was seen as a suitable candidate for enslavement. It was in the Americas that people of African origin became associated with servitude for the first time.

The basic principle of slavery was that it was acceptable to enslave anyone who didn’t follow your own religion.

The association between Black Africans and slavery only began in the fifteenth century.

With the Reconquista coming to an end, access to the Black Sea slave markets blocked by the Ottomans, and all the islands except the Canaries uninhabited, they found a variety of alternative sources of forced labor.[15] This included Berbers from northwest Africa and conversos—Iberian Jews and Muslims who had converted to Christianity yet were treated with deep suspicion. But as Spanish and Portuguese merchants developed closer links with West Africa, it became the most reliable source of slaves. In fact, Black Africans were increasingly being transported back to Europe too: by the mid-sixteenth century they constituted over 7 percent of Seville’s population and 10 percent of Lisbon’s.

As West Africa was connected to Europe and Asia by overland and now sea routes, the local population had been exposed to Old World pathogens and fared much better.

The early conquistadors’ decision to use enslaved Africans on their sugar plantations had unexpected but momentous consequences: it inadvertently set the whole of the American tropics on an inescapable path toward racialized slavery because the nascent transatlantic slave trade carried not only people but also some of the mosquitoes and microbes that made West Africa a deadly place for Europeans.

The Caribbean is home to a number of other species of the Anopheles mosquito that were capable of transmitting Plasmodium falciparum. But they are not as effective as their African cousins because they are less drawn to human blood. As a result, malaria—which was the major killer in West Africa—was not as deadly in places like Hispaniola.

The arrival of West African pathogens turned the Caribbean into a new white man’s grave. Yellow fever epidemics rather than malaria were the major killer of Europeans, but the basic outcome was the same: almost everyone who had grown up in West Africa would have been exposed to yellow fever and acquired lifelong immunity, whereas new settlers from Europe hadn’t developed any tolerance and so died in droves.[23] As a result, African labor became the economically “rational” option for plantation owners.

The failure of New Edinburgh didn’t just kill 2,000 people; it also wiped out all the money that had been invested in—or gambled on—this doomed project. Cannily, the English promised to compensate the investors if they agreed to closer ties between the two countries. Even committed Scottish nationalists supported the 1707 Act of Union when faced with the possibility of financial ruin. “Thus,” wrote the historian John McNeill, “Great Britain was born, with the assistance of fevers from Panama.”

Yellow fever killed about 6,000 people, half of the white population of the island, in the mid-seventeenth century.[39] Faced with the loss of so many workers, English plantation owners started to copy the model pioneered by the Spanish and use slave labor from Africa. By the 1680s, enslaved Africans had all but displaced European indentured laborers in the Caribbean.

The transatlantic slave trade created suffering on an almost unimaginable scale. Between the start of the sixteenth and the middle of the nineteenth century, 12.5 million Africans were transported to the Americas—the largest involuntary migration in human history.

There was nothing new about degrading stereotypes of slaves, but in the New World people of African heritage were for the first time exclusively associated with servitude.[45] It is the specifically racial nature of modern American slavery that distinguishes it from pre-modern forms of forced labor. But once Black Africans had become inextricably linked with slavery in the European imagination, modern ideas about race were developed in order to justify this iniquitous situation.

Immanuel Kant, for example, wrote that the “race of the whites contains all talents and motives in itself.” Black Africans, in contrast, “can be educated, but only to the education of servants” or, in other words, “they can be trained.” Native Americans were, according to Kant, “uneducable” and “lazy,” which might have served to soften European guilt for colonizing their continent and literally decimating them. Curtin points out that immunity to infectious diseases was a major factor in these stereotypes. The idea that Black people are well suited to a life of hard labor was influenced by African immigrants’ apparently unique ability to survive on the plantations in tropical regions of the Americas. In contrast, Native Americans were seen as a “weak race” because they often died after their first encounters with “white people.”

The fact that Africans have been present on the continent since 1619 is remarkable: even the Pilgrim Fathers—whose story plays such a central role in American mythology—didn’t get there until the following year.

The first record of what can be recognized as racialized slavery doesn’t appear until 1640, when three indentured laborers from Virginia—two white and one Black—ran away from their place of work. After they were captured, the colony’s highest court sentenced the two Europeans to four additional years of servitude. In contrast, the unfortunate African American—whose name was John Punch—was condemned to “serve his said master or his assigns for the time of his natural Life here or elsewhere.” Still, at the time, John Punch was very much an exception to the rule.

It wasn’t until the end of the seventeenth century that the number of African Americans in North America took off—in both absolute and relative terms. From under 7,000 in 1680 (5 percent of the population), their number increased to almost 17,000 in 1690 (8 percent), 28,000 in 1700 (13 percent), and then kept on growing.[51] By 1750, there were almost a quarter of a million Black people living in the North American colonies, roughly 20 percent of the population. When we look at colony-level statistics, it is clear that the proportion of African Americans barely changed in the northern colonies; the increase in numbers is almost totally accounted for by the southern colonies. By 1700, African Americans represented 43 percent of the population in South Carolina and 28 percent in Virginia, for example. Fifty years later, the numbers were 61 percent and 44 percent respectively.

In fact, the single biggest factor behind the sudden and marked increase in enslaved African Americans between 1680 and 1750 in the southern colonies—but not the northern ones—was infectious diseases. Unlike the Caribbean, where yellow fever was the major hazard, in the North American colonies it was malaria that played a decisive role.

On the American mainland falciparum was transmitted by Anopheles quadrimaculatus, a species of mosquito common in low-lying parts of the east coast. It is not as effective at spreading the plasmodium as its West African “cousins,” but it is better than Caribbean species because of its preference for human blood.[56] So malaria wasn’t as devastating as in West Africa, but it was far more consequential than in the Caribbean.

The climate influenced the distribution of malaria in North America in another important way: as Plasmodium falciparum requires long stretches of relatively warm temperature in order to reproduce, it could survive in the southern colonies but not in the northern ones. In fact, the geographical boundary between areas where the parasite could and couldn’t reproduce falls more or less exactly on the Mason-Dixon Line that divided Maryland from Pennsylvania and Delaware.

Esposito’s analysis of a database of 3,000 Africans sold in the slave markets of Louisiana between 1719 and 1820 shows that those who came from the most malaria-ridden regions of West Africa—who therefore had the highest level of immunity—commanded significantly higher prices than those who did not.

At this point the descendants of settler colonies were capable of working on the land without getting gravely ill, but the die was already cast: there was an entire ideology in place to justify a racialized class system in which it was seen as natural that African Americans toiled on plantations while the white population raked in the profits.

The newly arrived French soldiers were also susceptible to malaria, but because it takes about a month from being bitten by an infected mosquito to the onset of symptoms, they didn’t fall ill until after the British had given up.

Although John McNeill is careful not to completely ignore the role of Great Men like George Washington, he drolly suggests that the female Anopheles quadrimaculatus mosquitoes should be considered one of the “founding mothers of the United States.” As he points out, malaria killed eight times more British troops than American guns.

the Haitian Revolution, the only time in history when enslaved Africans succeeded in overthrowing their European oppressors.

The threat of dying was not high enough to discourage impoverished aristocrats from making a quick livre, but it wasn’t low enough for them to bring their families over and settle down forever. As a result, plantations were run to maximize short-term profit. Nowhere was this more apparent than in the treatment of enslaved Africans. More than half of all enslaved Africans died within five years of arriving in Saint-Domingue—not from yellow fever but from overwork, malnutrition and crowded, unsanitary conditions which made them susceptible to dysentery, typhoid and tetanus.

There was a simple economic reason for the brutal treatment of enslaved Africans: they were cheap to replace—so cheap, in fact, that it was more cost-effective to buy new laborers every few years than to provide them with decent living standards and encourage them to have children.

The short-term economic calculations of plantation owners overlooked the fact that this approach destabilized Saint-Domingue society because it meant the majority of enslaved workers had been born in Africa: they remembered life before servitude, longed to be free again, and recognized that if they didn’t rise up they would most likely be dead within a few years.

While the revolution quickly swept away the remnants of feudalism in France, the white supremacist slave society remained unchanged in the Caribbean colonies. That is, until the Black population of Saint-Domingue took matters into their own hands.

Aedes aegypti was a crucial weapon in their arsenal. The rebels knew from experience that newly arrived Europeans died in droves every summer during the rainy season, when mosquitoes thrived, and they planned to fully utilize the advantage that their immunity to yellow fever offered them.

The insurgents did everything they could to avoid the kind of conventional pitched battle that the French were expecting. They used the rugged terrain to their advantage, launching surprise attacks and then disappearing into the mountainous interior. This not only negated any tactical or technological superiority the colonial army had; it also bought the rebels time until the yellow fever season arrived.[78] It proved to be a wildly effective strategy. When the rains came, the French fell sick in terrifying numbers.

According to John McNeill, a total of 65,000 French troops were sent to reconquer Saint-Domingue. Over 50,000 died, the vast majority from yellow fever. The rebels were, of course, barely affected by the disease. It was as if Makandal really did live on as a mosquito and had returned to finally fulfill his plan to poison the French.