As it does today, malaria played a huge role in the past—a role unlike that of other diseases, and arguably larger. When Europeans brought smallpox and influenza to the Americas, they set off epidemics: sudden outbursts that shot through Indian towns and villages, then faded. Malaria, by contrast, became endemic, an ever-present, debilitating presence in the landscape. Socially speaking, malaria—along with another mosquito-borne disease, yellow fever—tumed the Amelicas upside down. Before these maladies arrived, the most thickly inhabited terrain north of Mexico was what is now the southeastem United States, and the wet forests of Mesoamerica and Amazonia held millions of people. After malaria and yellow fever, these previously salubrious areas became inhospitable. Their former inhabitants fled to safer lands; Europeans who moved into the emptied real estate often did not survive a year. ...

...Tobacco brought malaria to Virginia, indirectly but ineluctably, and from there it went north, south, and west, until much of North America was in its grip. Sugarcane, another overseas import, similarly brought the disease into the Caribbean and Latin America, along with its companion, yellow fever. Because both diseases killed European workers in American tobacco and sugar plantations, colonists imported labor in the form of captive Africans—the human wing of the Columbian Exchange, In sum: ecological introductions shaped an economic exchange, which in turn had political consequences that have endured to the present. 

Unsurprisingly, falciparum thrives in most of Africa but gained a foothold only in the warmest precincts of Europe: Greece, Italy, southern Spain, and Portugal. Vivax, by contrast, became endemic in much of Europe, including cooler places like the Netherlands, lower Scandinavia, and England. From the American point of view, falciparum came from Africa, and was spread by Africans, whereas vivax came from Europe, and was spread by Europeans—a difference with historic consequences. ...

...Consider the seventeenth-century English entrepreneurs who wanted to make money in North America. Because Chesapeake Bay had no gold and silver, the best way to profit was to produce something else that could be exported to the home country. … In Chesapeake Bay, the English settled on tobacco, for which there was huge demand. To satisfy that demand, the colonists wanted to expand the plantation area. To do that, they would have to take down huge trees with hand tools; break up soil under the hot sun; hoe, water, and top the growing tobacco plants; cut the heavy, sticky leaves; drape them on racks to dry; and pack them in hogsheads for shipping. All of this would require a lot of labor, could the colonists acquire it? 

Before answering this question make the assumption, abundantly justified, that the colonists have few moral scruples about the answer and are concerned only with maximizing ease and profit. From this point of view, they had two possible sources for the required workforce: indentured servants from England and slaves from outside of England (Indians or Africans). Servants or slaves: economically speaking, was the best choice?

Indentured servants were contract laborers recruited from England's throngs of unemployed. Because the poor could not afford the costly journey across the sea, planters paid for the voyage and servants paid off the debt by working for a given period, typically four to seven years. After that, indentured servants were free to claim their own land in the Americas. Slavery is harder to define, because it has existed in many different forms. But its essence is that the owner acquires the right to coerce labor from slaves, and slaves never gain the right to leave; they must work and obey until they die or are freed by their owners. Indentured servants are members of society, though at a low rank. Slaves are usually not considered members of society, either because they were born far away or because they somehow have forfeited their social standing, as in the occasional English practice of turning convicts into slaves. 

During the last quarter of the seventeenth century, England chose slaves over servants—indeed, it became the world's biggest slaver. So well nowadays is the English embrace of slavery that the idea of another path is hard to grasp. But in many respects the nation's turn to bondage is baffling—the institution has so many inherent problems that economists have often puzzled over why it exists. More baffling still is the form that bondage took in the Americas: chattel slavery, a regime much harsher than anything seen before in Europe or Africa.

On the simplest level, slaves were more expensive than servants. In a well-known study, Russell R. Menard of the University of Minnesota tallied up the prices in Virginia and Maryland of slaves and servants whose services had to be sold after their masters' deaths. In the last decades of the seventeenth century, the average price of a prime-age male African slave was £25. Meanwhile, the servants' contracts typically cost about £10. … At that time, £25 was a substantial sum: about four year's pay for the typical hired worker in England. The servant was substantially cheaper.

To be sure, servants would eventually be able to leave their master's employ, lowering their value (attempting to take this into account, Menard looked only at servants with more than four years remaining on their contracts). But the longer period of service one could expect from a slave still would not justify slavery economically, the great economist Adam Smith argued. An inherent flaw with slavery, he maintained, is that slaves made unsatisfactory workers. Because they were usually from distant cultures, they often didn't speak their owners' language and could be so unfamiliar with their owners' societies that they would have to be trained from scratch (Africans, for example, knew only tropical forms of agriculture). Worse, they had every incentive to escape, wreak sabotage, or kill their owners, the people who were depriving them of liberty. Indentured servants, by contrast, spoke the same language, accepted the same social norms, and knew the same farming methods. And their contracts were for a limited time, so they cheat). Because willing hands are more likely to do their jobs well, Smith reasoned in The Wealth of Nations, "the work done by freemen comes cheaper in the end than that performed by slaves." All else being equal, he argued, economics suggests that planters should have chosen the cheaper, easier, less threatening alternative: servants from Europe. …

… [But] between 1680 and 1700, the number of slaves suddenly exploded. Virginia's slave population rose in those years from three thousand to sixteen thousand—and kept soaring thereafter. In the same period the tally of indentured servants shrank dramatically. It was a pivot in world history, the time when English America became a slave society and England became the dominant player in the slave trade. 

What accounts for this about-face? … at the very time the supply of [potential indentured servants were] increasing the colonists turned to captive Africans—people who couldn't speak the language, had no wish to cooperate, and cost more to transport. Why? …

…Slavery occurred in most Indian societies, but the institution differed from place to place. Among Algonkian-language societies…slavery was usually a temporary state. Slaves were prisoners of war who were treated as servants until they were either tortured and slain, ransomed back to their original groups, or inducted into [their new] society as full members. … Economically speaking, indigenous slavery was a good deal for both natives and newcomers. In the Charleston market Indians sometimes could sell a single slave for the same price as 160 deerskins. "One slave brings a Gun, ammunition, horse, hatchet, and a suit of Cloathes, which would not be procured without much tedious toil a hunting," a Carolina slave buyer noted, perhaps with some exaggeration, in 1708. "The good prices The English traders give them for slaves Encourages them to this trade Extreamly."

"Good prices" from the Indian point of view, but cheap to the English. Indian captives cost £5-10, as little as half the price of indentured servants… More important, the annual cost of ownership was much lower, because slaves did not have to be released after a few years—the purchase price could be amortized over decades. Unsurprisingly, the colonists chose Indian slaves over European servants. A 1708 census, Carolina's first, found four thousand English colonists, almost 1,500 Indian slaves, and just 160 servants, the majority presumably indentured. … For its first four decades the colony was mainly a slave exporter…

In any case, the Indian slave trade was immensely profitable—and very short-lived. By 1715 it had almost vanished, a victim in part of its own success. As Carolina's elite requested more and more slave raids, the Southeast became engulfed in warfare, destabilizing all sides. Victimized Indian groups acquired guns and attacked Carolina in a series of wars that the colony barely survived. Working in groups, Indian slaves proved to be unreliable, even dangerous employees who used their knowledge of the terrain against their owners. Rhode Island denounced the "conspiracies, insurrections, rapes, thefts and other execrable crimes" committed by captive Indian laborers, and banned their import. So did Pennsylvania, Connecticut, Massachusetts, and New Hampshire. The Massachusetts law went out of its way to excoriate the "malicious, surly and revengeful" Indian slaves. 

The worst problem, though, was something else. As in Virginia, malaria came to Carolina. At first the English had extolled the colony's salubrious climate. Carolina, one visitor wrote, has "no Distempers either Epidemical or Mortal"; colonists' children had "Sound Constitutions, and fresh ruddy complexions." The colonists decided to use the warm climate to grow rice, then scarce in England. Soon after came reports of "fevar and ague"—rice paddies are notorious mosquito havens. Falciparum had entered the scene, accompanied a few years later by yellow fever. Cemeteries quickly filled. In some parishes, more than three out of four colonists' children perished before the age of twenty. As in Virginia, almost half of the deaths occurred in the fall. (One German visitor's summary: "in the spring a paradise, in the summer a hell, and in the autumn a hospital.") 

Unfortunately, Indians were just as prone to malaria as English indentured servants—and more vulnerable to other diseases. Native people died in ghastly numbers…

[In the] early 1970s…collaborators at the National Institutes of Health’s Laboratory of Parasitic Disease…asked seventeen men, all volunteers, to put their arms into boxes full of mosquitoes. … Each man was bitten dozens of times…twelve men came down with the disease. (The researchers quickly treated them.) The other five had not a trace of the parasite in their blood. … The volunteers were Caucasian and African American. Every Caucasian came down with malaria. Every man who didn’t get malaria was…African American. …

[The research team believe that this] inherited malaria resistance occurs in many parts of the world, but the peoples of West and Central Africa have more than anyone else—Inherited malaria resistance occurs in many parts of the world, but the peoples of West and Central Africa have more than anyone else—they are almost completely immune to vivax, and (speaking crudely) about half-resistant to falciparum. Add in high levels of acquired resistance from repeated childhood exposure, and adult West and Central Africans were and are less susceptible to malaria than anyone else on earth. Biology enters history when one realizes that almost all of the slaves ferried to the Americas came from West and Central Africa. In vivax-ridden Virginia and Carolina, they were more likely to survive and produce children than English colonists. Biologically speaking, they were fitter, which is another way of saying that in these places they were—loaded words! —genetically superior. …

…Philip Curtin, one of slavery's most important historians, burrowed in British records to find out what happened to British soldiers in places like Nigeria and Namibia. The figures were amazing: nineteenth-century parliamentary reports on British soldiers in West Africa concluded that disease killed between 48 percent and 67 percent of them every year. The rate for African troops in the same place, by contrast, was about 3 percent, an order-of-magnitude difference. African diseases slew so many Europeans, Curtin discovered, that slave ships often lost proportionately more white crewmen than black slaves—this despite the horrendous conditions belowdecks, where slaves were chained in their own excrement. To forestall losses, European slavers hired African crews. …

Malaria did not cause slavery. Rather, it strengthened the economic case for it... little evidence exists that the first slave owners clearly understood African immunity, partly because they didn't know what malaria was and partly because people in isolated plantations could not easily make overall comparisons. Regardless of whether they knew it, though, planters with slaves tended to have an economic edge over planters with indentured servants. If two Carolina rice growers brought in ten workers apiece and one ended up after a year with nine workers and the other ended up with five, the first would be more likely to flourish. Successful planters imported more slaves. Newcomers imitated the practices of their most prosperous neighbors. The slave trade took off, its sails filled by the winds of Plasmodium.