The Columbian Exchange

Summary

When Columbus reached the Americas in 1492, he ended more than ten thousand years of near-total separation between two halves of the planet. What followed was one of the largest transfers of living things in recorded history: diseases, plants, animals, and people moving in both directions across the Atlantic. The historian Alfred W. Crosby coined the phrase “Columbian Exchange” in 1972 to describe this process. It brought smallpox to populations with no immunity to it, carried New World food crops to Europe, Asia, and Africa, and set off a global population surge that continues today. The exchange was not symmetrical. Old World diseases crossed to the New World with catastrophic force; very few American diseases traveled the other direction. The result was a biological transformation that reshaped human populations, ecologies, and food systems on a scale matched only by the end of the last ice age.

The Biological Divide

For the ten millennia before 1492, the Americas and Eurasia had developed along entirely separate biological lines. Crosby argues that Columbus’s landfall renewed a connection “as significant as the Bering land bridge had once been,” ending what had been, apart from sparse Viking voyages and scattered contacts, a near-total isolation.(Alfred W. Crosby, 1972) The trend toward biological homogeneity set in motion that year is, in Crosby’s assessment, “one of the most important aspects of the history of life on this planet since the retreat of the continental glaciers.”(Alfred W. Crosby, 1972) Crosby’s central argument is that the most important changes wrought by Columbus’s voyages were biological in nature, a fact obvious to ecologists and geographers but missed by most traditional historians, who had trained their attention on conquest, trade, and political transformation.(Alfred W. Crosby, 1972)

The separation left visible marks. American flora remained highly distinctive even after centuries of post-Columbian contact: only about 18 percent of plant species in northeastern North America were of non-American origin as late as the twentieth century.(Alfred W. Crosby, 1972) The faunal record told a stranger story. Both the horse and the camel originated in North America, migrated into Asia and beyond, and then went extinct in their homeland during the Pleistocene.(Alfred W. Crosby, 1972) The continent that would send horses to the world had none of its own when the Spanish arrived. The isolation also left a medical signature: American Indians are the most biologically uniform major human population, showing a degree of genetic uniformity that anthropologists who have compared the blood type distributions of the Americas with the striking diversity found among peoples of the eastern hemisphere find difficult to account for by any means other than descent from a small founding group.(Alfred W. Crosby, 1972)

The ancestors of the American Indians crossed into the New World before agriculture had been invented, and certainly before the people of Siberia had taken it up, entering isolation before major animal domestications had been accomplished.(Alfred W. Crosby, 1972) The resulting population was genetically uniform to a degree remarkable for its size: blood type maps of the Americas show near-universal Type O across the whole continent, a uniformity that led the physical anthropologist T. D. Stewart to conclude that no comparable population had remained so uniform after expanding over such a large area.(Alfred W. Crosby, 1972)

This uniformity was not simply a curiosity. It reflected a founding bottleneck, a population descended from a small group that had passed through the cold filter of the Siberian corridor and Alaska. That passage had medical consequences. As Crosby explains, the cold of the land bridge and the rigors of life in those latitudes screened out many diseases, eliminating anyone suffering from debilitating illness before they could enter the Americas.(Alfred W. Crosby, 1972) The people who arrived in the New World carried a narrowed selection of pathogens and, over millennia of isolation, developed immunological experience with only that limited local set. As Crosby states, when Columbus reconnected the hemispheres, the American Indian met for the first time his most hideous enemy — not the white man nor his black servant, but the invisible killers which those men brought with them from the Old World.(Alfred W. Crosby, 1972) The Bering land bridge through which the ancestors of the American Indians passed was approximately 1,500 kilometers wide from north to south when exposed; had the water level today fallen only forty meters, the Bering Strait would again be dry land.(Alfred W. Crosby, 1972)

Disease and Demographic Catastrophe

The concept Crosby places at the center of his argument is what epidemiologists call the virgin soil epidemic: a disease outbreak in a population with no prior exposure to a pathogen, and therefore no acquired immunity to it. Crosby identifies the American Indian as probably the longest-isolated major human division from the rest of mankind, with the possible exception of the Australian Aboriginal peoples.(Alfred W. Crosby, 1972) When contact came, the consequences were correspondingly severe.

In Mexico and Peru between 1520 and 1600, the historical record shows something like fourteen epidemics in the former and perhaps seventeen in the latter.(Alfred W. Crosby, 1972) To understand why these epidemics hit so hard, the biology of smallpox matters. The virus is transmitted through air via droplets or dust; it can infect a visitor who merely breathes the air in a room with an ill person. There are no long-term carriers and no animal reservoir; it must pass from person to person.(Alfred W. Crosby, 1972) Among unvaccinated populations, case mortality runs approximately 30 percent. When smallpox first appeared in Iceland in 1707, 18,000 of the island’s 50,000 inhabitants died within two years.(Alfred W. Crosby, 1972)

The first pandemic in the New World began in December 1518 or January 1519 in Santo Domingo, brought from Castile. According to the historian Bartolomé de Las Casas, it left no more than one thousand alive of the vast population he had himself seen on the island.(Alfred W. Crosby, 1972) The same wave reached Central America and almost certainly Peru, causing what one expert called “in all likelihood the most severe single loss of aboriginal population that ever occurred.”(Alfred W. Crosby, 1972)

The military consequences were direct. A black man traveling with the Narvaez expedition brought smallpox to Mexico; he infected the household in Cempoala where he was quartered, and it spread from there through the entire country because, as a Spanish eyewitness reported, the Indians “being so numerous and eating and sleeping together, quickly infected the whole country.”(Alfred W. Crosby, 1972) The resulting sixty-day epidemic in Tenochtitlan gave Cortés the respite he needed to regroup after the Noche Triste. Crosby is blunt about the implication: had there been no epidemic, the Aztecs could have pursued the Spaniards, and Cortés might have ended his life under an obsidian blade.(Alfred W. Crosby, 1972) The Aztec lord Cuitlahuac, who had directed the most dangerous attacks on the Spanish retreat, died of smallpox before the final siege.(Alfred W. Crosby, 1972)

Demographic estimates for central Mexico show a population drop from about 25 million on the eve of conquest to 16.8 million within a decade, figures compiled by historians Sherburne F. Cook and Woodrow Borah.(Alfred W. Crosby, 1972) In Peru, an epidemic triggered a succession crisis that killed the Inca Huayna Capac and his designated heir Ninan Cuyoche, leading to a civil war between Huascar and Atahualpa that left the empire fatally divided.(Alfred W. Crosby, 1972) Pedro Pizarro wrote afterward that without that division, a thousand Spaniards would not have been enough to conquer the land.(Alfred W. Crosby, 1972)

Why did disease outpace the armies? Because biologically defenseless Indians made more efficient carriers of smallpox than the Spaniards.(Alfred W. Crosby, 1972) An Indian who received news of the approaching Europeans could just as easily have received the infection; the disease traveled faster than any army.

Indigenous accounts confirm the scale of the catastrophe. A Yucatan Indian wrote of the time before European arrival: “There was then no sickness; they had no aching bones; they had then no high fever; they had then no smallpox; they had then no burning chest; they had then no abdominal pain; they had then no consumption; they had then no headache. At that time the course of humanity was orderly. The foreigners made it otherwise when they arrived here.”(Alfred W. Crosby, 1972) The Cakchiquel Maya account from Guatemala in 1520-21 describes total social breakdown: “Great was the stench of the dead. After our fathers and grandfathers succumbed, half of the people fled to the fields. The dogs and vultures devoured the bodies… We were born to die!”(Alfred W. Crosby, 1972)

The contrast with Africans transported as slaves is telling. McNeill notes that when Africans began arriving in the New World after 1500, they suffered no spectacular die-off from European diseases — sufficient demonstration that African populations had maintained exposure to the standard childhood diseases of Eurasian civilization.(McNeill, 1976) American Indian populations lacked that exposure history entirely.(McNeill, 1976) English settlers at Roanoke in 1587 supplied early direct testimony to this vulnerability: after their departure from every Indian village where hostility had been shown, the people began to die very fast, so that in some villages sixty died within a short time while those who had never come near the English remained healthy.(Alfred W. Crosby, 1972)

Measles provides a parallel illustration of virgin soil dynamics: when measles first reached the Fiji Islands in 1875, it killed 40,000 people in a population of about 150,000.(Zinsser, 1935)

The Syphilis Debate

Crosby writes that syphilis is the most “uniquely historical” of mankind’s important maladies because it has a beginning: Ulrich von Hutten wrote in the early sixteenth century that “In the yere of Chryst 1493 or there aboute this most foule and most grevous dysease beganne to sprede amonge the people.”(Alfred W. Crosby, 1972)

The case for an American origin rests on several lines of evidence. Ruy Diaz de Isla, a Spanish physician, claimed in a 1539 book that he had treated Columbus’s men who had contracted syphilis in America in 1492 and had personally observed its rapid spread through Barcelona; he named it Morbo Serpentino and described it as a new affliction entirely.(Alfred W. Crosby, 1972) No unequivocal description of syphilis appears in any pre-Columbian Old World literature. Galen, Avicenna, and other classical and medieval clinicians, accomplished describers of surface symptoms, left nothing recognizable as syphilis. No Chinese writer has ever cited ancient texts as describing the disease, despite China’s strong tradition of quoting from the classics.(Alfred W. Crosby, 1972) The paleopathologist Elliott Smith examined approximately 30,000 bodies of ancient Egyptians and Nubians representing every period of the last sixty centuries and stated “quite confidently that no trace whatever, even suggesting syphilitic injuries to bones or teeth, was revealed in Egypt before modern times.”(Alfred W. Crosby, 1972) Pre-Columbian American bones, by contrast, do show syphilitic damage: one researcher described the deformation of forehead bones in some skeletons as “as unambiguously syphilitic in origin as a positive Wassermann reaction.”(Alfred W. Crosby, 1972)

The naming pattern across cultures reinforces the impression of novelty. Italians called syphilis the French disease; the French called it the disease of Naples; Russians called it the Polish disease; Chinese called it the ulcer of Canton; Japanese called it the disease of the Portuguese.(Alfred W. Crosby, 1972) Nearly every nation assigned the disease to a neighbor, and the word “syphilis,” coined by Fracastoro in the 1520s, did not become standard until the nineteenth century. The two most important historians of the early Spanish empire, Las Casas and Oviedo, both state that Columbus brought syphilis back from America. Las Casas personally asked Indians whether they had known the disease before Europeans came; they told him they had suffered from it “beyond all memory.” Both historians noted that the disease was far less dangerous for infected Indians than for Spaniards, the pattern one would expect if one population had long contact with the disease and the other none at all.(Alfred W. Crosby, 1972)

The first recorded epidemic of syphilis took place in Italy in 1494-1495, when Charles VIII of France invaded Naples with an army of about 50,000 soldiers.(Alfred W. Crosby, 1972) Syphilis, which had been spreading slowly and quietly across Europe, flared into epidemic during this invasion.(Alfred W. Crosby, 1972) When Charles disbanded his army at Lyon in November 1495, its members scattered to a dozen lands, making the lightning advance of syphilis across Europe inevitable.(Alfred W. Crosby, 1972) By the summer of 1495 it had appeared in Germany; by 1496 in Holland, England, and Greece; by 1499 in Hungary and Russia; by 1498 in India; and by 1505 in Canton.(Alfred W. Crosby, 1972) Crosby’s summary: “In a decade it advanced from the Caribbean to the China Sea.”(Alfred W. Crosby, 1972)

The alternative account is the Unitarian theory, championed by E. H. Hudson.(Alfred W. Crosby, 1972) On this view, venereal syphilis is one syndrome of a single worldwide disease (treponematosis) that also manifests as yaws in the tropics, bejel in the Middle East, pinta in Central America, and irkinja in Australia.(Alfred W. Crosby, 1972) The organisms causing these conditions cannot be distinguished under a microscope, and immunity to one confers immunity to all.(Alfred W. Crosby, 1972)

Zinsser, writing earlier than Crosby, noted that the short interval between Columbus’s return in 1493 and the Naples epidemic of 1495 is the main objection to the Columbian theory: there may not have been enough time for the disease to spread from sailors to epidemic proportions across Europe.(Zinsser, 1935) Crosby, having weighed both theories, concludes that the Columbian theory “is still viable”: the only pre-Columbian bones clearly displaying treponematosis lesions are American, and contemporaries did record the return of venereal syphilis with Columbus’s men, testimony that “cannot be shrugged off.”(Alfred W. Crosby, 1972)

The early form of syphilis in Europe was far more virulent than what we know today.(Alfred W. Crosby, 1972) Von Hutten described the initial outbreak: dark green pustules so disfiguring that “the slight therof was more grevous unto the pacient then the peyne it selfe,” pain as if lying in fire.(Alfred W. Crosby, 1972) He noted this extreme form lasted about seven years before the disease became less “fylthy.”(Alfred W. Crosby, 1972) The physician Jean Astruc analyzed five stages from 1494 to 1610, showing progressive attenuation: the earliest phase brought widespread rashes, destruction of the palate and jaw, large tumors, agonizing pains, and often early death; by 1560-1610 the deadliness had declined substantially.(Alfred W. Crosby, 1972)

Mercury was the only generally effective treatment for four hundred years after 1493, its toxicity causing patients to drool several pints of saliva daily along with gums, teeth, and internal tissues. Guaiacum, a decoction of West Indian wood, became the most popular panacea of the 1520s, but its reputation evaporated within a decade, though it remained in the British Pharmacopoeia until 1932.(Alfred W. Crosby, 1972)

Plant Transfers

Columbus’s second voyage in 1493 brought seeds and cuttings for wheat, chickpeas, melons, onions, radishes, salad greens, grape vines, sugar cane, and fruit trees. The transformation of New World agriculture was well under way by 1500 and, Crosby argues, irrevocable in both North and South America by 1550.(Alfred W. Crosby, 1972) Sugar cane arrived with that same voyage; by the late 1530s there were thirty-four mills on Espanola, and sugar had become one of the island’s two economic staples.(Alfred W. Crosby, 1972) The banana reached Espanola from the Canaries in 1516 and multiplied so rapidly that within a decade it was marvellous in its abundance across the islands and in Tierra Firme.(Alfred W. Crosby, 1972)

Non-intentional weed migration was equally pervasive. Seeds arrived in the folds of textiles, in clods of mud, in animal dung. By the twentieth century, an American botanist could walk through whole meadows and find not a single plant species that had grown in America before Columbus. Kentucky bluegrass, daisies, and dandelions are all Old World in origin.(Alfred W. Crosby, 1972)

The botanist Nikolai Vavilov identified the 640 most important cultivated plants in the world: roughly 500 Old World, 100 New World.(Alfred W. Crosby, 1972) Yet Crosby concludes that the American 100, taken together, “made the most valuable single addition to the food-producing plants of the Old World since the beginnings of agriculture.”(Alfred W. Crosby, 1972)

The caloric arithmetic explains why. Maize yields per unit of land roughly double that of wheat on world average, and prospers in zones too dry for rice and too wet for wheat, occupying a niche no Old World grain could fill.(Alfred W. Crosby, 1972) The potato produces several times the food per unit of land as wheat and can be cultivated on small plots of poor soil at altitudes from sea level to over 10,000 feet.(Alfred W. Crosby, 1972) Manioc, at 9.9 million calories per hectare, surpasses all others and grows on land too infertile for almost any other crop.(Alfred W. Crosby, 1972) The full comparison: manioc 9.9, sweet potatoes 7.1, potatoes 7.5, maize 7.3 million calories per hectare, against wheat 4.2, rice 3, barley 5.1, oats 5.5 million.(Alfred W. Crosby, 1972)

By 1963, the potato was the largest crop in the world at 277.6 million metric tons, with maize at 251.9 million. Crosby estimates that something like one third of all plant food raised to feed humans and their animals globally now comes from plants of American origin.(Alfred W. Crosby, 1972)

The chile pepper, virtually unknown in seventeenth-century India, spread to become “the nearly indispensable ingredient in every Indian meal” by the twentieth century, serving, as one observer wrote, as “the only seasoning which the millions of poor can obtain to eat with their rice.”(Alfred W. Crosby, 1972)

Africa’s dependence on American crops is more visible than any other continent’s. Maize was under cultivation in West Africa by at least the second half of the sixteenth century. Nigeria produces more manioc than any other food; one authority estimated Africa accounts for roughly 50 percent of world manioc production and 50 percent of its sweet potatoes and yams.(Alfred W. Crosby, 1972) In China, American food plants rose from virtually zero to approximately 20 percent of total national food production over three centuries, a shift that Ping-ti Ho credits with making possible the continued growth of population as rice culture approached its limits.(Alfred W. Crosby, 1972)

Animal Transfers

Columbus brought the first contingent of horses, dogs, pigs, cattle, chickens, sheep, and goats to Espanola on his second voyage in 1493, restoring horses to the Americas for the first time since the Pleistocene extinctions.(Alfred W. Crosby, 1972) Crosby characterizes the European introduction of Old World plants and animals to the New World as probably the greatest biological revolution in the Americas since the end of the Pleistocene era, with the Iberian livestock that spread across North and South America transforming ecologies at a pace that dwarfed every previous post-glacial ecological change.(Alfred W. Crosby, 1972) Without American diseases to check them, and with access to rich grasses and fruits, these animals reproduced rapidly.(Alfred W. Crosby, 1972)

The numbers are stark. The thirteen pigs Columbus brought to Cuba had grown to 30,000 by April 1514, according to Diego Velasquez.(Alfred W. Crosby, 1972) Hernando De Soto took thirteen pigs to Florida in 1539 and still had several hundred at his death three years later, having eaten them only in dire emergencies. By 1579, some ranches in northern Mexico maintained herds of 150,000 cattle, with 20,000 considered a small herd; two ranches on the Zacatecas-Durango border branded a combined 75,000 calves in 1586 alone.(Alfred W. Crosby, 1972) Wild horses on the Argentine pampas multiplied until, one observer wrote, the plains looked “like woods from a distance.”(Alfred W. Crosby, 1972)

The ecological competition between introduced livestock and Indian populations was direct and often unacknowledged. Indian civilizations in Mexico and Peru rested primarily on vegetable diets, which meant anything affecting croplands affected the people.(Alfred W. Crosby, 1972) Cattle and horses did not merely occupy grazing land; they invaded croplands and competed directly for ground that had fed Indian communities.

The horse had one further effect that cuts across the usual narrative of destruction: it enabled certain Indian cultures to flourish briefly on their own terms. By the late eighteenth century, the Plains Indians — Blackfoot, Arapaho, Cheyenne, Crow, Sioux, Comanche — had adopted the horse and built an equestrian culture of remarkable scope. That culture lasted three or four generations before ending with the destruction of the buffalo herds and the catastrophic wars with the United States Army.(Alfred W. Crosby, 1972)

For the native camelids of Peru, the story was simpler. European livestock transmitted a devastating selection of animal diseases to llamas and alpacas, whose populations diminished after the conquest as spectacularly as the Indian population, and for largely the same reasons: disease and brutal exploitation.(Alfred W. Crosby, 1972)

Demographic Consequences

The post-Columbian population history of the world divides into two stories running in opposite directions: collapse in the Americas, expansion everywhere else.

The expansion is extraordinary. World population approximately quadrupled in the three hundred years after the Columbian exchange, from 545 million in 1650 to 2,454 million in 1950. Crosby places this alongside only two earlier episodes of comparable global growth: the development of tools and the invention of agriculture.(Alfred W. Crosby, 1972) New World food plants were the enabling condition. American crops’ decisive advantage was that they made different demands on soils and weather than Old World crops: they occupied land previously rated as useless because of sandiness, altitude, or aridity, producing food where nothing had grown before.(Alfred W. Crosby, 1972)

The Irish case is the sharpest illustration of dependence and fragility both. The Irish population grew from 3.2 million in 1754 to nearly 8.2 million in 1845, sustained almost entirely by the potato. Then came the blight, the failure of that single staple, and one of the worst famines of the modern era.(Alfred W. Crosby, 1972) Java’s population grew from 4.6 million in 1815 to nearly 62.5 million in 1960, and between 1900 and 1940 its diet shifted measurably toward American foods.(Alfred W. Crosby, 1972)

The collapse in the Americas drove a second demographic transformation: the slave trade. With millions of Native Americans dying from disease, violence, and exploitation in the sixteenth through eighteenth centuries — most severely in the coastal and tropical regions where the European diseases swept most completely — plantation labor shortfalls became acute. Europeans could not supply themselves in sufficient numbers, so they turned to Africa.(Alfred W. Crosby, 1972) Between 8 million and 10.5 million Africans were brought to the Americas as slaves, almost all arriving before 1850; 38 percent went to Brazil and 42 percent to the Antilles.(Alfred W. Crosby, 1972)

From 1851 to 1960, over 61 million Europeans migrated to continents other than their birth continent; the great bulk — 45 million by 1924 — migrated to the Americas, of whom approximately 34 million chose the United States, making the Americas the destination for the largest voluntary human migration in recorded history.(Alfred W. Crosby, 1972) The long-run consequence of these migrations is visible in population composition. As of the 1950s, the United States was over 85 percent of European ancestry; Argentina 99.1 percent; Uruguay 96 percent; Brazil 42 percent. Crosby’s summary formulation: “There are two Europes, as there are two Africas: one on either side of the Atlantic.”(Alfred W. Crosby, 1972)

The Exchange Continues

Crosby is explicit that the Columbian exchange is not a historical event with a defined endpoint. It is an ongoing process.

Old World diseases continued to reach isolated populations well into the twentieth century. Between 1871 and 1947, the total native population of Tierra del Fuego dropped from between 7,000 and 9,000 to 150, many of them killed by measles, which remained one of the chief killers of the aborigines of the Chaco.(Alfred W. Crosby, 1972) In 1929, African anopheles mosquitoes arrived in Brazil. They could breed in conditions where American mosquitoes could not, and hundreds of thousands of people fell sick and about 20,000 died before the insects were eliminated.(Alfred W. Crosby, 1972)

The flows moved in both directions. The American gray squirrel was nearly driving Britain’s red squirrels off the island within seventy years of its introduction. The carp, successfully introduced to America in 1877, spread explosively, displacing native fish and waterfowl from ponds, lakes, and rivers. The Colorado potato beetle followed the potato across the Atlantic around 1920 and had advanced as far east as Russia by 1955.(Alfred W. Crosby, 1972)

Native New World diseases proved harder to export. Verruga Peruana remains confined to Peru, Colombia, and Ecuador; Oroya fever stays within a handful of Andean nations; Rocky Mountain spotted fever has never established itself in the Old World.(Alfred W. Crosby, 1972) The asymmetry of disease exchange that so devastated American Indian populations in the sixteenth century persists in the structure of what crossed and what did not. Syphilis, however, stands as the conspicuous exception to this asymmetry: Treponema pallidum is, in Crosby’s formulation, the most important pathological organism that America ever exported, having spread to every part of the world since the fifteenth century and counting among its victims men of high and low estate alike.(Alfred W. Crosby, 1972)

The ecological legacy of the exchange is equally permanent. Old World life forms — grasses, weeds, feral livestock — have transformed vast areas of the Americas so thoroughly that native animals such as the bighorn sheep have been driven back into remote mountain refuges where the competition from introduced species is less intense, and the prairies and pampas that once supported indigenous fauna are now dominated by Old World grasses and the descendants of European livestock.(Alfred W. Crosby, 1972)

Crosby’s final assessment of the biological balance sheet is somber. Man and his imported plants and animals have caused the extinction of more species in the last four hundred years than the ordinary processes of evolution might have killed off in a million. The result of the Columbian exchange, in his view, is “not a richer but a more impoverished genetic pool,” and the impoverishment will increase.(Alfred W. Crosby, 1972)