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The Columbian Exchange
by J.R. McNeill
http://www.learnnc.org/lp/editions/nchist-twoworlds/
The arrival of Christopher Columbus in the Americas marked the meeting of previously separate biological worlds. (John Vanderlyn, Landing of Columbus. Commissioned 1836/1837; placed 1847. Capitol Rotunda, Washington, D.C
Geologists believe that between 280 million and 225 million years ago, the earth’s previously
separate land areas became welded into a landmass called Pangaea. About 120 million years ago,
they believe, this landmass began to separate. As this happened, the Atlantic Ocean formed,
dividing the Americas from Africa and Eurasia. Over the course of the next several million years
in both the Americas and in Afro-Eurasia, biological evolution followed individual paths,
creating two primarily separate biological worlds. However, when Christopher Columbus and his
crew made land in the Bahamas in October 1492, these two long-separated worlds were reunited.
Columbus’ voyage, along with the many voyages that followed, disrupted much of the biological
segregation brought about by continental drift.
After Columbus’ arrival in the Americas, the animal, plant, and bacterial life of these two worlds
began to mix. This process, first studied comprehensively by American historian Alfred Crosby,
was called the Columbian Exchange. By reuniting formerly biologically distinct land masses, the
Columbian Exchange had dramatic and lasting effects on the world. New diseases were
introduced to American populations that had no prior experience of them. The results were
devastating. These populations also were introduced to new weeds and pests, livestock, and pets.
New food and fiber crops were introduced to Eurasia and Africa, improving diets and fomenting
trade there. In addition, the Columbian Exchange vastly expanded the scope of production of
some popular drugs, bringing the pleasures — and consequences — of coffee, sugar, and tobacco
use to many millions of people. The results of this exchange recast the biology of both regions
and altered the history of the world.
The flow from east to west: Disease
By far the most dramatic and devastating impact of the Columbian Exchange followed the
introduction of new diseases into the Americas. When the first inhabitants of the Americas
arrived across the Bering land bridge between 20,000 and 12,000 years ago, they brought few
diseases with them. Why? For one reason, they had no domesticated animals, the original source
of human diseases such as smallpox and measles. In addition, as they passed from Siberia to
North America, the first Americans had spent many years in extreme cold, which eliminated
many of the disease-causing agents that might have traveled with them. As a result, the first
Americans and their descendants, perhaps 40 million to 60 million strong by 1492, enjoyed
freedom from most of the infectious diseases that plagued populations in Afro-Eurasia for
millennia. Meanwhile, in Asia and Africa, the domestication of herd animals brought new
diseases spread by cattle, sheep, pigs, and fowl.
Soon after 1492, sailors inadvertently introduced these diseases — including smallpox, measles,
mumps, whooping cough, influenza, chicken pox, and typhus — to the Americas. People who
lived in Afro-Eurasia had developed some immunities to these diseases because they had long
existed among most Afro-Eurasian populations. However, the Native Americans had no such
immunities. Adults and children alike were stricken by wave after wave of epidemic, which
produced catastrophic mortality throughout the Americas. In the larger centers of highland
Mexico and Peru, many millions of people died. On some Caribbean islands, the Native
American population died out completely. In all, between 1492 and 1650, perhaps 90 percent of
the first Americans had died.
This loss is considered among the largest demographic disasters in human history. By stripping
the Americas of much of the human population, the Columbian Exchange rocked the region’s
ecological and economic balance. Ecosystems were in tumult as forests regrew and previously
hunted animals increased in number. Economically, the population decrease brought by the
Columbian Exchange indirectly caused a drastic labor shortage throughout the Americas, which
eventually contributed to the establishment of African slavery on a vast scale in the Americas.
By 1650, the slave trade had brought new diseases, such as malaria and yellow fever, which
further plagued Native Americans.
The flow from east to west: Crops and animals
Oranges, now a staple of the Florida economy, didn’t grow in the Americas until after the arrival of Spanish explorers
Cattle, sheep, pigs, and goats also proved popular in the Americas. Within 100 years after
Columbus, huge herds of wild cattle roamed many of the natural grasslands of the Americas.
Wild cattle, and, to a lesser degree, sheep and goats, menaced the food crops of Native
Americans, notably in Mexico. Eventually ranching economies emerged, based variously on
cattle, goats, or sheep. The largest ranches emerged in the grasslands of Venezuela and
Argentina, and on the broad sea of grass that stretched from northern Mexico to the Canadian
prairies. Native Americans used the livestock for meat, tallow, hides, transportation, and hauling.
Altogether, the suite of domesticated animals from Eurasia brought a biological, economic, and
social revolution to the Americas.
The flow from west to east: Disease
In terms of diseases, the Columbian Exchange was a wildly unequal affair, and the Americas got the worst of it. The flow of disease from the Americas eastward into Eurasia and Africa was either trivial or consisted of a single important infection. Much less is known about pre-Columbian diseases in the Americas than what is known about those in Eurasia. Based on their study of skeletal remains, anthropologists believe that Native Americans certainly suffered from arthritis. They also had another disease, probably a form of tuberculosis that may or may not have been similar to the pulmonary tuberculosis common in the modern world. Native Americans also apparently suffered from a group of illnesses that included two forms of syphilis. One controversial theory asserts that the venereal syphilis epidemic that swept much of Europe beginning in 1494 came from the Americas; however, the available evidence remains inconclusive.
The flow from west to east: Crops and cuisine
Maize has become a dietary staple in southern Africa
America’s vast contribution to Afro-Eurasia in terms of new plant species and cuisine, however, transformed life in places as far apart as Ireland, South Africa, and China. Before Columbus, the Americas had plenty of domesticated plants. By the time Columbus had arrived, dozens of plants were in regular use, the most important of which were maize (corn), potatoes, cassava, and various beans and squashes. Lesser crops included sweet potato, papaya, pineapple, tomato, avocado, guava, peanuts, chili peppers, and cacao, the raw form of cocoa. Within 20 years of Columbus’ last voyage, maize had established itself in North Africa and perhaps in Spain. It spread to Egypt, where it became a staple in the Nile Delta, and from there to the Ottoman Empire, especially the Balkans. By 1800, maize was the major grain in large parts of what is now Romania and Serbia, and was also important in Hungary, Ukraine, Italy, and southern France. It was often used as animal feed, but people ate it too, usually in a porridge or bread. Maize appeared in China in the 16th century and eventually supplied about one-tenth of the grain supply there. In the 19th century it became an important crop in India. Maize probably played its greatest role, however, in southern Africa. There maize arrived in the 16th century in the context of the slave trade. Southern African environmental conditions, across what is now Angola, Zambia, Zimbabwe, Mozambique, and eastern South Africa, suited maize handsomely. Over the centuries, maize became the primary peasant food in much of southern Africa. In late 20th-century South Africa, for example, maize grew in two-thirds to three-quarters of the region’s cropland.
Despite maize’s success, the humble potato probably had a stronger impact in improving the food supply and in promoting population growth in Eurasia. The potato had little impact in Africa, where conditions did not suit it. But in northern Europe the potato thrived. It had the most significant effect on Ireland, where it promoted a rapid population increase until a potato blight ravaged the crop in 1845, bringing widespread famine to the area. After 1750, Scandinavia, the Low Countries, Germany, Poland, and Russia also gradually accepted the potato, which helped drive a general population explosion in Europe. This population explosion may have laid the foundation for world-shaking developments such as the Industrial Revolution and modern European imperialism. The potato also fed mountain populations around the world, notably in China, where it encouraged settlement of mountainous regions.
Cassava root. Photo by David Monniaux, 2005
While maize and potatoes had the greatest world historical importance of the American crops, lesser crops made their marks as well. In West Africa, peanuts and cassava provided new foodstuffs. Cassava, a tropical shrub native to Brazil, has starchy roots that will grow in almost any soil. In the leached soils of West and Central Africa, cassava became an indispensable crop. Today some 200 million Africans rely on it as their main source of nutrition. Cacao and rubber, two other South American crops, became important export items in West Africa in the 20th century. The sweet potato, which was introduced into China in the 1560s, became China’s third most important crop after rice and wheat. It proved a useful supplement to diets throughout the monsoon lands of Asia. Indeed, almost everywhere in the world, one or another American food crops caught on, complementing existing crops or, more rarely, replacing them. By the late 20th century, about one-third of the world’s food supply came from plants first cultivated in the Americas. The modern rise of population surely would have been slower without them.
