Columbian Exchange, the largest part of a more general process of biological globalization that followed the transoceanic voyaging of the 15th and 16th centuries. Ecological provinces that had been torn apart by continental drift millions of years ago were suddenly reunited by oceanic shipping, particularly in the wake of Christopher Columbus’s voyages that began in 1492. The consequences profoundly shaped world history in the ensuing centuries, most obviously in the Americas, Europe, and Africa. The phrase “the Columbian Exchange” is taken from the title of Alfred W. Crosby’s 1972 book, which divided the exchange into three categories: diseases, animals, and plants.
Diseases
Before 1492, Native Americans (Amerindians) hosted none of the acute infectious diseases that had long bedeviled most of Eurasia and Africa: measles, smallpox, influenza, mumps, typhus, and whooping cough, among others. In most places other than isolated villages, these had become endemic childhood diseases that killed one-fourth to one-half of all children before age six. Survivors, however, carried partial, and often total, immunity to most of these infections with the notable exception of influenza. Falciparum malaria, by far the most severe variant of that plasmodial infection, and yellow fever also crossed the Atlantic from Africa to the Americas.
The disease component of the Columbian Exchange was decidedly one-sided. However, it is likely that syphilis evolved in the Americas and spread elsewhere beginning in the 1490s. More assuredly, Native Americans hosted a form of tuberculosis, perhaps acquired from Pacific seals and sea lions. But they had no counterparts to the suite of lethal diseases they acquired from Eurasians and Africans. The paucity of exportable infections was a result of the settlement and ecological history of the Americas: The first Americans arrived about 25,000 to 15,000 years ago. The domestication of species other than dogs was yet to come. So none of the human diseases derived from, or shared with, domestic herd animals such as cattle, camels, and pigs (e.g. smallpox, influenza) yet existed anywhere in the Americas. Unlike these animals, the ducks, turkeys, alpacas, llamas, and other species domesticated by Native Americans seem to have harboured no infections that became human diseases.
With the new animals, Native Americans acquired new sources of hides, wool, and animal protein. Horses and oxen also offered a new source of traction, making plowing feasible in the Americas for the first time and improving transportation possibilities through wheeled vehicles, hitherto unused in the Americas. Donkeys, mules, and horses provided a wider variety of pack animals. Thus, the introduced animal species had some important economic consequences in the Americas and made the American hemisphere more similar to Eurasia and Africa in its economy.
One introduced animal, the horse, rearranged political life even further. The Native Americans of the North American prairies, often called Plains Indians, acquired horses from Spanish New Mexico late in the 17th century. On horseback they could hunt bison (buffalo) more rewardingly, boosting food supplies until the 1870s, when bison populations dwindled. Additionally, mastery of the techniques of equestrian warfare utilized against their neighbours helped to vault groups such as the Sioux and Comanche to heights of political power previously unattained by any Amerindians in North America.
Corn had political consequences in Africa. After harvest, it spoils more slowly than the traditional staples of African farms, such as bananas, sorghums, millets, and yams. Its longer shelf life, especially once it is ground into meal, favoured the centralization of power because it enabled rulers to store more food for longer periods of time, give it to loyal followers, and deny it to all others. Previously, without long-lasting foods, Africans found it harder to build states and harder still to project military power over large spaces. In the moist tropical forests of western and west-central Africa, where humidity worked against food hoarding, new and larger states emerged on the basis of corn agriculture in the 17th century. Some of them, including the Asante kingdom centred in modern-day Ghana, developed supply systems for feeding far-flung armies of conquest, using cornmeal, which canoes, porters, or soldiers could carry over great distances. Such logistical capacity helped Asante become an empire in the 18th century. To the east of Asante, expanding kingdoms such as Dahomey and Oyo also found corn useful in supplying armies on campaign.
