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The Columbian Exchange by Alfred CrosbyProfessor Emeritus, University of Texas at Austin Millions of years ago, continental drift carried the Old World and New Worlds apart, splitting North and South America from Eurasia and Africa. That separation lasted so long that it fostered divergent evolution; for instance, the development of rattlesnakes on one side of the Atlantic and vipers on the other. After 1492, human voyagers in part reversed this tendency. Their artificial re-establishment of connections through the commingling of Old and New World plants, animals, and bacteria, commonly known as the Columbian Exchange, is one of the more spectacular and significant ecological events of the past millennium. When Europeans first touched the shores of the Americas, Old World crops such as wheat, barley, rice, and turnips had not traveled west across the Atlantic, and New World crops such as maize, white potatoes, sweet potatoes, and manioc had not traveled east to Europe. In the Americas, there were no horses, cattle, sheep, or goats, all animals of Old World origin. Except for the llama, alpaca, dog, a few fowl, and guinea pig, the New World had no equivalents to the domesticated animals associated with the Old World, nor did it have the pathogens associated with the Old World’s dense populations of humans and such associated creatures as chickens, cattle, black rats, and Aedes egyptimosquitoes. Among these germs were those that carried smallpox, measles, chickenpox, influenza, malaria, and yellow fever. The Columbian exchange of crops affected both the Old World and the New. Amerindian crops that have crossed oceans – for example, maize to China and the white potato to Ireland - have been stimulants to population growth in the Old World. The latter’s crops and livestock have had much the same effect in the Americas – for example, wheat in Kansas and the Pampa, and beef cattle in Texas and Brazil. The full story of the exchange is many volumes long, so for the sake of brevity and clarity let us focus on a specific region, the eastern third of the United States of America.