TOEFL iBT Practice Test 13

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The 1492 voyage of Christopher Columbus initiated a sustained transfer of plants, animals, people, and diseases between the Americas and the rest of the world, a process historians now call the Columbian Exchange, with consequences arguably more transformative than the political conquests that accompanied it. American crops such as maize, potatoes, and cassava spread to Europe, Africa, and Asia, where their high caloric yield per unit of land eventually supported significant population growth; the potato alone, once accepted in regions such as Ireland and parts of northern Europe, is credited by some historians with substantially increasing agricultural productivity in areas with poor soil unsuited to traditional grain crops. In the opposite direction, wheat, sugarcane, and horses, none native to the Americas, transformed American agriculture and warfare, with horses in particular reshaping the mobility and hunting practices of numerous Indigenous groups across the plains within only a few generations. Far more devastating was the unintentional transfer of disease: European pathogens such as smallpox, measles, and influenza, to which Indigenous American populations had no prior exposure and therefore little immunity, caused mortality rates in some regions estimated at over ninety percent within a century of contact, a demographic collapse so severe that it likely altered vegetation patterns and even, according to some recent research, regional carbon cycles as farmland reverted to forest. This catastrophic imbalance in disease transfer, rather than any single military or technological advantage, is now considered by many historians the decisive factor enabling European colonisation of the Americas.