Sources: Alfred Crosby, “The Columbian Exchange: Plants, Animals, and Disease between the Old and New Worlds,” http://nationalhumanitiescenter.org/tserve/nattrans/ntecoindian/essays/columbian.htm. Bartoleme de Las Casas, Brief Account of the Devastation of the Indies (1542): http://www.swarthmore.edu/SocSci/bdorsey1/41docs/02-las.html Diamond, “Collision at Cajamarca,” in Guns, Germs, and Steel (1997). Nunn and Qian, “The Columbian Exchange: A History of Disease, Food, and Ideas,” Journal of Economic Perspectives 24, 2 (Spring 2010), 163-188.