This symposium takes as its point of departure two books by massimo livi Bacci, Conquest and El Dorado in the Marshes, published in english in 2008 and 2010. livi Bacci assesses widely varying estimates of the demographic dimensions of the collapse of the native populations following their contact with europeans and elucidates the proximate causes of that catastrophe. drawing on models that combine production potential with demography, environment, and technology, Shripad tuljapurkar discusses analogous historical experiences of the populations of Polynesia and the social transformation they entailed. david S. Reher argues that explanations of the estimated demographic dynamics need to take into account the negative fertility responses of the indigenous population to the disruption of their traditional way of life. Focusing on the biological aspects of immunity to diseases such as smallpox, andrew noymer demonstrates that infectious diseases alone could not account for the indios' population collapse. the contributions to this symposium are based on presentations at a session at the 2010 annual meeting of the Population association of america, held in dallas, texas, that examined the demographic consequences of the Spanish conquest of the caribbean region and of South america in light of the two books.