The Potato's Contribution to Population and Urbanization: Evidence from a Historical Experiment. Nathan Nunn, 2011, Paper. "We exploit regional variation in suitability for cultivating potatoes, together with time variation arising from their introduction to the Old World from the Americas, to estimate the impact of potatoes on Old World population and urbanization. Our results show that the introduction of the potato was responsible for a significant portion of the increase in population and urbanization observed during the 18th and 19th centuries. According to our most conservative estimates, the introduction of the potato accounts for..." Link