The Columbian Exchange for Dummies
“And then Came the Potato…” May Be Overly Simplistic
In The Columbian Exchange: Biological and Cultural Consequences of 1492 (1972), Alfred Crosby sought to reimagine how we understood the impact of Christopher Columbus. “Man is a biological entity before he is a Roman Catholic or a capitalist or anything else,” he wrote in the preface (p. xiii). Consequently, the impact of Europeans’ discovery of the Americas needed to first be understood in terms of biology: “the most important changes brought on by the Columbian voyages were biological in nature” (p. xiv). As humans carried plants, animals, and microorganisms across the Atlantic, they reunited two ecosystems that had developed apart for thousands of years. The two worlds “began on that day to become alike.” Crosby called this movement toward biological homogeneity “one of the most important aspects of the history of life on this planet” (p. 3). It was the “Columbian Exchange.”
Yet Crosby was careful to acknowledge complexity in his story. When transplanted to the Old World, New World crops could permit previously underutilized soils to be cultivated, causing “a real jump in food production and, therefore, in population.” But, he immediately added, “before we accept this statement as gospel, let us acknowledge that we are taking much for granted”:
How can we be sure that a population which simultaneously switches from wheat to maize and increases in size could not have accomplished the increase without ever having heard of maize? Perhaps the switch to maize came not because of its greater productivity but because the people in question simply liked the way it tasted. Perhaps the increase in population stemmed from a dozen or a hundred factors having nothing whatever to do with maize. (p. 168)
Causation could not, in other words, be assumed, just because there was a correlation between the adoption of the new crops and rapid population growth. Complexity and uncertainty were therefore key to Crosby’s account.
Historical economists have nevertheless tried to identify just how much the Columbian Exchange contributed to the Great Divergence in numerical terms.
Nathan Nunn and Nancy Qian provide the most notable example. In “The Potato’s Contribution to Population and Urbanization: Evidence from a Historical Experiment” (2011), they report that the potato was responsible for “approximately one-quarter of the growth in Old World population and urbanization between 1700 and 1900” (p. 593). In the article, the preferred calculations become more precise: potatoes explain 25–26 percent of the increase in population and 27–34 percent of the increase in urbanization. It was, in other words, a case of “and then came the potato...”
To tell this story, a predictably ingenious identification strategy was used. Nunn and Qian’s treatment is not where potatoes were actually cultivated and eaten after the Columbian Exchange. Rather, they take a modern estimate of how much land in each country was potentially suitable for white potatoes, interacted with a dummy for the years 1750, 1800, 1850, and 1900, and asked whether countries with more potato-suitable land saw faster population growth and urbanization after the designated date of adoption.
But the results are fragile, as I will explain.
