Understanding Ethnolinguistic Differences: The Roles of Geography and Trade

I study the role of trade on inter-ethnic linguistic differences in the long run. I hypothesise that the geographic environment of neighbouring ethnic groups determines their potential gains from trade, and that the frequency of inter-ethnic trade—and resulting social interactions—shape the co-evolution of language. As a test of this hypothesis, I build a georeferenced dataset to examine the border region of spatially adjacent ethnic groups, together with variation in the set of potentially cultivatable crops at the onset of the Columbian Exchange, to identify how variation in land productivity impacts linguistic differences between adjacent ethnic groups. I find that ethnic groups separated across geographic regions with high variation in land productivity are more similar in language than groups separated across more homogeneous regions. I develop a model to theoretically ground this link between land productivity variation and inter-ethnic trade, and provide empirical evidence in support of this mechanism, including direct evidence of a causal link between land productivity variation and an ethnic group’s reliance on trade for food and subsistence in pre-modern times.