It is rare to see a “big idea” in social science that also lends itself to real-world analysis. A pessimistic categorization of the field might group researchers into “storytellers” and “regression runners.” Each group has a few stars who do their work very well, with many more who wish to imitate them. There is little cross-pollination between the groups, however. That is why I was excited to see a pre-print article from the Proceedings of the National Academy of Sciences where a leading empirical researcher, David Laitin, tests a theory of Jared Diamond’s.*
Diamond’s book Guns, Germs, and Steel is part of a genre that tries to explain much of world history in a few themes. Laitin describes one of those ideas in the article’s abstract:
Jared Diamond’s Guns, Germs, and Steel has provided a scientific foundation for answering basic questions, such as why Eurasians colo- nized the global South and not the other way around, and why there is so much variance in economic development across the globe. Diamond’s explanatory variables are: (i) the susceptibility of local wild plants to be developed for self-sufficient agriculture; (ii) the domesticability of large wild animals for food, transport, and agricultural production; and (iii) the relative lengths of the axes of continents with implications for the spread of human populations and technologies. This third “continental axis” thesis is the most difficult of Diamond’s several explanatory factors to test, given that the number of continents are too few for statistical analysis. This article provides a test of one observable implication of this thesis, namely that linguistic diversity should be more persistent to the degree that a geographic area is oriented more north-south than east-west. Using both modern states and artificial geographic entities as the units of analysis, the results provide significant confirmation of the relationship between geographic orientation and cultural homogenization. Beyond providing empirical support for one observable implication of the continental axis theory, these results have important implications for understanding the roots of cultural diversity, which is an important determinant of economic growth, public goods provision, local violence, and social trust.
* These categorizations, as I said, are overly pessimistic and should not be taken too seriously. Laitin has ideas and Diamond tests his theories. But they have different comparative advantages.