half of Nogales is so much richer than its twin just to the south of the fence, even though both were part of the same civilization five hundred years ago.
The story of Nogales highlights another major problem in adapting Diamond’s thesis: as we have already seen, whatever the drawbacks of the Inca and Aztec empires were in 1532, Peru and Mexico were undoubtedly more prosperous than those parts of the Americas that went on to become the United States and Canada. North America became more prosperous precisely because it enthusiastically adopted the technologies and advances of the Industrial Revolution. The population became educated and railways spread out across the Great Plains in stark contrast to what happened in South America. This cannot be explained by pointing to differential geographic endowments of North and South America, which, if anything, favored South America.
Inequality in the modern world largely results from the uneven dissemination and adoption of technologies, and Diamond’s thesis does include important arguments about this. For instance, he argues, following the historian William McNeill, that the east–west orientation of Eurasia enabled crops, animals, and innovations to spread from the Fertile Crescent into Western Europe, while the north–south orientation of the Americas accounts for why writing systems, which were created in Mexico, did not spread to the Andes or North America. Yet the orientation of continents cannot provide an explanation for today’s world inequality. Consider Africa. Though the Sahara Desert did present a significant barrier to the movement of goods and ideas from the north to sub-Saharan Africa, this was not insurmountable. The Portuguese, and then other Europeans, sailed around the coast and eliminated differences in knowledge at a time when gaps in incomes were very small compared with what they are today. Since then, Africa has not caught up with Europe; on the contrary, there is now a much larger income gap between most African and European countries.
It should also be clear that Diamond’s argument, which is about continental inequality, is not well equipped to explain variation within continents—an essential part of modern world inequality. For example, while the orientation of the Eurasian landmass might explain how England managed to benefit from the innovations of the Middle East without having to reinvent them, it doesn’t explain why the Industrial Revolution happened in England rather than, say, Moldova. In addition, as Diamond himself points out, China and India benefited greatly from very rich suites of animals and plants, and from the orientation of Eurasia. But most of the poor people of the world today are in those two countries.
In fact, the best way to see the scope of Diamond’s thesis is in terms of his own explanatory variables. Map 4 shows data on the distribution of Sus scrofa, the ancestor of the modern pig, and the aurochs, ancestor of the modern cow. Both species were widely distributed throughout Eurasia and even North Africa. Map 5 (this page) shows the distribution of some of the wild ancestors of modern domesticated crops, such as Oryza sativa, the ancestor of Asian cultivated rice, and the ancestors of modern wheat and barley. It demonstrates that the wild ancestor of rice was distributed widely across south and southeast Asia, while the ancestors of barley and wheat were distributed along a long arc from the Levant, reaching through Iran and into Afghanistan and the cluster of “stans” (Turkmenistan, Tajikistan, and Krgyzistan). These ancestral species are present in much of Eurasia. But their wide distribution suggests that inequality within Eurasia cannot be explained by a theory based on the incidence of the species.
The geography hypothesis is not only unhelpful for explaining the origins of prosperity throughout history, and mostly incorrect in its emphasis, but also unable to account for the lay of the land we started this chapter with. One might argue that any persistent pattern, such as the hierarchy of incomes within the Americas or the sharp and long-ranging differences between Europe and the Middle East, can be explained by unchanging geography. But this is not so. We have already seen that the patterns within the Americas are highly unlikely to have been driven by geographical factors. Before 1492 it was the civilizations in the central valley of Mexico, Central America, and the Andes that had superior technology and living standards to North America or places such as Argentina and Chile. While the geography stayed the same, the institutions imposed by European colonists created a “reversal of fortune.” Geography is also unlikely to explain the poverty of the