The view that geographic factors such as climate, natural resources, disease burden or soil quality directly explain why some countries are poor still has many proponents. But these diehard geographic determinists notwithstanding, most people recognize that such geographic factors cannot explain world inequality today.

That being said, the dominant explanation about world inequality at the start of the early modern period (around 1500) is all about geography. This explanation, developed and popularized in Jared Diamond’s Guns, Germs and Steel, links inter-continental inequality circa 1500 to the historical distribution of domesticable animal and crop species. Where there were a lot of these the Neolithic Revolution — the transition from hunting and gathering to herding and farming — happened earlier and was more productive. In these places population density took off, and this spurred both technological progress and the emergence of complex societies.

A fascinating argument. But it is not an explanation for modern world inequality.

Diamond argues that the Spanish were able to dominate the civilizations of the Americas because of their longer history of farming and consequent superior technology. But then once the Incas, for example, were exposed to all the technologies they had not been able to create themselves, such as modern writing, guns and the heavy plow, and imported European animals and crops, their income levels ought to have started to converge to those of the Spanish. Yet nothing of the sort happened. In the 19th and 20th centuries, a much larger gap in incomes between Spain and Peru emerged. Today the average Spaniard is more than six times richer than the average Peruvian.

Of course, this gap in incomes is closely connected to the uneven dissemination of modern industrial technologies. But this has little to do either with the potential for animal and plant domestication or with intrinsic agricultural productivity differences between Spain and Peru.

While Spain, albeit with a lag, adopted the technologies of steam power, railroads, electricity, mechanization, and factory production, Peru did not, or at best did so very slowly and imperfectly. Diamond’s thesis does not tell us why these crucial technologies are not diffusing and equalizing incomes across the world.

Moreover, whatever the drawbacks of the Inca Empire in the early 16th century, it was undoubtedly more prosperous and had developed a more complex society than anywhere in North America. North America became more prosperous subsequently because it enthusiastically adopted the technologies and advances of the Industrial Revolution while Peru, like the rest of South America, did not. This cannot be explained by pointing to differential geographic endowments of North and South America. In fact, according to the logic of Diamond’s theory, which links prosperity and the presence of complex societies to geographic factors, one would have to presume that geography favored South America — but as we’ll argue in the next blog post, there are good reasons to think that even early prosperity is not about geography, so one shouldn’t even presume this.

Could the uneven dissemination and adoption of technologies underpinning modern world inequality be related to the factors emphasized by Diamond? For example, Diamond suggests 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.

Another fascinating argument. But again not much of an explanation for modern 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.

Another major problem for Diamond’s argument is that it has little to say about inequality within continents, which is an essential part of modern world inequality. For example, 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. But it doesn’t explain why the Industrial Revolution happened in England rather than in Eastern Europe or in the Ottoman Empire.

More critically, as Diamond himself also recognizes, 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 — the distribution of domesticable plants and animals.

The next map shows the distribution of sus scrofa, the ancestor of the modern pig, and the Auroch, ancestor to the modern cow. Both species were widely distributed throughout Eurasia and even North Africa.

The second map below 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 shows 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).

Though all of these ancestral species are present in Eurasia, their wide distribution suggests that inequality within Eurasia cannot be explained by a theory based on the incidence of these species. In fact, this wide distribution also suggests that any theory that explains the transition to agriculture purely on the basis of geographic factors — as Diamond’s theory as well as the conventional wisdom on this topic do — is at best incomplete.

We’ll see in the next blog post that there are good reasons to think that this conventional wisdom may be more than incomplete. In fact, it may have the cart before the horse.