poverty and of governments being unable or unwilling to undertake the public health measures necessary to eradicate them. England in the nineteenth century was also a very unhealthy place, but the government gradually invested in clean water, in the proper treatment of sewage and effluent, and, eventually, in an effective health service. Improved health and life expectancy were not the cause of England’s economic success but one of the fruits of its previous political and economic changes. The same is true for Nogales, Arizona.
The other part of the geography hypothesis is that the tropics are poor because tropical agriculture is intrinsically unproductive. Tropical soils are thin and unable to maintain nutrients, the argument goes, and emphasizes how quickly these soils are eroded by torrential rains. There certainly is some merit in this argument, but as we’ll show, the prime determinant of why agricultural productivity—agricultural output per acre—is so low in many poor countries, particularly in sub-Saharan Africa, has little to do with soil quality. Rather, it is a consequence of the ownership structure of the land and the incentives that are created for farmers by the governments and institutions under which they live. We will also show that world inequality cannot be explained by differences in agricultural productivity. The great inequality of the modern world that emerged in the nineteenth century was caused by the uneven dissemination of industrial technologies and manufacturing production. It was not caused by divergence in agricultural performance.
Another influential version of the geography hypothesis is advanced by the ecologist and evolutionary biologist Jared Diamond. He argues that the origins of intercontinental inequality at the start of the modern period, five hundred years ago, rested in different historical endowments of plant and animal species, which subsequently influenced agricultural productivity. In some places, such as the Fertile Crescent in the modern Middle East, there were a large number of species that could be domesticated by humans. Elsewhere, such as the Americas, there were not. Having many species capable of being domesticated made it very attractive for societies to make the transition from a hunter-gatherer to a farming lifestyle. As a consequence, farming developed earlier in the Fertile Crescent than in the Americas. Population density grew, allowing specialization of labor, trade, urbanization, and political development. Crucially, in places where farming dominated, technological innovation took place much more rapidly than in other parts of the world. Thus, according to Diamond, the differential availability of animal and plant species created differential intensities of farming, which led to different paths of technological change and prosperity across different continents.
Though Diamond’s thesis is a powerful approach to the puzzle on which he focuses, it cannot be extended to explain modern world inequality. For example, 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 we now need to explain why the Mexicans and Peruvians inhabiting the former lands of the Aztecs and Incas are poor. While having access to wheat, barley, and horses might have made the Spanish richer than the Incas, the gap in incomes between the two was not very large. The average income of a Spaniard was probably less than double that of a citizen of the Inca Empire. Diamond’s thesis implies that once the Incas had been exposed to all the species and resulting technologies that they had not been able to develop themselves, they ought quickly to have attained the living standards of the Spanish. Yet nothing of the sort happened. On the contrary, in the nineteenth and twentieth 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. 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. This technological gap persists today and reproduces itself on a bigger scale as new technologies, in particular those related to information technology, fuel further growth in many developed and some rapidly developing nations. Diamond’s thesis does not tell us why these crucial technologies are not diffusing and equalizing incomes across the world and does not explain why the northern