The Economics of Animal Domestication

Roughly fourteen thousand years ago, humans and wolves entered into what is probably the most consequential interspecies relationship in the history of the planet. The terms of this arrangement — dogs would provide hunting assistance, guarding, and eventually herding; humans would provide food, protection, and tolerance — were never negotiated, but they were stable enough to persist across every subsequent human civilization on every inhabited continent. The dog is the one animal that was independently domesticated on multiple continents, which tells you something about the mutual benefits of the relationship. The dog aside, however, the distribution of domesticated animals across human history is extraordinarily uneven, and that unevenness has had consequences for human economic development that reverberate into the present.

The Eurasian landmass had, at the beginning of the Holocene, a remarkable collection of large mammals that proved amenable to domestication: the wild aurochs (ancestor of cattle), the wild boar (ancestor of pigs), the mouflon (ancestor of sheep), the bezoar ibex (ancestor of goats), the wild horse, the wild ass, the Bactrian camel, and several others. Sub-Saharan Africa had vastly more large mammal species in absolute terms — the continent is still famous for its megafauna — but almost none of them proved domesticable. The Americas had a few: the llama and alpaca in South America, the turkey and the Muscovy duck. Australia had essentially none. This distribution was not a consequence of human failure or human ingenuity. It was an ecological accident, determined by the specific behavioral and physiological characteristics of the animals that happened to be present and by the prior history of human-megafauna interactions in each region.

Jared Diamond’s argument, developed most fully in Guns, Germs, and Steel, is that this distribution of domesticable animals goes a long way toward explaining the subsequent divergence in economic and military power between Eurasian civilizations and those elsewhere. The argument has several distinct strands that are worth separating analytically. The most direct strand is the economic productivity argument: pastoral societies that kept large domesticated animals had access to traction, dairy, fiber, and meat in combinations that purely agricultural or hunter-gatherer societies did not. An ox-drawn plow can cultivate perhaps ten times as much land per day as a human with a hand tool. That productivity differential compounded over millennia. Societies with traction animals produced agricultural surpluses that supported larger non-agricultural populations — artisans, soldiers, administrators, merchants — who in turn generated the institutional complexity and technological sophistication that characterized the leading civilizations of the ancient world.

The military strand of the argument is perhaps even more dramatic in its consequences. The horse was domesticated on the Eurasian steppe around 3500 BCE, and within a millennium it had transformed warfare across the entire landmass. The sequence runs from horse-drawn chariots in Mesopotamia and Egypt, to cavalry warfare in the Iron Age, to the steppe nomad empires — Scythian, Hunnic, Mongol — that periodically overwhelmed settled agricultural societies despite enormous differences in population. The Mongol conquests of the thirteenth century, which extended from Korea to Poland and destroyed some of the wealthiest urban civilizations of the medieval world, were only possible because the horse had been domesticated on the Eurasian steppe and the Mongols had millennia of accumulated knowledge about how to breed, feed, and fight from horseback. This knowledge had no analog in the Americas. When Spanish conquistadors arrived in Mexico in 1519 with a few dozen horses, the animals appeared to Aztec observers as creatures of almost supernatural capability, because nothing like them had ever existed in the Americas since the extinction of the American horse thousands of years earlier.

The epidemiological strand of Diamond’s argument is the one that has attracted the most attention and generated the most controversy, and it is also the most economically consequential in the long run. The major epidemic diseases of human history — smallpox, measles, influenza, plague — are all zoonotic diseases that originated in domesticated animals and subsequently adapted to human hosts. Smallpox originated in cattle pox or a related bovine virus. Measles derived from rinderpest. Influenza has an avian reservoir and spreads through pig populations before jumping to humans. Plague circulates in rodent populations, particularly those that live in proximity to human grain stores. The pattern is consistent: dense human populations living in close contact with large domesticated animals are repeatedly exposed to animal-borne pathogens, some fraction of which adapt to human transmission, and the survivors of these epidemics develop partial immunity.

The implication is that Eurasian populations, after ten thousand years of living with cattle, pigs, sheep, goats, and horses, carried a significant degree of inherited or acquired resistance to a suite of animal-derived pathogens that populations without these animals had never encountered. When European colonizers arrived in the Americas, Australia, and Sub-Saharan Africa, they brought with them not just weapons and political organization but a portfolio of epidemic diseases to which indigenous populations had no resistance. The demographic consequences were catastrophic and have been well documented: population decline of 50 to 90 percent in the generations following first contact is not uncommon in the historical record. These population collapses were not incidental to the European conquest of the Americas — they were the central mechanism by which small numbers of European soldiers were able to overwhelm civilizations that had previously sustained large, organized populations. Hernán Cortés conquered the Aztec empire with a few hundred soldiers not because of his military genius but because smallpox had already killed perhaps half the Aztec population by the time his forces reached Tenochtitlán.

The geographic determinism argument raises a legitimate objection that must be addressed: does it explain too much? If the distribution of domesticable animals was fixed by ecology, and if this distribution determined the subsequent trajectory of human development, then human agency is largely removed from the story. Cultures, institutions, decisions, and ideas are epiphenomenal. This is a strong claim and a disturbing one, because it implies that the massive inequalities in wealth between regions of the world today are traceable ultimately to the distribution of wild ungulates ten thousand years ago. The determinism is not total — Diamond’s argument is about initial advantages and the compounding of advantages through time, not about inevitable outcomes — but it assigns a remarkably small role to human choice in explaining the divergence of civilizations.

The economic historian’s response to this objection is to distinguish between necessary and sufficient conditions. The presence of domesticable animals in a region was necessary for pastoral economies to develop there; it was not sufficient. Many Eurasian societies had access to horses and cattle without developing them into the productive advantages that some of their neighbors achieved. The Mongols, who had horses, built an empire based on conquest and extraction rather than production. The Romans, who had cattle, built an empire based on agricultural production, trade, and urbanization. The same animal advantage was deployed very differently by different societies, reflecting genuine differences in institutions, culture, and collective choice. Geography set the menu of options available; human societies chose from that menu, and the choices mattered.

The pastoral economy also had internal dynamics that are worth examining in their own right, independent of the geographic determinism argument. Societies that kept large herds of domesticated animals developed specific institutional adaptations that distinguished them from purely agricultural societies. Property rights in mobile animals are more difficult to enforce than property rights in fixed land, because the animals move and can be stolen. Pastoral societies developed strong kinship-based institutions for defending herds against theft, complex systems of branding and marking to establish ownership, and social norms around hospitality to strangers that reflect the importance of maintaining reciprocal relationships with neighboring groups on whom you might depend during periods of drought or forage shortage. These institutional adaptations were functional responses to the specific economic problems of managing mobile wealth in open landscapes — and they produced social structures that were quite different from the village-based, territorially fixed social structures of purely agricultural societies.

The interaction between pastoral and agricultural societies, across the Eurasian landmass, generated much of the economic dynamism of the ancient and medieval world. Pastoral nomads produced animal products — meat, dairy, leather, fiber, horses — that agricultural societies wanted. Agricultural societies produced grain, craft goods, and metal that pastoral societies needed. The trade between them was extensive enough that the Silk Road was in part a conduit for pastoral-agricultural exchange, not just for luxury goods moving between China and Rome. The periodic raids and conquests that punctuated this trade relationship were not simply acts of violence; they were also redistributive mechanisms in which pastoral societies with military advantages extracted surplus from agricultural societies with productive advantages, in a predator-prey dynamic that characterized much of Eurasian history from the Bronze Age to the early modern period.

The end of the pastoral nomad as a military threat is itself an economic story. The development of firearms in the fifteenth and sixteenth centuries eroded the cavalry advantage that steppe nomads had held for two millennia. The musket and the cannon made it possible for settled agricultural societies to defeat mobile cavalry forces on the open steppe, not because settled peoples were braver or more organized but because the technology of military killing had changed in ways that disadvantaged horses. The Qing conquest of Mongol territories in the eighteenth century and the Russian expansion across the steppe in the same period were the final chapters of the pastoral-agricultural competition that had dominated Eurasian history for thousands of years. The economic geography that the domestication of the horse had created was undone by a technology that the agricultural civilizations had invented — made possible, in turn, by the surplus production and urban complexity that their own animal domestications had originally enabled. History rarely moves in straight lines, but the arc from the domestication of the aurochs to the cannon foundry is straighter than it appears.