Jared Diamond, 1999. Guns, Germs, and Steel: The Fates of Human Societies (New York: W.W. Norton) Summary/digest by John Mackenzie.

Why is it that Europeans conquered the Americas, most of Africa, Australia, etc.? Why didn’t the Incas of Peru, or the Aztecs of Mexico, or the Ashanti of Ghana conquer Europe instead? Diamond identifies various accumulated advantages of 16th century European society that enabled Pizarro’s small band of conquistadors to conquer the entire Incan empire.

The “proximate” advantages Pizarro enjoyed over the Incan emperor Atahualpa were:

  • better resistance to epidemic diseases of Eurasian origin.
  • domesticated horses
  • superior technologies including ocean-going ships, steel and guns
  • more efficient political organization supported by writing
The conquest of the Americas was more epidemiologic than military. The primary killer was smallpox, which reached Mexico in 1620. Successive epidemics of various diseases over the next decades reduced the indigenous population from maybe 20 million to about 1.6 million. (Smallpox preceded Pizarro in Peru and had killed the previous emperor; Atahualpa was vulnerable because his claim to the throne was in dispute.) Other European diseases took similar tolls: measles, influenza and typhus were the next biggest killers, followed by diphtheria, malaria, mumps, pertussis, plague, tuberculosis and yellow fever. In aggregate, epidemic diseases reduced the native populations of the Americas by about 95 percent. The only disease of American origin that Columbus apparently brought back to Europe was syphilis.

European populations had long experience with these diseases, and had well-established resistances to them, because they had 10,000+ years of agriculture (originating in the Fertile Crescent, northern India and China) that supported concentrated human populations where epidemic after epidemic had run their courses, leaving resistant survivors. Most of these pathogens are apparently trans-species, originating in domesticated animals. Eurasians had been domesticating animals for millennia in part because the Eurasian land mass provided a relatively large number of domesticatable animal species—dog, sheep, goat, pig, cow, horse, donkey, water buffalo, camel, elephant, etc.—so animal agriculture was well developed. The Eurasian land mass and climate also offered dozens of domesticatable edible plants—the cereal and grass-derived crops wheat, rice, barley, sorghum, millet; the pulses (legumes) soybeans, peas, lentils, chickpeas, and other beans; a few tubers and melons. The well-established agrarian societies could then develop additional food sources as various tree fruits--olive, date, fig, etc.—and domesticated birds—chickens, ducks, etc.

In contrast, the Americas had very few domesticatable animals—just the dog and llama—so animal agriculture was very limited. Likewise, the Americas lacked the critical mass of domesticatable plants necessary to support widespread transformation of Native American societies from hunter-gatherers to farmers. The Americas did originate the potato, sweet potato, lima bean and peanut, but the primary vegetable staple, corn, was derived from teosinte relatively recently, and lacks protein. Without intensive agriculture, most Native American populations remained mobile and dispersed.

The human migrations across the Bering land bridge from Asia that populated the Americas are comparatively recent, and the early hunter-gatherer societies of the Americas had plentiful resources, so Native Americans apparently had less time, and probably less need, to develop agriculture. The European conquest of the Americas connected two extremes of global human migration that had isolated the European and Native American populations for tens of thousands of years. Most African and aboriginal Australian agricultures remained similarly underdeveloped. Most of the indigenous societies on these land masses were hunter-gatherers when modern European contact occurred.

The ultimate cause of Eurasia’s great agricultural advantage appears to be the east-west orientation of the Eurasian land mass, which provides one enormous, more or less continuous temperate zone in which many domesticatable species could evolve and disperse. In contrast, the north-south alignment of the Americas provides for two discrete, smaller temperate zones yielding comparatively few domesticatable species. Similarly, the African land mass spans the Equator, and has minimal ecological connectivity between north and south. Functionally, north to south, Africa is three very distinct ecological zones with four human races: the Sahara/Sahel in the north with white (Arab) and Bantu populations, equatorial tropic (with population-limiting insect-borne diseases functioning as a barrier) with Bantu and Pygmy populations, and a temperate climate in the south with Khoisan and Bantu populations. Aboriginal settlement of Australia is even more recent than human settlement of the Americas; the temperate climate and fertile soils of Australia are mostly along the eastern coast.

Eurasian agriculture supported geographic concentrations of human populations and the early rise of cities with complex political structures and social organizations. This urbanization led to increased specialization of labor, yielding economic efficiencies and new technologies such as writing, ocean navigation, steel and guns—technologies that diffused easily across the Eurasian land mass. Nomadic societies do not develop technologies such as these. Pre-Columbian agriculture in the Americas did sustain a handful of large-scale urban societies for a while, and the Olmec, Maya and Aztec cultures of Mesoamerica developed writing, accurate calendars based on sophisticated astronomy, and the zero in mathematics, but the classical city-states had mostly collapsed, with their surviving populations geographically re-dispersed, by the time the Spanish arrived.

Diamond explains why Eurasians would have these advantages, but he doesn’t explain why Europeans were the first to successfully exploit them for global conquest. Europe imported many critical technologies such as gunpowder, printing, the zero and the compass from China, India and Arabia. China had launched a huge exploration fleet in 1421, but the next emperor terminated explorations of barbarian lands.

Diamond has written elsewhere (in The Third Chimpanzee) about the enormous human cost of transition from hunter-gatherer societies to agricultural societies. A geographically dispersed hunter-gatherer population with a highly varied diet migrates to food, and can adapt to local food shortages. A geographically concentrated, sedentary agricultural society is much more vulnerable. Diets are more limited and may be nutritionally incomplete, there is greater dependence on one or two staple crops that may fail, and there is nowhere for farmers to go when their crops do fail. The geographic concentration of people with domesticated animals facilitates epidemics caused by trans-species pathogens. Diamond cites archaeological evidence that median human longevity in stable hunter-gatherer societies greatly exceeded median longevity in agrarian societies until 20th century. This suggests that agriculture may not have been a voluntary social choice, but a necessity brought about by gradual depletion of the wild plant and animal resource base upon which hunter-gatherer societies depended.