Guns, Germs, and Steel | Study Guide

Jared Diamond

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Guns, Germs, and Steel | Part 2, Chapter 9 : The Rise and Spread of Food Production (Zebras, Unhappy Marriages, and the Anna Karenina Principle) | Summary



Chapter 9 does for mammals what the previous chapter did for crops. Diamond's central question focuses on why only certain populations, and not others, domesticated large animals. He finds that an animal has to meet many criteria in order to be able to be domesticated. If even one of these is missing, the species is too difficult to domesticate. He calls this idea the Anna Karenina principle, taken from Tolstoy's novel, which states: "happy families are all alike; every unhappy family is unhappy in its own way." Diamond finds only 14 big species were domesticated before the 20th century. Of these 14, only five were major species, meaning they "became widespread and important around the world": the cow, sheep, goat, horse and pig. Most importantly, all five were to be found in the Eurasian continent. South America, for example, only had one large domesticated mammal, the ancestor that gave rise to the llama and the alpaca. In places such as Australia, the leading candidates for domestication were likely hunted out of existence.

Diamond argues cultural factors did not prevent animal domestication. To the contrary, once introduced to the concept, most peoples of the world have readily adopted the use of cows, horses, and pigs into their practices. Additionally, most peoples have developed pets, either by taming captive wild animals or domesticating and breeding smaller ones. Since roughly 4,500 years ago no major large mammal has been successfully domesticated, indicating prehistoric peoples likely exhausted the planet's available species for domestication. Efforts to domesticate moose, elk, and other species in the 20th century have all failed, for example.

Therefore, Diamond identifies six factors necessary for a large animal species to be domesticated. First, an animal's diet has to be sustainable. Most animals consume far more plant matter than what they produce in usable meat. Animals must therefore have lower ratios; carnivores are not efficient to domesticate for this reason, and very few species meet this standard. Second, animals must grow quickly. Gorillas and elephants grow too slowly to be productive in this way. Third, many species, such as the cheetah, will not breed in captivity. They have elaborate breeding rituals that preclude the possibility of domestication. Disposition is the fourth factor; mammals larger than humans must be docile for the relationship to work. Animals such as the hippopotamus, grizzly bear, buffalo, and zebra are all too fierce for domestication. Fifth, if animals are too nervous, they are not suited for domestication; big animals can harm themselves or others in a panic. Finally and perhaps most importantly, to be domesticated, large animals must have an existing social structure. Herd animals and pack animals have hierarchical social structures. Domestication is facilitated when humans assume the role of leader in the animals' social organization.


Diamond's chapter on "zebras and unhappy marriages" shows us that much like wild plant domestication, animal domestication is exceedingly difficult; exactly the right circumstances have to exist for it to take place. If a single element is missing, large mammal domestication is not possible. In his words, "only a small percentage of wild mammal species ended up in happy marriages with humans." Here again, the peoples of the continent of Eurasia had a huge advantage in that all of the five major domesticated livestock species were found in Eurasia. Eurasian societies thus possessed the major factor that leads to bacteriological immunities, which is discussed later in the book. The question of how these species benefited western Eurasian peoples in particular is taken up in the next chapter.

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