Domesticable animals are all alike; every undomesticable animal is undomesticable in its own way.

Many qualities must be present in an animal species before people can domesticate it. If any problem exists, domestication will almost certainly fail. This explains why many animals, like zebras, have never been domesticated.

People domesticated fourteen large mammals before 1900 CE. Diamond calls these animals the Ancient Fourteen, and he considers them the most important domestic animals because many of them pulled plows, provided transport, gave milk, and so on. Various small animals, including mammals, birds, and even insects, were domesticated by ancient people as well. These animals provided their owners with many advantages but not as many as the Ancient Fourteen did.

Diamond defines large animals as those that weigh more than 100 pounds. He makes a distinction between domesticated animals, which are bred and raised in captivity, and tame animals, which have not evolved to live well in captivity. Of the Ancient Fourteen domesticated mammals, only five have gained importance worldwide: cows, goats, horses, pigs, and sheep. The other nine remain important only in relatively small areas.

None of the Ancient Fourteen come from North America, Australia, or Sub-Saharan Africa. One comes from South America, and thirteen come from Eurasia. Of those, seven occurred in Southwestern Asia, in or near the Fertile Crescent. Diamond thinks this is because more large mammal species occur in Eurasia than on any other continent.

However, the prevalence of large mammals does not fully explain the fact that Eurasian mammals were more readily domesticated than were animals elsewhere. Africa and the Americas contain animals that are similar to and often related to the sheep, pigs, and cattle that Eurasians domesticated. However, most have never been successfully domesticated even by modern scientists. All of the Ancient Fourteen were domesticated within a period of a few thousand years—a much more rapid process than plant domestication, which continues to this day.

To be domesticable, an animal must grow quickly, breed in captivity, and have a diet manageable by human owners. It must also be gentle enough and passive enough to not be a constant threat by killing people or destroying property. Mean, nervous animals are usually too dangerous to domesticate. Finally, most domesticated mammals descend from wild cousins that live in social groups with detailed dominance hierarchies and overlapping ranges. This allows humans to take over the dominant role and train the animals’ natural tendency to tolerate other individuals. The Ancient Fourteen are virtually the only animals on Earth that fulfill these qualifications.