illustrated profile of a man spitting in the same direction that a pistol and three steel bars are pointing

Guns, Germs, and Steel

by Jared Diamond

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Chapter 10 Summary

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Diamond proposes that Eurasia has yet another advantage, in addition to its larger variety of domesticable plant and animal species: its geographic size and orientation. Eurasia covers the largest east–west area of any continent, whereas the Americas and Africa span greater north–south distances. Diamond hypothesizes that this orientation gave Eurasia another advantage over the other continents.

The Fertile Crescent’s package of plants and animals spread quickly and, in many cases, completely into Europe and North Africa. Most of this area had adopted a substantial number of the Fertile Crescent’s plants, animals, and food production techniques within just a few thousand years of the dawn of agriculture. Other Fertile Crescent technological innovations, such as wheels and written language, spread similarly quickly. Although the wild relatives of the Fertile Crescent’s crops lived in much of Europe and North Africa, the crops were almost never domesticated a second time. Genetic analysis shows that people throughout the region were using the crops domesticated in the Fertile Crescent, not the plants that grew naturally in their own environments. In fact, several wild beans and barleys that could have been domesticated in Europe never were—although the same species were domesticated independently in the Americas and in China. All this suggests that people throughout the region were easily able to adopt the Fertile Crescent’s entire food production package without being forced to reinvent any of it themselves.

Diamond believes that food production spread easily in Eurasia largely because the continent is arranged on an east–west axis, so the climates share similar latitudes. Neighboring areas had similar climates, day lengths, plant diseases, and so on, so the Fertile Crescent’s plants were already genetically programmed to do well in local conditions. Animals, too, adapt well to neighboring climates to the East and West of their original locations.

Food production similarly spread quickly and easily east to west from south China through the Philippines, Indonesia, and New Guinea. Africa’s Sahel zone may provide a third example of such an east–west spread of agriculture, but paleobotanists are not yet sure of the details.

Around the world, a north–south spread of food production tended to happen much more slowly. In Africa, the food production packages that did well in one area stopped spreading whenever they hit new climate zones. Ethiopian crops, which would have grown well in the climate of South Africa’s Cape, never crossed the tropics. Meanwhile, the tropical crops grown in Central Africa could not grow in South Africa’s Mediterranean climate. Farm animals spread farther than crops did, but they spread far more slowly than in Eurasia. At the limits of each climate range, the spread of herding culture stopped for thousands of years while herders slowly developed breeds that could survive in the next range to the south.

America’s north–south axis created similar difficulties. Hot, lowland climates prevented the spread of Andes crops and mammals into the Mexican highlands. Tropical climates prevented the spread of Mexican and eastern United States crops into the Andes. Crops such as corn, which did spread, did so slowly because they needed mutations to make them adaptable to varying climates. In some cases, people repeatedly domesticated related species of beans, amaranth, and other crops because they could not grow the varieties their neighbors used to the North or South. Topographical barriers such as deserts also slowed crop spread.

Wherever food production spread slowly, technology spread slowly as well. Because of this, innovations that arose in Africa or the Americas had poorer chances of reaching neighboring regions than did similar innovations in Eurasia. Thus the geographical orientation of the continents had a significant effect on the level of technological advancement they achieved.

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