The world's largest continuous zone of "temperate" climates lies in a belt stretching across Eurasia from southern Europe in the west to China in the east.
Rather persistently neglecting the fact that much of this zone is inhospitable desert and high mountains, Diamond describes this east-west-trending midlatitude zone of Eurasia as the world region that possessed the very best environment for the invention and development of agriculture and, consequently, for historical dynamism.
The first and most basic cause is the shape of the continents: their "axes." A continental landmass with an "east-west axis" supposedly is more favorable for the rise of agriculture than a continent with a "north- south axis." Diamond divides the inhabited world into three continents (he uses the word "continent" rather broadly): Eurasia, Africa, and the Americas.
Eurasia has an east-west axis; the other two have north-south axes.Culture is largely irrelevant: the environment explains all of the main tendencies of history; cultural factors affect the minor details.Diamond proceeds systematically through the main phases of history in all parts of the world and tries to show, with detailed arguments, how each phase, in each major region, is explainable largely by environmental forces.(Whatever deficiencies some of these staples may have had were amply compensated for by eating more of them, along with supplementary foods.) He dismisses tropical grains.Maize, he says, is less nutritious than the main Fertile Crescent grain domesticates, wheat and barley (apparently confusing moisture content and nutritiousness), and since early domesticated varieties of maize had small cobs and kernels, it would follow (he thinks) that maize took much longer than other grains did to become fully domesticated.Although many civilizations arose and flourished in temperate Eurasia, only two were ultimately crucial, because of their especially favorable environments: China and Europe. Those world regions that became agricultural very early gained a permanent advantage in history.Finally: Some 500 years ago China's environment proved itself to be inferior to Europe's in several crucial ways. Diamond distinguishes between the "ultimate factors" that explain "the broadest patterns of history" and the "proximate factors," which are effects of the "ultimate factors" and explain short-term and local historical processes. The "ultimate" causes led, in much later times, to regional variations in technology, social organization, and health; these, then, were the "proximate" causes of modern history.The final outcome of these environmentally caused processes is the rise and dominance of Europe. Almost all of history after the Ice Ages happened in the temperate midlatitudes of Eurasia.The natural environment of this large region is better for human progress than are the tropical environments of the world, and the other temperate (or midlatitude) regions -- South Africa, Australia, and midlatitude North and South America -- could not be central for human progress because they are much smaller than Eurasia and are isolated from it and from each other. The most important of these "ultimate" factors are the natural conditions that led to the rise of food production.This has had "enormous, sometimes tragic consequences" for human history (p. Africa and the Americas were unable to progress throughout most of history because their "axes" are north-south, not east-west.But Diamond is not really talking about axes; mostly he is making a rather subtle argument about the climatic advantages that (in his view) midlatitude regions have over tropical regions.