Jared Diamond strongly believed that geography is fundamental to the development of civilizations. Where continents lie in relation to latitude affects in a great expense its potential for food production.
A quick look at a world map will reveal a stark difference between the geography of the Fertile Crescent as compared to Africa or America. The continents differ in axis orientation.The Fertile Crescent has an East-West axis. Its land mass is larger in width rather than length. Because of almost the whole region lies in the same latitude, the climate is the same everywhere. That is why the major crops of Fertile Crescent spread throughout the entire region.
Thus, food production as a whole prospered which is the foundation of a stable society. On contrast, Africa has a North-South axis. The crops from Fertile Crescent prospered in Egypt. However, downwards to Ethiopia which is characterized by highlands, they all failed to develop. That Ethiopia lies in lower latitude than Egypt and the climate there is not suitable for wheat or barley. In Sub-Saharan Africa, however, wild plants were domesticated because of the summer rains and warm temperature.
Yams and sorghum which are indigenous to West Africa and the Sahel zone became bountiful. Horses which also came from Fertile Crescent never thrived south of the equator. It took centuries before goats, sheep and cattle were domesticated in South Africa. This is also the case in America. Potatoes, guinea pigs and llamas were domesticated in Mexico highlands which its cold climate. They are also suitable for the southern part of the Andes because of its similarity in latitude and climate. However, these crops and animals did not spread northward to Central America with its hot lowlands. On the other hand, sunflower and turkeys from Mexico thrived north of the Andes but not southward because of the tropical climate.
Therefore, crop diffusion in Central and South America became very selective and slow.