Guns, Germs, and Steel 4

Chapter 10 of GGS answers yet more interesting questions. This time, "Why does the spread of farming move faster on an east to west axis?" The answer lies in the question. Areas on the same line of latitude share similar qualities such as length of day and climate. Humans, as atoned to their environment as they are, have adapted similarly to their area of latitude meaning that other humans on the same east-west axis will be similar. So the answer to the question is quite simple: plants moving on an horizontal route were spreading to areas similar to that of their origins. Therefore, the species could develop and be domesticated more easily there than north of south of their original position.

Also important to the spread of crops were geographical barriers. Deserts, mountains, thick forests, and the like all played roles in preventing the spread of indigenous species. That is why the people of The Sahara domesticated camels but not Africans further south. The same can be said for the Americas, for example the domestication of llamas in Mexico but not further south or north. As we can see, the domestication of certain plant and animal species was heavily affected by both longitude and geography.