In Chapter 10 of Guns, Germs, and Steel, Diamond argues that those people who dwelt in Eurasia had a second advantage. In addition to their first advantage of a larger variety of plant and animal species that were easily domesticated, Eurasia covers the largest East-West area of any continent, in contrast to the Americas and Africa which extend farther in a North-South distance.
With this East-West arrangement, there was a clear advantage:
Axis orientations affected the rate of spread of crops and livestock, and possibly also of writing, wheels, and other inventions. That basic feature of geography thereby contributed heavily to the very different experiences of Native Americans, Africans, and Eurasians in the last 500 years.
Apparently, then, this advantage of the spread of food because of similar climates led to the ease of adaptation by animals and people alike. And, wherever food production spread slowly, then the development of technology was retarded since there was less time to focus upon what Diamond symbolically calls "steel."
This natural advantage of Eurasia is, indeed, interesting and certainly cannot be denied. Yet it is not necessarily connected to the people's total advancement as a civilization as there seem to be more elements that enter into the advancement of civilizations than food production and domestication of animals. In one chapter of Guns, Germs, and Steel, Diamond remarks in an earlier chapter upon a Native American tribe in the Northwest of the United States that had great farmland, and yet they did not advance much more than those other tribes that had to be migratory because they simply did not develop their agriculture. So, there appears to be another factor that must be present along with the environmental one.
In Chapter 10, Diamond seems to be arguing that because the climate was similar in the area of Eurasia because it was East to West, similar plants would spread and grow more easily than if they were planted in the North and the South of a country. For instance, some plants cannot grow in colder climates, just as some cannot thrive in hotter areas. Therefore, people would have to grow different plants in different places, so the likelihood of a solid crop that would have a great yield would certainly be mitigated. Planting different crops would also be more time-consuming and difficult, thus reducing agricultural yield. That the Eurasian people stayed together rather than in different groups early on was common, so there was not so much individuality in crop growth. Diamond mentions these groups only at this point:
That basic feature of geography thereby contributed heavily to the very different experiences of Native Americans, Africans, and Eurasians in the last 500 years.
That's an interesting viewpoint. How do they know that it was definitely the spread of food production and not that these places all domesticated plants individually? I'm a little confused.