In chapter 10 of Jared Diamond's Guns, Germs, and Steel, what was the importance of diffusion?

In Chapter 10, Diamond explains that the diffusion, or spread, of crops happened more easily in some geographic locations than others. If crops are not spread naturally from one region to another, the crop must be domesticated independently in different regions, making the process more difficult.

Food production spread through natural processes in Southwest Asia (the Fertile Crescent) but not in the Americas and probably not in sub-Saharan Africa. Diffusion occurred more easily in Eurasia because of its east-west axis, meaning that areas within this region are in the same climate and biome zones. Crops that spread from the Fertile Crescent to other parts of Eurasia were therefore well adapted to the regions into which they spread, unlike in the Americas and Africa (which are on north-south axes). The orientation of a continent or region not only affected the diffusion of crops but also the likelihood that innovations would be easily spread from one part of the region to another. Regions with east-west axes, like Southwest Asia, were better able to naturally diffuse crops and innovations, making them more productive and prosperous.