In this chart, Diamond is attempting to show us what
factors led to the Europeans' possession of "guns, germs and steel" and other "proximate
causes" of their ability to defeat people such as the
Incas.
At the bottom of the chart, we see the things that
actually allowed the Europeans to be so dominant. These are things like horses, guns,
ships, political organization, and epidemic diseases. We all know that these things
helped the Europeans, but Diamond says knowing this is not enough. Instead, he says, we
have to understand why the Europeans had these things while the Incas and others did
not. This is the purpose of this chart.
The chart shows
the factors that made these proximate causes happen. For example, we can see that
Europeans had epidemic diseases because they had many domesticated plant and animal
species. We can see that they had many domesticated species because of things like the
east-west axis of Eurasia and the consequent ease of species
spreading.
Overall, then, this chart shows us the ultimate
causes of the things (horses, guns, diseases, etc) that allowed the Europeans to
dominate the world.