Diamond seeks to differentiate between proximate causes and ultimate causes in Guns, Germs, and Steel. What is the difference between these two types of causes?
Diamond's careful differentiation between proximate and ultimate causes is central to the book. One of his key concerns in writing the book is to demonstrate how global inequalities have developed. Diamond is especially interested in showing that what he calls the "good institutions" explanation for the development of inequality is insufficient. In other words, while it is true that, for example, some countries have far more stable political and economic institutions than others, and that these differences contribute to inequality, ending the analysis there only reveals a superficial picture. "Why," Diamond asks, "do some countries have good institutions while other countries don't?" There are plenty of "proximate" causes, for example, the relatively earlier development of "guns, germs, and steel" in Europe that enabled its inhabitants to colonize and exploit peoples. But Diamond looks for ultimate causes, asking why these things developed in Europe before other places. The answer, he argues, is essentially a geographical accident that allowed for the earlier development of settled agriculture. This is the ultimate cause, and—this is really the key point to the book—it is not burdened by the assumptions of cultural supremacy that often undergird the explanations that emphasize institutional development. Europeans did not develop more powerful institutions because they were superior, but rather because of accidents of geography.
The difference between these two types of causes is that proximate causes lead immediately and directly to a given result while ultimate causes lead indirectly to that result. Ultimate causes do this by leading to the proximate causes. Let us look at this with reference to Diamond’s argument.
In Chapter 3, Diamond identifies a number of proximate causes that allowed the Spanish to defeat the Incas. He boils these proximate causes down to “guns, germs, and steel.” Another way to list them is shown in Figure 4.1 where Diamond lists horses, guns and steel swords, ocean-going ships, political organization and writing, and epidemic diseases as the proximate causes of European domination. Because the Europeans had these things, they could defeat the Incas.
But Diamond wants to know why the Europeans had these proximate causes and the Incas did not. This is where the search for ultimate causes comes in. Diamond will spend the entire rest of the book laying out what he sees as the ultimate causes. He will argue that geographic luck, such as the number of domesticable species in an area and the ease with which they could spread around that area, is the major ultimate cause of European domination.
We can say, then, that ultimate causes lead to proximate causes and proximate causes lead to results such as (in this book) European domination.
The main thrust of the book is Diamond attempting to create a unified theory of the ultimate causes which resulted in the difference in technological development and acquisition of territory between European countries and other civilizations. To create such a grand, overarching theory, he argues we should not look at specific (proximate) causes, such as the historical factors leading to the Industrial Revolution. Instead, we need to look farther back at more global issues or "ultimate causes" that underlie such proximate causes.
Diamond rejects two commonly held theories about ultimate causes, namely that the ultimate causes of these differences are either due to differences in intelligence or in culture. He says they are due to geographical factors including the availability of plants and animals that can readily be domesticated. One should note that some scholars argue that Diamond tends to underestimate historical and cultural factors and often overgeneralizes or cherry-picks his historical evidence.