The final outcome of these environmentally caused processes is the rise and dominance of Europe. Almost all of history after the Ice Ages happened in the temperate midlatitudes of Eurasia.
The natural environment of this large region is better for human progress than are the tropical environments of the world, and the other temperate (or midlatitude) regions -- South Africa, Australia, and midlatitude North and South America -- could not be central for human progress because they are much smaller than Eurasia and are isolated from it and from each other. The most important of these "ultimate" factors are the natural conditions that led to the rise of food production.
(Again maize, rice, and large-seeded varieties of sorghum are dismissed, along with grains that have smaller seeds but are also used in various places as staples.) Diamond concedes that very old dates have been obtained for agricultural origins in China and tropical New Guinea: respectively 75 BC, as against 8500 BC for the Fertile Crescent.
Apparently because the Chinese center does not enjoy a Mediterranean climate, and the New Guinea center is tropical, neither (he argues) would be as old as the Fertile Crescent.
More precisely: all of the important differences between human societies, all of the differences that led some societies to prosper and progress and others to fail, are due to the nature of each society's local environment and to its geographical location.
History as a whole reflects these environmental differences and forces.
This has had "enormous, sometimes tragic consequences" for human history (p. Africa and the Americas were unable to progress throughout most of history because their "axes" are north-south, not east-west.
But Diamond is not really talking about axes; mostly he is making a rather subtle argument about the climatic advantages that (in his view) midlatitude regions have over tropical regions.
More than half of Guns, Germs, and Steel is devoted to elucidating the "ultimate" causes, explaining why differing environments led to differing rates in the acquisition of agriculture, and explaining how the resulting differences largely determined the "fate" (his word) of different peoples.
The "ultimate" causes are three primordial environmental facts: the shapes of the continents, the distribution of domesticable wild plants and animals, and the geographical barriers inhibiting the diffusion of domesticates.