Diamond seeks to dispel the myth that humans of different geographic and racial origins have inherently varying mental capabilities. The arguments he seeks to counter are those stating that since "civilization" came to full flower in the "western" countries (white) and not in places where other races dominated, that this indicated the innate superiority of Caucasians. He provides a stunning analysis of why civilization emerged in the places in which it did. He tells us of the few areas on the planet suitable for the emergence of farming, and why such farming flourished in some areas more than in others. He talks about the importance of domesticated animals, and shows how it was possible for them to have been domesticated in some, but not all of the theoretically possible locations. He discusses the impact of germs, the immunity defense developed by more urban dwellers, and the harm those germs can cause when those urban dwellers come into contact with peoples who lack such immunities. Although "Steel" figures prominently in the title, this aspect is given the lightest treatment in the book. Diamond closes with a plea for history to be redefined as
History Science, claiming that, as with many other "historical" sciences, it holds the elements necessary to merit the "science" designation.