The thesis of Diamond's book is that, in the words of the author:
History followed different courses for different peoples because of differences among people's environments, not because of biological differences between peoples themselves (25).
He claims that this view is largely eschewed by most academics. Historians in particular think it diminishes the importance of human action, and argue, according to Diamond, that it is deterministic. In other words, some say that Diamond's view seems to suggest that a people's environment determines everything else about their development, from their culture to the technology they develop. Diamond aspires to write what he calls a "unified synthesis" of a range of disciplines, including human genetics, history, archaeology, evolutionary biology, and epidemiology (26). To put it another way, he says that human history must be established as a "historical science, on a par with recognized historical sciences such as evolutionary biology, geology, and climatology" (32).
For the lay reader, one who is not familiar with modern scholarship on the development of human societies, one facet of Diamond's argument is especially important. He wants to underscore the idea that it was not the cultural, moral, or racial superiority of Europeans that enabled them to develop the technology that enabled them to conquer and influence peoples around the world. Rather, it was accidents of geography that facilitated the development of crops, and even pathogens that made it possible for them to do so. Diamond believes that historians have over-emphasized the importance of culture without considering the scientific foundations of its origins among different peoples.
Of course, Diamond's thesis is an answer to what he calls "Yali's question," which a New Guinean man by that name posed to him while he was doing fieldwork there:
Why is it that you white people developed so much cargo [i.e., material goods] and brought it to New Guinea, but we black people had so little cargo of our own (14)?
It was not because of any relative shortcomings, biological, cultural, or otherwise, that Europeans were able to develop more "cargo."