Jared Diamond is, by training, a scientist. He was a physiologist and then became an ecologist and ornithologist. With this background, it is not surprising that he uses a great deal of evidence from scientific disciplines in this book.
The main scientific disciplines that Diamond uses are evolutionary biology and botany. Diamond uses evolutionary biology, for example, to discuss how Europeans came to have epidemic diseases. He discusses the reasons why, evolutionarily speaking, germs that cause regular infectious diseases can exist among hunter-gatherers while germs that cause epidemic diseases cannot. This is done mainly in Chapter 11. Diamond uses botany to look at the attributes of plants that make them good for domestication. By doing so, he identifies areas of the world that had the most domesticable plants.
Traditional historical analysis does not typically use scientific evidence of this sort as much as Diamond does. Typically, historical analysis has looked more at factors that are actually affected by human beings. Historians have generally (though this is not universally true) looked for human factors that have caused various outcomes in history. Diamond, by contrast, looks to scientific disciplines more often than is commonly done.