What kind of evidence did Diamond rely on in Guns, Germs and Steel?
What makes Guns, Germ, and Steel so powerful is the breadth of evidence Diamond drew upon to build his argument. Generally speaking, there are three types of evidence: anecdotal evidence, data, and expert opinion. Diamond uses a combination of all three types of evidence from a variety of disciplines to create his watershed text.
Diamond uses the individuals he meets along his journey as anecdotal evidence. An anecdote is a story that comes from one individual's experience. In the text, he has a group of tour guides. He uses their family and personal stories as anecdotal evidence.
Diamond also draws upon a wide variety of scientific evidence. He uses data gathered by archeologists and paleontologists to explore the history of human expansion. He also uses genetic evidence to explore specific relationships between groups of people. He also uses sociological evidence. Sociology studies how humans interact with each other. When Diamond is analyzing linguistic developments, facial expressions, body language, or marital patterns, he is using sociological evidence.
Finally, Diamond uses expert opinion. He uses direct quotes and paraphrases the research done by others. Sometimes, he supports their opinion. But more often, he is using them as representatives of outdated ideas that his work is arguing against.
One of the reasons that Guns, Germs and Steel by Jared Diamond has been such a successful and influential book is the way it deploys multiple types of evidence to support its central thesis.
Guns, Germs and Steel begins with a personal anecdote, telling of Diamond's interactions with Yali and how those set Diamond on the path of writing the book to investigate why Europeans possess so much more "cargo" (material wealth and advanced technology) than the natives of Papua New Guinea. His own experiences interacting with people of differing cultures add personal credibility or what rhetoricians call "argument from ethos" to the book.
Next, he uses scientific evidence, especially from biology, geology, geography, and archaeology to make arguments about the prevalence of different types of domesticable plants and animals in different regions and how local climates and geography affected the development of civilizations.
He also uses historical evidence from various texts to describe how people lived in different periods. He uses both primary sources, written in the periods he discusses, and secondary sources, including works by modern historians and anthropologists.
Over the course of the book, Diamond uses about every kind of evidence you can think of. He uses scientific evidence, linguistic evidence, and historical evidence, among others.
For example, in the early parts of the book, Diamond uses a great deal of scientific evidence. He uses things like evidence about the size of the seeds of prehistoric grasses. He uses evidence about the ways in which diseases evolve. These are very scientific types of evidence.
In other chapters, Diamond uses "softer" kinds of evidence. He uses linguistic evidence to make claims about how the Bantu came to dominate Africa and about how Austronesians spread through the Pacific. He uses historical (and geographical) evidence to talk about the ways in which different kinds of Polynesian societies evolved.
In these ways, Diamond uses many kinds of evidence over the course of this book.