Diamond has used many kinds of research in his conclusions. We will look at the two most important types.
He has used scientific research a great deal. This comes in his chapters about diseases and plants and animals. He uses scientific research to explain why some places had more chances to domesticate plants and animals. He uses it when he explains how epidemic diseases arise in human societies.
He has also used historical, anecdotal research. This can be seen most clearly in places like Chapter 2 and Chapter 14. In Chapter 2, he uses things like historical data about Polynesian societies to hypothesize that environments cause societies to become different from one another. In Chapter 14, he uses anecdotal research from many societies to discuss the different stages of social development.