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.