What kind of evidence did Diamond rely on in Guns, Germs and Steel?

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.