Diamond's book is excellent at synthesizing work from many fields. While his primary expertise lies in geography, Diamond also draws on work from the fields of biology, political science, anthropology, sociology, biogenetics, history, and agriculture, among others.
Take, for example, Diamond's argument in the introduction to Guns, Germs and Steel, which stems from a question posed by a New Guinea man about why Europeans were more technologically advanced than New Guineans (Diamond refers to this as "Yali's question"). Diamond's response will lead him to consider the following fields:
- Political science: Yali's question about colonialism and equality, so at heart his interests were political.
- Anthropology: Diamond reframed the question in anthropological terms, making it into a question about why societies developed differently.
- Geography: Geography plays an important role in cultural development. New Guinea's isolation from other civilizations meant that technologies developed elsewhere in the world did not spread to them.
- Archeology: Much of Diamond's recreation of the history of early peoples relies on the interpretation of archeological artifacts.
- Genetics/Physiology/Psychology: Diamond argues that cultural differences are due to environment, rather than physiological differences based on race, citing psychological research that shows that nonwhite people do not suffer from any "genetic deficiency in IQ."
- Biology: due to environmental factors, Diamond argues that certain peoples developed resistance to disease that decimated other peoples.