What is the author's conclusion in Chapter 4 of Guns, Germs, and Steel?

The title of this chapter is “Farmer Power.”  This tells you the general conclusion that Diamond makes in this chapter.  His conclusion is that agriculture (which he sometimes calls “food production”) allows societies to become more powerful than societies that remain as hunter-gatherers. 

The basic idea of this chapter can be found in Figure 4.1.  It shows the ultimate causes behind European dominance.  In Chapter 3, Diamond described all the reasons (which he boils down to the phrase “guns, germs, and steel) that the Spanish were able to defeat the Incas.  In Chapter 4, he briefly lays out his argument as to why the Spanish had “guns, germs, and steel” while the Inca did not.  His argument is that the people in Eurasia had agriculture before anyone else and, therefore, they became more powerful.

At the end of the chapter, he essentially sums up the message of the chapter.  He says

Hence, the availability of domestic plants and animals ultimately explains why empires, literacy, and steel weapons developed earliest in Eurasia and later, or not at all, on other continents.

What research insights do the first chapters of "Guns, Germs, and Steel" provide?

One of the major things that Jared Diamond describes regarding his research is the need to have controls, situations that help to bring out the differences in other situations.  In this case, he uses the islands of Polynesia as examples to examine the different influence of geography and other environmental factors on the advance of different societies.  Because they are islands and their socieites grew and developed almost completely independently, they help to serve as backdrops for describing the way other societies developed even though those others have more variables because they were often influenced by other societies.

A second idea that comes forward in the first several chapters is the breadth of knowledge required to make any kind of scientific inquiry relevant and meaningful when addressing something as massive in scale as the development of societies and trying to ask or examine questions about how they were different and how they developed the way they did.  The knowledge of history, geography, archeology, physical sciences, meteorology, geology, etc., that all comes into play in the discussion serves to highlight the immense wealth of knowledge one needs to effectively address this type of research.