What's the author's purpose in Chapter 13 of Guns, Germs, and Steel?

In Chapter 13 of Guns, Germs, and Steel, Jared Diamond is trying to show that the technological level that a society achieved by about 1500 or so AD was determined by geographical factors and not cultural factors.  This fits in with Diamond’s major argument in this book, which is that geographic luck determined which countries became powerful by the Age of Exploration.

Most people believe, Diamond says, that the Europeans became the most technologically advanced society in the world by 1500 AD because they were in some way superior.  Even if people do not think they were genetically superior, they believe that there was something about European culture that was better suited to gaining power in the world.  In Chapter 13, Diamond says that such people believe that European culture was more likely to accept change and was more likely to promote inventiveness than other cultures.  Such people say that Europe gained its edge in technology because its culture was more conducive to technological innovation.

Diamond’s purpose in Chapter 13 is to disprove this idea.  He says that different cultures in different regions of the world have different attitudes towards change.  For example, he discusses two tribes in New Guinea, one of which welcomes technological change and one which does not.  He argues that there are such differences in every region of the world so we cannot say that people in Eurasia were, on the whole, more likely to accept change than people in New Guinea or Australia.

So why, then, did some societies come to have more technology?  On p. 261, Diamond lays out three factors that, he says, determined this.  He lists these three factors as “time of onset of food production, barriers to diffusion, and human population size.”  He says that these are all determined by geography.  Onset of food production was determined by things like the climate in a region and the number of domesticable plant and animal species present.  Barriers to diffusion include the general shape of a landmass (if it is longer east to west or north to south) and geographical features such as mountains, deserts, and jungles.  Human population size is generally determined by how well-suited a given area was for agriculture.  All of these are determined by geography, not culture.  This means that a society’s level of technology was determined by geography and not by culture.  Diamond’s purpose in Chapter 13 of Guns, Germs, and Steel is to make this point, which bolsters his overall argument that societies that gained power and wealth did so because of their good geographic luck.