This question appears to refer to Chapter 13 in Guns, Germs, and Steel. This chapter, entitled “Necessity’s Mother,” looks at why some societies seem to innovate more than others. About midway through the chapter, on p. 249, Diamond begins to set out a “laundry list” of 14 factors that, he says, have been offered as reasons why some societies are more innovative than others. However, Diamond these suggested factors. Later, at the end of the chapter, he offers four factors that, in his mind, really determine which areas of the world got technology and which did not. He differentiates between the two by saying that the laundry list is, at best, a list of proximate causes while the four factors that he identifies are ultimate causes.
Throughout this book, Diamond tries to determine the ultimate causes behind various phenomena. He does not think that it is all that helpful to know what the proximate causes are if you cannot identify the ultimate causes. That is why, for example, he is not satisfied with saying that “guns, germs, and steel” allowed Europeans to dominate the world. Instead, he wants to know why the Europeans had those things while other people did not.
After discussing all the factors on the “laundry list,” Diamond says on p. 251 that
all of these proximate explanations bypass the question of the ultimate factors behind them.
He is saying that the laundry list only includes proximate causes and that we should, instead, look for ultimate causes. At the end of the chapter, he identifies four ultimate causes. On p. 263, he says that “area, population, ease of diffusion, and onset of food production” were the factors that ultimately determined which areas became technologically advanced and which did not.
Thus, Diamond differentiates between the laundry list of proximate causes and the four more ultimate causes that led some areas of the world to innovate more than others.