According to Guns, Germs, and Steel, why did human development proceed at different rates on different continents?
The question that you ask here is actually the central question of Guns, Germs, and Steel. This exact question can be found on p. 16 of the book. The brief answer is that human development proceeded at different rates on different continents because of the different amounts of geographical luck that each continent had.
In this book, Diamond is trying to reject the idea that human development went at different rates because the people of the continents are inherently different. He says that there is no difference in intelligence between the people whose societies developed and those who did not. He says that it is wrong to argue that some continents’ cultures were better suited to development than others. In other words, we cannot blame the people whose societies did not develop for the fact that they failed to develop.
Instead, Diamond says, development was a matter of geographical luck. Diamond says that development proceeded rapidly in places where agriculture began early and where it could flourish. Places that had agriculture were able to create densely populated societies that could then create the technology that allowed them to get ahead in the world. (These places also created good environments for infectious diseases to develop, thus creating the “germs” mentioned in the title.) Some places got agriculture earlier than others, Diamond says, because they were luckier. They happened to have more plants and animals that could be domesticated easily. They happened to have geography that allowed agriculture and technology to diffuse easily from one place to another. These factors, which they could not control, were the factors that allowed them to thrive where other societies did not.
Thus, Diamond argues in Guns, Germs, and Steel that human development proceeded at different paces in different places because some places had better geographic luck and were, therefore, able to develop agriculture and “civilization” more quickly than others.