To find the answer to this question, simply look on the very first page of the Epilogue. There, Diamond says that he would tell Yali that the differences between various kinds of people "have been due not to innate differences" between the kinds of people. Instead, they have been due to "differences in their environments."
That is the one sentence synopsis of the book. Diamond has argued throughout the book that Europeans came to dominate the world because of accidents of geography and environment. He argues that Europeans were lucky, not innately superior. They were lucky because they inhabited a part of the world that was good for agriculture and, therefore, for having a large population that could lead to having "guns, germs, and steel."
What are some nongentic answers to Yali questions that Diamond dismisses?
Jared Diamonds argument is riddled with flawed thinking. Europeans were lucky and had good geography well endowed for agriculture? Really, why then is the breadbasket of the Roman Empire in northern Africa? I could go on with other similar examples. In a nut shell why Europeans would be 'lucky' is due to the ancient theological idea that the divine placed it there for them and thus they are the invested or elect people (chosen). Environment plays a role but this is really from a Biological point of view. We find environment played a strong role in Central Asia, Africa, and the Middle East, but go to Ionia and you'll find it was not the 'lucky' of that environment but rather the lacking of it that drove the innovation.