In Guns, Germs, and Steel, how did Diamond answer Yali's question?
The answer to this can be found in the Prologue and then, in more detail, throughout the entire book. The entire book is Diamond's answer to Yali.
Basically, Diamond answers Yali by saying that white people have more "cargo" because they were lucky. Diamond says that geographic luck, and not any kind of superiority of race or culture, made Europeans come to dominate the world. Europeans lived in a place where agriculture could develop easily and could spread easily. This led to big civilizations in Eurasia and the Europeans benefitted from that. The presence of all these civilizations gave the Europeans the "guns, germs, and steel" that allowed them to have more wealth and power than the New Guineans and other natives of other parts of the world.