How does Jared Diamond address Yali's question of why whites have been more successful than local New Guineans in his book Guns, Germs, and Steel?

Diamond asserts in his book Guns, Germs and Steel that white have been more dominate over the natives because of environmental influences.  He denies any racial superiority of whites over other races, instead focuses on the non-racial impacts.  For example, the importance of farming and the development of farming in specific regions.  The climates in certain areas were more condusive to the growth of important crops - leaving areas that were not prime for farming less developmed (like New Guinea).  The dominance of white peoples developed more by happenstance (luck of climate and location) than actual differences (intelligence, strength, etc) between the people.