Guns, Germs, and Steel feedback

I wondered throughout the book about the certain aspirations as to why the author wrote the book. Was it on curiosity, was it on relevance to the present time frame of Australia, or could it have been a personal reason? This philosopher, this historian does not reveal his inspirations to this books creation. His credibility to the books creation is far fetched, that gives me the utmost confusion to the reason behind the book.