What is the question that Jared Diamond is trying to answer through his research?

From an interview with Jared Diamond:

When I set out to write Guns, Germs and Steel I wasn't trying to prove anything, but I was trying to answer a question; the biggest question of history – why history unfolded differently on the different continents over the last 13 thousand years and the usual answer to this question is the answer that racists come up with; they say its because some people are superior to other people. What we found is that the answer doesn't have anything to do with people and it has everything to do with people's environments.