Jared Diamond thinks that people in different parts of the world can and have evolved in different directions, depending on local selective pressures. He thinks that people in Eurasia and Africa evolved resistance to various crowd and tropical diseases, and that people that were not exposed to those infectious diseases – such as Amerindians and Polynesians – were very vulnerable to them. He thinks that that vulnerability played a part in European conquest of the Americas. All of which is correct: we know some of the genetic basis of those differences in susceptibility. I doubt if if he would argue against recent work that shows regional adaptation to cold and high altitude.
He also thinks that regionally different selective forces could and probably have caused average differences in intelligence of different groups. He does not think that everybody must be the same – does not think that evolution stops at the neck.
However, he believes that there is some principle that ensures that the intelligence differences created by those regionally varying selective pressures are the opposite of what current measurements show.