And to be precise, the Nazi concept of racial superiority was not based in intelligence. Nazis believed that the superior races are those who have instinct for collective cooperation and civilization building. It was enough if the leaders were very smart.
They believed that pure blooded Indo-Europeans created civilizations which declined as they mixed with inferior races (like ancient Greeks or Romans).
They believed that the races of second rank were those who were capable of mere maintaining of already received civilization. There were fit to be subjects to the master race.
The third rank were those who were not fit for civilized life and who should have been left alone in their tribal way of life.
Then there were smart but parasitic races which should have been isolated or eliminated.
National Socialism was seeing the mankind as species to be bred like farm animals.