Hitler, following Häckel, believed that there were biological differences between superior and inferior races, and that the differences were scientifically based. Here is his argument drawn from Mein Kampf and from his speeches at the Nuremberg rallies.

This illustrates an important point and the political agenda take on Darwinism. Namely, the confusion/difference between EVOLUTION and SELECTION.

Recall, that we have characterized evolution as a largely random occurrence operating over a long time scale. Selection suggests pre-determination and the Nazi's run with this.

http://klio.uoregon.edu/sci/meinkampf-socialdarwin.htm