Roger Stanyard writes:

Where on earth would [Hitler] have got creationism from?

From the Bible for a start, see Genesis 1 for God creating humans in their current form. These sort of ideas were predominant in most of Christendom for most of Christendom's history. You don't need to understand and reject evolution to be a creationist, you merely need to believe that God created humans in much their current form.

And Hitler believed exactly that. Mein Kampf sets out Hilter's belief that it was Aryans who were the created race in the Garden of Eden. His eugenics policy was aimed at preserving this Aryan ideal in its original God-created form ("God's highest handiwork"), he did not want Aryans to interbreed with what he saw as lesser races. From Mein Kampf: "Whoever would dare to raise a profane hand against [i.e. interbreed with] that highest image of God among His creatures [i.e. Aryans] would sin against the bountiful Creator of this marvel and would collaborate in the expulsion from Paradise."