Natural scientists like Darwin, presented the theory of - 'Natural selection and evolution of species.

Unfortunately, this theory was misunderstood by the Nazis, and was used to gain support for genocide and racial discrimination. 
Darwin's theory stated that- " Only species, strong and intelligent enough to adapt to the changes around them are the one who survive. "

This in turn was misused as a  support for genocide which stated that only the strongest of all races shall prevail, and Nordic Aryans were thought to be the strongest race.

So, now the Nazis could also show scientific proves to reason their ideology.