In formulating their ideology of race, Hitler and the Nazis drew upon the ideas of the German social Darwinists of the late 19th century. Like the social Darwinists before them, the Nazis believed that human beings could be classified collectively as races, with each race bearing distinctive characteristics that had been passed on genetically since the first appearance of humans in prehistoric times. These inherited characteristics related not only to outward appearance and physical structure, but also shaped internal mental life, ways of thinking, creative and organizational abilities, intelligence, taste and appreciation of culture, physical strength, and military prowess.
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To define a race, the social Darwinists affixed stereotypes, both positive and negative, of ethnic group appearance, behavior, and culture as allegedly unchangeable and rooted in biological inheritance, immutable throughout time and immune to changes in environment, intellectual development, or socialization. For the Nazis, assimilation of a member of one race into another culture or ethnic group was impossible because the original inherited traits could not change: they could only degenerate through so-called race-mixing.
The Nazis defined Jews as a race. Regarding the Jewish religion as irrelevant, the Nazis attributed a wide variety of negative stereotypes about Jews and Jewish behavior to an unchanging biologically determined heritage that drove the Jewish race, like other races, to struggle to survive by expansion at the expense of other races.