The origins of the Nazi version of the theory of the master race were in the 19th-century racial theories of Count Joseph Arthur De Gobineau, who argued that cultures degenerated when distinct races mixed. It was believed at this time that the peoples of Southern Europe were racially mixed with non-European Moors from across the Mediterranean Sea, while the peoples of Northern Europe and Western Europe remained pure. Proponents of the Nordic theory further argued that Nordic peoples had developed an innate toughness and determination due to the harsh, challenging climate in which they evolved.