The term racial hygiene was used to describe an approach to eugenics in the early 20th century, which found its most extensive implementation in Nazi Germany (Nazi eugenics). It was marked by efforts to avoid miscegenation, analogous to an animal breeder seeking purebred animals. This was often motivated by the belief in the existence of a racial hierarchy and the related fear that "lower races" would "contaminate" a "higher" one. As with most eugenicists at the time, racial hygienists believed that the lack of eugenics would lead to rapid social degeneration, the decline of civilization by the spread of inferior characteristics.