In Brave New World (1932), children are created in test tubes and maternity is held to be a disgraceful remnant of the past that only subsists in reservations for "savages". Eroticism, the privilege of civilized humanity, is part of culture, whereas natural procreation reduces one to sheer animal state. In works of contemporary science fiction, viviparity is depicted as a form of animalizing parasitism. Underlying these representations is the idea that the more "evolved" a species is held to be, that is, the less it procreates and the more it is dependent upon less evolved species in order to reproduce. The demography of modern Western societies, which conceive of themselves as the height of evolution and civilization, owe in this regard to other, supposedly less-evolved cultural groups, through migration and through the adoption of foreign children. These same, "more evolved" societies are also those that are most preoccupied with the fear of over-population which they portray as a major threat for humanity as a whole. The parasitical and swarming aspects of insect reproduction make these animals favored bad-guy characters in Hollywood science fiction. The battle of culture against nature is depicted as an unending combat between humanity and insect-like extraterrestrial species that tend to parasitize human beings in order to reproduce.