 Although Martin often writes fantasy or horror, a number of his earlier works are science fiction tales occurring in a loosely defined future history, known informally as "The Thousand Worlds" or "The Manrealm".In 2017, Martin recalled that he had started writing science fiction-horror hybrids in the late 1970s to disprove a statement from a critic claiming that science fiction and horror were opposites and therefore incompatible.Martin considered "Sandkings" (1979) the best known of these.