Twin incest is a prominent feature in ancient Germanic mythology, and its modern manifestations, such as the relationship between Siegmund and Sieglinde in Richard Wagner's Die Walküre, and a feature in some Greek mythology, such as the story of Byblis and Kaunos. In these stories, the brother usually wooed and wed his sister, who bore his child or children, but on discovering that they are siblings, they are often (but not always) forced to part. Incest was commonplace in Southeast Asian creation myths which prominently featured twin or sibling couples. The standard anthropological explanation of this custom is based in explications of the conflicts between descent and affinity in Balinese society.
In traditional Balinese culture, it was common for a set of twins of the opposite sex to marry each other, since it was assumed that they had had sex in utero. Incest between twins or ' twincest' is a subclass of sibling incest and includes both heterosexual and homosexual relationships.
For other uses, see Twincest (disambiguation).
