Incest between twins

Incest between twins or twincest is a subclass of sibling incest and includes both heterosexual and homosexual relationships. While in modern Western European culture such behaviour is considered taboo, incest between twins is a common feature in Indo-European, Asian (such as Japan and Bali) and Oceanian mythology, and there are a few societies in which the prohibition on it is limited or it is partially accepted.

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. The standard anthropological explanation of this custom is based in explications of the conflicts between descent and affinity in Balinese society. Twin incest was a common feature of Balinese mythology. As in many other mythologies, the Balinese deities frequently marry their siblings without any of the incest-related issues faced by similarly-situated human couples.

This was commonplace in Southeast Asian creation myths which prominently featured twin or sibling couples. In these stories, the brother usually wooed and wed his sister, who bore his child(ren), but on discovering that they are siblings, they are often (but not always) forced to part.

According to Tagalog mythology, Malakás ("strong") and Magandá ("beautiful"), the first humans on earth, were fraternal twins born of the same bamboo stalk.

An old Japanese myth says that if two star-crossed lovers commit dual suicide, they are reincarnated as fraternal twins.

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. There are strong parallels between the Germanic portrayals of twin incest and those of the Balinese Ramayana, and some scholars have speculated an early Indo-European link.

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