Are there more same-sex SS than opposite-sex OS pairs among dizygotic twins? However, recent research on the sex-specific nature of breastmilk suggests that OS twins might be at a developmental disadvantage relative to SS twins. There may therefore be evolutionary selection for the tendency to have SS twins and against the tendency to have OS twins. We performed a one-sample t -test of the proportion of SS dizygotic twins against the theoretical null value of 0.
Sexual Arousal Patterns of Identical Twins with Discordant Sexual Orientations | Scientific Reports
Incest between twins or twincest is a subclass of sibling incest and includes both heterosexual and homosexual relationships. Sexual arousal from a twin sister or sister in general is referred to as sororilagnia or sorophilia , while a male analogous term is fratrilagnia ,  and a more general term is sibcest. In traditional Balinese culture, [ when? The standard anthropological explanation of this custom is based in explications of the conflicts between descent and affinity in Balinese society. Incest 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 or children, but on discovering that they are siblings, they are often but not always forced to part.
Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer.
There may be more twins in the United States than you might think. You may be familiar with the most common types of twins — fraternal and identical — but several other rare subtypes exist, too. Read on for more details about twins.