Genetic sexual attraction

Genetic sexual attraction (GSA) is sexual attraction between close relatives, such as a brother and sister, who first meet as adults.

GSA can occur as a consequence of adoption, when the adopted children discover their true ancestry and seek out relatives. Although this is a rare consequence of adoptive reunions, the large number of adoptive reunions in recent years means that a significant number of people are affected. It is generally highly distressing to both parties, as this sexual attraction is contrary to their socialized sexual and moral structures, as well as to the legal structure of society.

The theory is that close relatives, due to similar genetic makeup, may be genetically predisposed toward the same interests and have highly compatible personalities. This makes relatives who meet later in life more likely to find each other attractive than would two random people.

Normally, when children are raised together in early childhood, this phenomenon is avoided by a form of reverse sexual imprinting known as the Westermarck effect, which appears to suppress sexual desire between siblings.

In popular culture

 * In the original Star Wars movies, Luke Skywalker and his sister, Princess Leia, experienced a mild form of GSA. In Star Wars Episode V: The Empire Strikes Back, they even shared a deep kiss, although Princess Leia did this mainly to make Han Solo jealous.
 * The anime series Koi Kaze tells the story of a brother and sister (ages 27 and 15, respectively) who gradually fall in love with each other when they're reunited after a ten-year separation. A similar case occurs with the anime Onegai Twins, who in this case are the same age and have previously met.
 * The manga series Angel Sanctuary revolves around the character of Setsuna Mudo, who falls deeply in love with his sister Sarah Mudo, and goes to hades to bring her soul back to the world of the living.