Genetic sexual attraction (GSA) is incest between close relatives, such as siblings or half-siblings, a parent and offspring, or first and second cousins, who first meet as adults.
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The term was coined in the US in the late 1980s by Barbara Gonyo, the founder of Truth Seekers In Adoption, a Chicago-based support group for adoptees and their new-found relatives.
Contributing factors
People tend to select mates who are like themselves, which is known as assortative mating. This holds both for physical appearances and mental traits. People commonly rank faces similar to their own as more attractive, trustworthy, etc. than average. However, Bereczkei (2004) attributes this in part to childhood imprinting on the opposite-sex parent. As for mental traits, one study found a correlation of 0.403 between husbands and wives, with husbands averaging about 2 IQ points higher. The study also reported a correlation of 0.233 for extraversion and 0.235 for inconsistency (using Eysenck's Personality Inventory). A review of many previous studies found these numbers to be quite common.
Heredity produces substantial physical and mental similarity between close relatives. Shared interests and personality traits are commonly considered desirable in a mate. The heritability of these qualities is a matter of debate but estimates are that IQ is about 80% heritable, and the big five personality factors are about 50% heritable. These data are for adults in Western countries.
For the above reasons, genetic sexual attraction is presumed to occur as a consequence of genetic relatives meeting as adults, typically as a consequence of adoption. Although this is a rare consequence of adoptive reunions, the large number of adoptive reunions in recent years means that a larger number of people are affected. If a sexual relationship is entered, it is known as incest.
GSA is rare between people raised together in early childhood due to a reverse sexual imprinting known as the Westermarck effect, which desensitizes them to later close sexual attraction. It is hypothesized that this effect evolved to prevent inbreeding.
Instances
A brother and sister couple in Germany, Patrick Stübing and Susan Karolewski, fought their country's anti-incest laws. They grew up separately, met in 2000 when he was 23 and she was 15. He moved in with his mother and sister and the couple had four children which began in January 2001, the month after their mother died. Their appeal was rejected in 2008, upholding Germany's anti-incest laws.
Kathryn Harrison published a memoir in the 1990s regarding her four-year incestuous relationship with her biological father, whom she had not seen for almost 20 years prior to beginning the relationship, titled The Kiss.
A couple in South Africa who had been together for five years had a child and discovered that they are brother and sister just before their wedding. They were raised separately and met as adults in college.
At age 18, Garry Ryan left his pregnant girlfriend and moved to the United States. The daughter, Penny Lawrence, grew up and later set out to find her missing father. When they met, they "both felt an immediate sexual attraction". They then lived together as a couple and as of April 2012 were expecting their first child together.
In August 2012, a 32-year-old father and his 18-year-old daughter were convicted of incest after they admitted to having an incestuous relationship, which began in August 2010 when the girl was 16. The incest continued until May 2012 and resulted in the couple having a daughter, who was born in 2011. The teen told the court she was in love with her father and that they had been living as 'husband and wife' after meeting each other in 2010.