Barbara Gonyo Edvard Westermarck Freud Mackenzie Phillips Patrick and Susan Stübing Westermarck Effect

Genetic Sexual Attraction and the Westermarck Effect

The revelation by former child actress Mackenzie Phillips this week in her book High On Arrival of her 10 year long sexual affair with her father is making its rounds through the media this week. Phillips blamed the affair on serious drug use by herself and her father. By all accounts, Phillips’ father was not much involved with her when she was growing up and the affair did not occur until she was 19. While shocking, Phillip’s incestuous relationship may not be as uncommon as commonly thought.

Let’s meet Patrick and Susan Stübing a married couple with two children. By all outward appearances they are a normal family living in Germany with one important exception: Patrick and Susan are siblings. As is common among consensual adults engaged in incestuous relationships Patrick and Susan did not grow up together. As reported by the BBC, Patrick was adopted out of his birth family at a young age and did not meet his biological mother and Susan until he was 23 years old. Both Patrick and Susan report that they had an immediate attraction for one another. After their mother died they began their relationship and have been living together for the past 8 years, excluding the time Patrick has served in prison for the crime of incest. Patrick and Susan claim they are not bothering anyone and have been persecuted for their forbidden love. They have been trying to overturn Germany’s Paragraph 173 of the civil code which makes incest a crime. Medical and genetic experts claim there is a good public health reason for the law. Children produced by incestuous relationships are much more likely to have medical issues. Indeed Patrick and Susan’s son has epilepsy and learning difficulties, while their daughter is a special needs child. Nevertheless they maintain that these problems are not the result of the incestuous pairing of their genes.

The attraction that Patrick and Susan feel for each is called Genetic Sexual Attraction (GSA) and has also been reported in cases of mother-son and father-daughter incest. In all cases of GSA the relatives affected were not present during the childhood of one or both parties. The term GSA was first coined by Barbara Gonyo who founded the group Truth Seekers in Adoption – a Chicago based organization which provides support for long lost relatives who have reunited – and the website In her book I’m His Mother, He’s Not My Son, Barbara speaks frankly of the intense emotional feeling she experienced when she was reunited 26 years later with the son she gave up at age 16. Barbara describes her initial contact as a ‘honeymoon period’. She became obsessed with wanting to touch and smell her son. She is convinced that these feelings were the result of ‘missed bonding’. She recognized her son as related to her – perhaps accentuating the loss of bonding a mother experiences with her infant. These feelings may result in an intense desire for closeness which can manifest as sexual behavior in adults. In a 60 Minutes interview with some GSA couples New York psychotherapist Joe Soll characterized GSA;

“It is an attraction that develops between people who, generally speaking, have not been raised together and don’t have a taboo. They just want a hug, they want to get close and if they don’t have the taboo and they’re not careful it can turn into sex”.

The taboo Soll is speaking about is the so-called “Westermarck Effect”. Postulated by anthropologist and sociologist Dr. Edvard Westermarck,  it simply states that people raised together rarely see each other as sexual partners. It may be that the Westermarck Effect is a form of reverse imprinting where early exposure to others in the environment causes them not to be seen as future sex partners. Westermarck’s discovery is readily observable throughout human cultures and has been seen in children raised in the Israeli kibbutz system (Shepher, 1971) and marriage customs in China (Wolf & Huang, 1982). More recent research by Walter and Buyske (2003) at Rutgers University has verified the effect for females in Morocco but not males. Other research by Weisfeld et. al. (2003) and by Schneider and Hendrix (2003) supports the notion that sexual inhibition among family members has been selected for through the mechanism of natural selection and that it may be mediated by smell.

Freud was the most famous psychiatrist to write about sexual prohibition among close relatives. He claimed that unconscious lust for the opposite sex parent leads to an incest taboo (via fear of castration for males) and identification with the same sex parent. Westermarck’s theory, on the other hand, has no need for unconscious lust; the incest taboo would evolve through natural selection.

In another article Walter (1990) has speculated that since females have a greater investment in their offspring (i.e. a long pregnancy) they are more choosy than males for genetic fitness, and hence would be more likely to experience the Westermarck Effect. Certainly Walter’s later research in Morocco supports this notion. He also speculates that without the Westermarck effect older dominant males would likely exert control over younger males through control of their sexual impulses. Again this is readily observable in traditional societies around the world where adolescent rites of passage for young men involve separation from the group’s females for a period of time, not to mention proving their genetic fitness through arduous tasks. As Spain (1988) suggests, if we consider this phenomenon without the biological underpinnings it is actually similar to what Freud describes.

Unlike Mackenzie Phillips’ father, Barbara Gonyo was able to avoid a sexual encounter…but mostly because her son wasn’t interested. Eventually she was able to work through her emotions and develop a healthy relationship with her son. GSA is thought to occur in up to 50% of reunions of close relatives. The advent of in-vitro fertilization where the one or both parents do not contribute DNA to their children, could lead to a future epidemic of GSA. At the very least this is something to be aware of in the future.

– Kevin


Gonyo, B. (downloaded 2009). I’m his mother, he’s not my son. (Self-Published).

Phillips, M. (2009). High On Arrival New York, NY: Simon Spotlight Entertainment.

Schneider, M.A. & Hendrix, L. (2000). Olfactory sexual inhibition and the westermarck effect. Human Nature, 11(1), 65-91.

Shepher,  J. (1971). Mate selection among second generation kibbutz adolescents and adults: Incest avoidance and negative imprinting. Archives of Sexual Behavior, 1(4) 1573-2800.

Spain, D. H. (1988). Incest theory: Are there three aversions? The Journal of Psychohistory, 15(3), 235-253.

Walter, A. (1990). Putting Freud and Westermarck in Their Places: A Critique of Spain. Ethos, 18(4), 439-446.  

Walter, A., & Buyske, S. (2003). The Westermarck Effect and early childhood co-socialization. British Journal of Developmental Psychology, 21, 353-365.

Weisfeld, G.E., Czilli, T., Phillips, K.A., Gall, J.A., & Lichtman, C.A. (2003). Possible olfaction-based mechanisms in human kin recognition and inbreeding avoidance. Journal of Experimental Child Psychology, 85(3), 279-295.

Wolf, A.P. & Huang C. (1982). Marriage and Adoption in China, 1845-1945. The China Quarterly, 90, 310-313.