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A woman who wrote a thesis which explored the "taboo" topic of sexual attraction between close relatives who meet as adults says it is "very common".
Relatives estranged from birth who enter into relationships should be treated with "compassion", Maria Haenga-Collins said.
The comments come after a father and daughter who had a sexual relationship for almost two years were sentenced at the Dunedin District Court yesterday.
Before developing the relationship, which began when the daughter was 16, the pair had little contact with each other.
Appearing for the female offender, counsel Bernadette Farnham yesterday said psychiatric and psychological reports indicated they had genetic sexual attraction (GSA), a phenomenon which sometimes occurred between family members reunited after a long separation.
Ms Haenga-Collins, who wrote a thesis on adoption which included an interview with a woman who developed a sexual relationship with her half-brother after they were separated at birth, said there needed to be an open discussion about the topic of GSA.
The phenomenon was both "very common" and "very misunderstood", Ms Haenga-Collins, who wrote the thesis as part of a first-class honours bachelor of social work degree at Massey University said.
"There needs to be more ... compassion for people in this situation," she said.
Speaking to the participant who had a relationship with her half-brother made her realise that people who experienced GSA did not have the "social conditioning", which made them feel as though they were related.
"We are talking about two people who meet as adults and have never had the normal socialisation of brother-father, mother-son, [or] father-daughter."
Ms Haenga-Collins said she hoped the latest case would "open up discussion around GSA", which could be quite traumatic for people who first met close relatives as adults.
British research had shown that more than half of reunions between an adopted adult and a member of their birth family resulted in some form of sexual attraction, which was not always acted on, she said.