Julie DeNeen was raised by her biological mother and a step-father who adopted her after DeNeen's birth father relinquished his legal rights. But she yearned for the father she never knew, wondering why he abandoned her.
"I had no picture and no contact with my biological father," said DeNeen, now 31 and married with three children in Clinton, Conn. "I hardly knew he existed."
At 13, DeNeen sought out and found her father, but after a few visits they grew apart. "I viewed him as a strange relative," she said "I wasn't prepared … and it was just awkward."
But in 2011, again obsessing over her family roots and wanting her children -- 8, 6 and 5 – to know their grandfather, DeNeen wrote him a letter, telling him she was sorry "I had fallen off the planet" and that she loved him and wanted him to "be a father figure in my life."
So they reconnected, but what evolved was far from a healthy father-daughter relationship – amidst her grief and longing, sexual sparks flew and it nearly destroyed her 10-year marriage and a fragile new bond with her biological father.
"I realized how similar we were … We could finish each other's sentences," she said. "It was a combination of elations. And there was the adrenaline and on top of the grief, thinking why can't you go back in time. And in that combination of grief and need and feeling that you fit with someone, you get a concoction that made things very confusing."
"I had this strange falling in love feeling, holding my Dad's hand," said DeNeen. "It wasn't like a daughter, it was like something else."
That something else was genetic sexual attraction or GSA.
Psychologists say that taboo is normally in place when family members grow up in close proximity by virtue of reverse sexual imprinting, or the Westermarck effect, which desensitizes them to later sexual attraction. Researchers hypothesize it evolved so biological relatives would not inbreed.
The phenomenon was first identified by Barbara Gonyo in the 1980s. She wrote a book, "I'm His Mother, But He's Not My Son," that recounted her personal story of reuniting and having sexual feelings for a son whom she had placed for adoption when she was 16. Gonyo fell in love -- a byproduct of delayed bonding that would normally have taken place in infancy, had they not been separated by adoption.
Gonyo, now a retired grandmother, created an online support group and DeNeen, who has a background in psychology, has taken up her work on a new website that she launched just two weeks ago, educating and intervening when others fall into the dangerous emotional trap of GSA.
When family members who are strangers finally meet as adults, the brain struggles to associate each other as family and, instead, they become "captivated" with one another, according to DeNeen.
"Parent and child go through a very complex bonding process from the beginning of life to the first six years," she said. "They go through phases and in the teen years, they separate. That whole process goes dormant until they reunite as adults. It's almost like it awakens back the recognition in that the other person is a mirror of yourself."
DeNeen said she felt like she was regressing back to childhood, falling in love and looking to her dad as a hero. "I felt a lot of need for intimacy," she said. "The lines were so blurry."
But she makes it clear that she never had sexual intercourse with her father, even though the relationship was "very inappropriate." And like others who experience GSA, she crossed physical boundaries that were "embarrassing, confusing, amazing and overwhelming,"