Genetic sexual attraction

Experienced between mothers and sons, fathers and daughters, and between more distant blood relatives, but most common between siblings of opposite sex who bear a close resemblance. It takes the form of an overpowering, almost electrical grip of emotion, associated with an inability to keep away from the other person and an almost primordial sense of having belonged together all their lives. The attraction gives rise to a sense of underlying shame and guilt, together with a feeling of rejection that may prevent effective communication because the emotions are too threatening to share with anyone. This may be compounded by any sexual relationship resulting from the attraction.

Particularly noted in the case of adopted children who are subsequently reunited with the biological parent or sibling of the opposite sex, seemingly because the normal bonding mechanism has been disrupted.