Incest
Between an adult family member, and a child. This is usually a form of child sexual abuse. It often involves a form of threat, or the adult abuses his or her position of power. The most commonly-reported form in the Western world is father-daughter incest. This form has been shown to cause one of the worst forms of childhood trauma, a trauma that often causes serious and long-term psychological damage, especially in the case of parental incest. Stepparents are more likely to abuse stepchildren than biological parents are to abuse their children, because people typically care about their own children more than they care about their stepchildren  the Cinderella effect. It is suggested that the Westermarck effect prevents a person being attracted to anyone whom he lived in the same house as during his childhood. For this reason, most people are never sexually attracted to their siblings or parents.