Prohibited sexual relations between members of a close kinship group, such as between parents and children or between brothers and sisters. The term is often expanded to include not only actual inter-course but other sexual acts as well.
While the incest taboo is nearly universal and exists in nearly all societies, notions of kinship vary greatly from culture to culture. Thus, some cultures would consider sexual relations between first cousins incest, while others would not. The same premise holds true for inter-course between a stepfather and stepdaughter. The very rare exceptions to incest, such as those found in ancient Egyptian and Incan societies, usually involve mandatory incestuous unions within royal families, which may have been motivated by economic or theocratic considerations.
In classical psychoanalytic theory, the psychosexual development of children between the ages of three and five is characterized by incestuous desires toward the parent of the opposite sex. Sigmund Freud called these desires in males the Oedipus complex, referring to the inadvertent incest between the title character and his mother in the classical Greek tragedy, Oedipus Rex. Freud asserted that young boys form a sexual attachment to their mothers, accompanied by resentment and hostility toward their fathers, whom they regard as rivals for their mother's attention. The fear of retaliation by the father, which takes the form of castration anxiety, leads the boy to renounce his forbidden desires and begin to identify with his father, thus assuming his proper gender identity together with a superego composed of his father's moral values. Freud posited roughly the same condition, in reverse, for girls, which he called the Electra complex. While largely recognizing the widespread existence of incestuous desires (which many claim is indirectly demonstrated by the very universality of the incest taboo), contemporary psychologists differ widely with respect to the developmental and other importance they attribute to these desires.
Among the various types of incest, sexual relations between brother and sister and between father and daughter are thought to occur more frequently than mother-son incest, which is believed to be rare. The phenomenon of covert incest has been noted between mother and son, however, in which the mother acts toward her son in a sexual manner without actually seducing him. Usually, other members of the family are aware of the incestuous relationship, and it will govern the psychodynamics of the entire family structure. According to contemporary reports by incest survivors, most child sexual abuse is committed by male relatives. Fathers who abuse their daughters tend to have a history of psychological problems and emotional deprivation, and will often implement an incestuous relationship with more than one daughter. In many cases, the mother is aware of the abuse and either feels powerless to stop it or colludes with the father for reasons of her own.
Contrary to popular assumptions and stereotypes, incest occurs at all levels of society, is likely to happen in middle and upper-class families as in poor families, and takes place in families that appear outwardly happy, respectable, and well adjusted. Adults who have been incest victims in childhood are prone to depression, sexual dysfunction, and abusive behavior. Incest involving an adult victim is extremely rare. Although there has been increasing public awareness of this problem in recent years, it is believed that most cases of incest remain unreported due to the stigma involved and the powerlessness of dependent children ensnared in incestuous relationships. Over the years, many (more or less speculative) theories have been advanced regarding the origin, nature, structure, function, and interpretation of the incest taboo, but none has been generally accepted as completely definitive. One practical function of the taboo is that the prohibition of incest decreases the incidence of birth defects and recessive genetic disorders.
Maisch, Herbert. Incest. New York: Stein and Day, 1972.