Sex Offenses: Consensual

Incest between consenting adults is a crime in virtually every state. In addition, incestuous marriages are void, and a crime in their own right. There are a number of different approaches to defining incest. Some prohibitions are consanguinity-based, prohibiting sexual relations or marriage between individuals who are related by blood, to a degree of relation that varies from state to state. Other states also include relations by affinity, prohibiting sexual relations between individuals related through marriage, such as a stepparent and stepchild, or an in-law relationship.

While all cultures have some form of incest taboo, its contours vary widely. In fact, some cultures routinely practice affiliations that fall within the taboo in other cultures. The pairing of first cousins gives rise to the greatest difference in approaches. In parts of the world, the pairing of first cousins accounts for between 20 and 50 percent of all marriages (Gibbons). In the United States, however, the majority of states treat first-cousin unions as a felony. However, the incest taboo at least against parent-child and sibling relations is so strong as to put in question the need for a criminal prohibition, with self-sanction an effective alternative. Several reasons for the prohibition have been offered.

The most frequently offered explanation is the risk of genetic defects in the offspring of consanguineous relationships. There are several weaknesses to this justification for criminalization. First, the majority of criminal sexual liaisons will lead to no offspring, as the majority of sexual acts do not. In some cases reproduction will be impossible for one or both of the parties to the union, as when a woman is postmenopausal or either is infertile. Second, scientists are split on the extent of the risk of genetic defects. While closely related individuals are more likely to carry a negative recessive gene, giving it an opportunity to express itself, they also may carry a positive recessive gene. In addition, the expression of negative recessive genes provides the opportunity to eliminate them. The longer they stay recessive, the more widely distributed throughout the population they become. Though there is some increased mortality in the children of close offspring, the effect is not dramatic. Third, even if there is a significant genetic threat, criminalizing sexual unions may not be the most effective remedy, given that counseling, genetic testing, and contraception are available. Finally, genetic issues cannot explain the prohibition on sexual activity between relatives by affinity.

The weaknesses of the genetic explanation for criminal laws against incest lead us to the more plausible explanations for the law. Those are of two sorts. The first relates to the reenforcement of the cultural taboo, which may promote the cohesion of the family unit by preventing sexual jealousies and competition. Reinforcement of a cultural taboo may even be reason in itself; some people may expect the criminal law to respond to conduct that is universally disparaged. The second justification is the prevention of sexual imposition within families. While children are presumed unable to consent to sexual relations, and therefore fall outside the scope of this entry, sexual imposition among adults is still possible. Most efforts to enforce incest statutes are addressed to situations of abuse of authority, as in the case of a parent or parent substitute such as a stepparent and a child just over the age of consent.