Incest is a statutory crime. Incest can be defined as marriage or sexual intercourse between persons who are related within a particular degree of consanguinity or affinity prohibited by law, or between persons so closely related that a marriage between them would be void. The laws against incest intend to protect the integrity of the family and the welfare of minor children. The laws aim to prevent genetic mutations which otherwise might occur in the issue of incestuous relationships.
The crime of incest can be committed in either of two ways; first by marriage between those of prohibited degrees of blood relationship, and, second, by sexual intercourse between those so related. Under the first the marriage ceremony completes the offense. Intercourse is not a necessary part of it. Under the second, the intercourse is made the crime and marriage is no part of it[i].
The Indian Major Crimes Act (18 USCS § 1153 ) provides that any Indian who commits incest is subject to the same law and penalties as other persons committing the same offense within the exclusive jurisdiction of the United States. Under the statute, the crime of incest is not defined and punished by federal law and therefore it is defined and punished in accordance with the laws of the state in which the offense was committed. Rather than defining incest on Indian lands, federal law incorporates the state-law definition of the crime[ii].
Statutes criminalizing incest are not unconstitutional as an unwarranted governmental interference in the private sexual relations of citizens. A conviction under an incest statute for conduct that was not a crime at the time such conduct occurred will be set aside as violative of constitutional guaranties against ex post facto laws.
Rape and incest have been recognized as wholly different or independent offenses[iii]. The essential element of rape is lack of consent or legal inability to consent. However, consent or lack of consent is irrelevant to a charge of incest, which is committed by sexual intercourse between parties within a statutorily specified degree of relationship.
The concept of attempt is applicable to the crime of incest, and a person may be convicted of attempted incest under statute criminalizing incest. To support a conviction for attempted aggravated incest, the state shall prove that the defendant specifically intended to engage in a prohibited act listed in the aggravated incest statute. One who asks another to engage in sexual conduct so as to commit the crime of incest with him or her can be convicted of soliciting incest under a statute providing generally that a person who, with the purpose that an offense be committed, commands, encourages, or facilitates the commission of an offense is guilty of solicitation.
[i] People v. MacDonald, 24 Cal. App. 2d 702 (Cal. App. 1938).
[ii] United States v. Carter, 410 F.3d 1017 (8th Cir. S.D. 2005).
[iii] State v. Moore, 242 Kan. 1 (Kan. 1987).