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Incest is sexual activity between family members who are forbidden to marry due to their close kinship. It constitutes a cultural taboo in most societies and is often prohibited by law. Which family members constitute those covered by the incest prohibition varies according to the culture. Generally, however, close members such as siblings or parents and children are included, while prohibitions on more distant relatives, such as cousins, vary. Whatever the extent of the prohibition, however, incest is almost universally condemned and viewed with horror.


Many reasons underlie the incest taboo: Biological explanations of the dangers of inbreeding support restrictions to avoid genetic disorders; psychological theories suggest that childhood experiences with one's immediate family, or others with whom one lives in close proximity, lead to a natural aversion to considering such people as potential mates; and anthropologists have noted that many societies have rules of endogamy or exogamy regulating marriage partners, and that these serve to maintain the identity of the group or solidify alliances with others. Violating the incest taboo, however, has repercussions beyond legal or social sanction, it breaks the structure of family relationships, causing pain and confusion for the individuals involved, and threatening the harmony and happiness of human society.

Forms of incest

Incest is defined as sexual activity between family members who would be forbidden (either legally or socially) to marry.[1] It derives from the Latin incestus or incestum, the substantive use of the the adjective incestus meaning "unchaste, impure," which itself is derived from the Latin castus meaning "chaste."

Incest constitutes a cultural taboo in most current nations and many past societies.[2] In many areas, incest is also prohibited by law. Which family members constitute those covered by the incest prohibition is determined by the society in which the persons live. Some societies consider it to include only those related by birth or those who live in the same household; other societies further include those related by adoption, marriage, or clan.[3]

The term "incest" can include sexual activity between family members of any gender and can include family members of any age. When one of the family members involved is a minor, incestuous activity has also been called "intrafamilial child sexual abuse."[4]

Parental incest


Sibling incest between children

Consensual incest between similar-age brothers and sisters is not uncommon, according to a study by Floyd Martinson, who found that 10-15 percent of college students had childhood sexual experiences with a brother or sister. However, only 5-10 percent of those included intercourse; and therefore most probably represent a form of childhood sexual curiosity and experimentation.[5]

Sexual relations between cousins and other distant relatives

In most of the Western world, while incest generally describes forbidden sexual relations within the family, the applicable definitions of family vary. Within the United States, marriage between first cousins is illegal in some states, but not in others. Sociologists have classified marriage laws in the United States into two categories: One in which the definitions of incest are taken from the Bible, which frowns upon marriage within one's lineage but less so on one's blood relatives; and one that frowns more on marriage between blood relatives (such as cousins), but less on that within one's lineage.

Many states prohibit marriages between first cousins, and anothers permit them only under special circumstances. Utah, for example, permits first cousins to marry only if both spouses are over age 65, or at least 55 with evidence of sterility; North Carolina permits first cousins to marry unless they are "double first cousins" (cousins through more than one line); Maine permits first cousins to marry only upon presentation of a certificate of genetic counseling. Other states with some, but not absolute, limits on first-cousin marriage are Arizona, Illinois, Indiana, and Wisconsin.



Incestuous unions were frowned upon and considered as nefas (against the laws of gods and man) in Roman times, and were explicitly forbidden by an imperial edict in 295 C.E., which divided the concept of incest into two categories of unequal gravity: The incestus iuris gentium, which was applied to both Romans and non-Romans in the Empire, and the incestus iuris civilis, which concerned only the Roman citizens. Therefore, for example, an Egyptian could marry an aunt, but a Roman could not. Despite the act of incest being unacceptable within the Roman Empire, Roman Emperor Caligula is rumored to have had open sexual relationships with all three of his sisters, (Julia Livilla, Drusilla, and Agrippina the Younger) and to have killed his favorite (Drusilla) when she became pregnant with his child.

Customs have changed in the United Kingdom, with incest at one time apparently being normal practice, at least in the south of the country. When Julius Caesar invaded Britain for the second time in 54 B.C.E., he noted the customs of the Britons, remarking, "Wives are shared between groups of ten or twelve men, especially between brothers and between fathers and sons; but the offspring of these unions are counted as the children of the man with whom a particular woman cohabited first."[7]

Laws regarding incest

Incestuous relations between adults, such as between an adult brother and sister, are illegal in most parts of the industrialized world. These laws are sometimes questioned on the grounds that such relations do not harm other people (provided the couple have no children) and so should not be criminalized. Proposals have been made from time to time to repeal these laws—for example, the proposal by the Australian Model Criminal Code Officer's Committee discussion paper, "Sexual Offenses against the Person," released in November 1996. This particular proposal was later withdrawn by the committee due to a large public outcry. Defenders of the proposal argue that the outcry was mostly based on the mistaken belief that the committee was intending to legalize sexual relations between parents and their minor children.



Scientific views


Inbreeding increases the frequency of homozygotes within a population. In some species, most notably bonobos, sexual activity, including that between closely related individuals, is a means of dispute resolution or greeting. Depending on the size of the population and the number of generations in which inbreeding occurs, the increase of homozygotes has positive or negative effects.






Leavitt argued that inbreeding in small populations can have long-term positive effects: "Small inbreeding populations, while initially increasing their chances for harmful homozygotic recessive pairings on a locus, will quickly eliminate such genes from their breeding pools, thus reducing their genetic loads."[8] However, other specialists have argued that these positive long-term effects of inbreeding are almost always unrealized because the short-term fitness depression is enough for selection to discourage it. In order for such a "purification" to work, the offspring of close mate pairings must be either homozygous-dominant (completely free of bad genes) or homozygous-recessive (will die before reproducing). If there are heterozygous offspring, they will be able to transmit the defective genes without themselves feeling any effects. This model does not account for multiple deleterious recessives (most people have more than one) and multi-locus gene linkages. The introduction of mutations negates the weeding out of bad genes, and evidence exists that homozygous individuals are often more at risk to pathogenic predation.

Social scientific views


Animals have been observed to inbreed only in extremely unusual circumstances: Major population bottlenecks and forced artificial selection by animal husbandry.

Evolutionary psychologists have argued that humans should possess similar psychological mechanisms. The Westermarck effect, that children who are raised together during the first five to ten years of life have inhibited sexual desire toward one another, is one strong piece of evidence in favor of this. This attraction stems from desensitization to one another's presence and is a sort of reverse imprinting. (Imprinting occurring when animals learn the qualities of an attractive mate.) In what is now a key study of the Westermarck hypothesis, anthropologist Melford E. Spiro demonstrated that inbreeding aversion between siblings is predictably linked to co-residency. In a cohort study of children raised communally (as if siblings) in the Kiryat Yedidim kibbutz in the 1950s, Spiro found practically no marriages among his subjects as adults, despite positive pressure from parents and community. The social experience of having grown up as brothers and sisters created an incest aversion, even though the children were genetically unrelated.

Further studies have supported the hypothesis that some psychological mechanisms cause children who grow up together to lack sexual attraction to one another. Spiro's study is corroborated by Fox (1962), who found similar results in Israeli kibbutzum. Lieberman found that childhood co-residency with an opposite-sex sibling (biologically related or not) was significantly correlated with moral repugnance toward third-party sibling incest.[9] It is not unusual for biological siblings who did not know each other in childhood to be attracted to each other when meeting as adults.

One of Sigmund Freud's most famous theories was the oedipus complex, which involves incestuous desires on the part of the child. In this complex, children wish for the death of their same-sex parent and wish to engage in sexual relations with their opposite sex parent (the version experienced by girls is known as the Electra complex). According to Freud, this complex arises when boys become aware of female genitalia and think of females as castrated by their father. The boy, not wishing to be castrated, comes to resent his father.

Endogamy and exogamy




Some cultures include relatives by marriage in incest prohibitions; these relationships are called affinity rather than consanguinity. In medieval Europe, standing as a godparent to a child also created a bond of affinity. More recently, the question of the legality and morality of a widower who wished to marry his deceased wife's sister was the subject of long and fierce debate in the United Kingdom in the nineteenth century, involving, among others, Matthew Boulton.

Religious views on incest

Biblical references

The Book of Leviticus in the Bible lists prohibitions against sexual relations between various pairs of family members. Father and daughter, mother and son, and other pairs are forbidden, on pain of death, to have sexual relations. It prohibits sexual relations between aunts and nephews, but not between uncles and nieces. Christians interpret it to include the latter by implication, though Jews traditionally do not.


The Qur'an mentions incest in the Surat An-Nisa, which prohibits a man from having sexual relationships with his mother, daughter, sister, paternal aunt, maternal aunt, and niece. Relations with wet nurses are also prohibited. But on the other side, Islam allows marriage with cousins and other more distant relatives. Only in case of marriage does Islam allow sexual relations between cousins and other distant relatives.

Hindu opposition

Hinduism speaks of incest in highly abhorrent terms. Hindus were greatly fearful of the negative effects of incest and, thus, practice, to date, strict rules of both endogamy and exogamy, that is, marriage in the same caste (varna) but not in the same family tree (gotra) or bloodline (Parivara).


  1. Henry A. Kelly, "Kinship, Incest, and the Dictates of Law, 14," Am. J. Juris (1969).
  2. Emile Durkheim, Incest: The Nature and Origin of the Taboo (Trans., 1963).
  3. Claude Lévi-Strauss, Elementary Structures Of Kinship (Tr. 1971).
  4. Ruby Andrew, "Child Sexual Abuse and the State," in UC Davis Law Review, vol. 39, 2006.
  5. Ethical Treatment for All Youth, Child and Adolescent Sexuality. Retrieved July 16, 2007.
  6. Naphtali Lewis, Life in Egypt under Roman Rule (Oxford, 1983). ISBN 0788505602
  7. John Lewis-Stempel, England: The Autobiography (Penguin, 2005).
  8. G.C. Leavitt, "Sociobiological explanations of incest avoidance: A critical claim of evidential claims," in American Anthropologist, 92: 971-993, 1990.
  9. Debra Lieberman, John Tooby, and Leda Cosmides, Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest, Proc. R. Soc. Lond. B (2003), 270, 819–826. Retrieved October 9, 2007.


  • Adams, Kenneth, M. Silently Seduced: When Parents Make Their Children Their Partners, Understanding Covert Incest. HCI, 1991. ISBN 1558741313
  • Bixler, Ray H. "Comment on the Incidence and Purpose of Royal Sibling Incest." In American Ethnologist. 9(3) (1982): 580-582.
  • Blume, E. Sue. Secret Survivors: Uncovering Incest and its Aftereffects in Women. Ballantine, 1991. ISBN 0345369793
  • DeMilly, Walter. In My Father's Arms: A True Story of Incest. University of Wisconsin Press, 1999. ISBN 0299165108
  • Durkheim, Emile. Incest: The Nature and Origin of the Taboo. Lyle Stuart, 1963. ASIN B000IXT8R0
  • Forward, Susan. Toxic Parents: Overcoming Their Hurtful Legacy and Reclaiming Your Life. Bantam, 1990. ISBN 0-553-28434-7
  • Herman, Judith. Father-Daughter Incest. Harvard University Press, 1982. ISBN 0674002709
  • Goody, Jack. "A Comparative Approach to Incest and Adultery." The British Journal of Sociology, 7(4) (1956): 286-305. Retrieved November 4, 2007.
  • Leavitt, G.C. "Sociobiological explanations of incest avoidance: A critical claim of evidential claims." In American Anthropologist. 92(1990): 971-993.
  • Lévi-Strauss, Claude. Elementary Structures Of Kinship. Beacon Press, 1971. ISBN 978-0807046692
  • Lewis, Naphtali. Life in Egypt under Roman Rule. Oxford, 1983. ISBN 0788505602
  • Lewis-Stempel, John. England: The Autobiography. Penguin, 2005. ISBN 978-0141019956
  • Lobdell, William. "Missionary's Dark Legacy." In Los Angeles Times, 2005, A1.
  • Love, Pat. Emotional Incest Syndrome: What to Do When a Parent's Love Rules Your Life. Bantam, 1991. ISBN 055335275X
  • Méndez-Negrete, Josie. Las hijas de Juan: Daughters Betrayed. Duke University Press, 2006. ISBN 978-0822338963
  • Miletski, Hani. Mother-Son Incest: The Unthinkable Broken Taboo. Safer Society 1999. ISBN 1884444318
  • Rosencrans, Bobbie and Eaun Bear. The Last Secret: Daughters Sexually Abused by Mothers. Safer Society 1997. ISBN 1884444369
  • Shaw, Brent D. Explaining Incest: Brother-Sister Marriage in Graeco-Roman Egypt. Man, New Series, 27(2) (1992): 267-299.
  • Shaw, Risa. Not Child's Play: An Anthology on Brother-Sister Incest. Lunchbox, 2000. ISBN 0970423500

External links

All links retrieved February 28, 2018.

  • Child Sexual Abuse and the State. By Ruby Andrew. UC Davis Law Review. Vol. 39, 2006. Discusses U.S. incest laws in cases where victim is a minor.
  • The Gentle People. By Nadya Labi. Legal Affairs. Jan. 2005. Intrafamilial child sexual abuse in Amish community.



