Incest

Incest is defined as sexual activity between people who are closely related. Incestuous relationships can occur between people who are related through genetics (consanguinity) or those who are related by marriage (affinity). Some incest occurs in the form of rape or sexual assault of a juvenile by an adult relative.

Consanguineous incest, or the type that occurs between close blood relatives such as parent/child and brother/sister, is a nearly universal cultural taboo. It is prohibited and outlawed in most Western cultures. Offspring produced from these close relationships have a higher mortality rate than the general population. They also are at greater risk for congenital (inherited) abnormalities and other serious health disorders.

In certain cultures, including those in the Middle East and northern Africa, marriage between blood relatives is a tradition that sometimes is still followed. Additionally, at various times in history, royal dynasties have favored marriage between blood relatives in a belief that limiting procreation with outsiders kept the royal bloodline pure.

Degree of Relationship

Many countries around the globe have laws that dictate the degree of consanguinity/affinity at which people are allowed to marry. This means the law says how far removed relatives must be in order to join in a legal union. The degrees of relationship used in legal terms differ slightly from those used by geneticists, who classify first-degree relatives as those who share 50 percent of their genetic material (parents, children, and siblings).

For legal purposes, most government institutions define degrees of consanguineous relationship as follows:

• First-degree relatives: parents and children (including adopted children)
• Second-degree relatives: siblings, grandparents, and grandchildren
• Third-degree relatives: aunts, uncles, nieces, nephews, great-grandparents, and great-grandchildren
• Fourth-degree relatives: first cousins, great aunts, great uncles, great-great-grandparents, and great-great-grandchildren

Relationships of affinity also are defined by degree, as follows:

• First-degree relatives: spouse, step-parents, and step-children
• Second-degree relatives: step-siblings, parents-in-law, daughters-in-law, and sons-in-law
• Third-degree relatives: grandparents-in-law, sisters-in-law, brothers-in-law, and grandchildren-in-law
• Fourth-degree relatives: first cousins-in-law, aunts-in-law, uncles-in-law, nieces-in-law, nephews-in-law, and great-grandchildren-in-law

Degrees of relationship continue beyond this to indicate the relationship between, for example, second cousins, third cousins, and so on.

Inbreeding Problems

The sexual reproduction of offspring between closely related humans is referred to as inbreeding. Because children inherit half of their genes from each parent, inbred offspring are more likely to present with rare genetic conditions and disorders. This is due to the amount of shared genetic material between their parents, which makes it more likely for recessive genes (genes that usually do not express) to be dominant in these children.

Common congenital disabilities likely to occur in offspring of close relationships include heart conditions, cleft palate, hearing impairments, visual problems, and fluctuating asymmetry (uneven placement and size of the eyes and ears). Inbred offspring are more likely to present with rare disorders such as hemophilia, albinism, cystic fibrosis, and immune diseases. Additionally, mortality rates in the first year of life tend to be higher for these children; those who survive to adulthood tend to be of shorter stature than the general population.

Incest in History

Incest has been common in certain cultures in history, most notably in ancient Egypt in the fourth dynasty (2700–2650 BCE). Preserved artifacts indicate that many royal marriages occurred in brother/sister pairs during this time. Although no documented artifacts from this time period offer an explanation as to why this occurred, some experts believe that the practice grew from the idea that members of the royal family were divine. Since they had no peers among mortal human beings, they, like the gods, married each other.

Royal incest was common at different points in pre-history in Inca Peru, Central Africa, Mexico, Hawaii, and Thailand. It also was quite common among European royalty from the fifteenth century to as late as the nineteenth century. Many notable royal houses supported marriage between close cousins, including the Spanish Habsburgs, the Prussian Hohenzollerns, the French Bourbons, the Russian Romanovs, and various British royal families.

Experts believe that this level of inbreeding eventually led to the demise of royal families like the Spanish Habsburgs. The Habsburgs ruled Europe from about 1500 to 1700 CE. During this time, branches of the family dynasty ruled over Austria, Hungary, Belgium, the Netherlands, the German Empire, and Spain. However, centuries of inbreeding led to physical and mental problems. In fact, records show that nearly half of the babies born to the Habsburgs during this time died before their first birthday. The last ruler of the family, King Charles II, died at age thirty-nine of complex health issues in 1700 CE. Analysis of his lineage showed that so many intermarriages had occurred between first cousins and uncles and nieces that his DNA was nearly as inbred as the offspring of a relationship between a brother and sister or a father and daughter.

Experts also suggest that incest was practiced among royal families in an effort to protect royal assets and prevent them from being divided among people beyond the royal family. Interfamily marriages helped to ensure that power, wealth, and privilege remained in the hands of a select few.

Bibliography

Bittles, Alan H. "Incest." Consanguinity in Context. Cambridge UP, 2012, pp. 178–92.

Boehrer, Bruce Thomas. Monarchy and Incest in Renaissance England. U of Pennsylvania P, Inc., 2015.

Clementsson, Bonnie. Incest in Sweden, 1680-1940: A History of Forbidden Relations. Lund UP, 2020.

Davis, Shirley. "Incest and Genetic Disorders." CPTSD Foundation, 18 Apr. 2022, cptsdfoundation.org/2022/04/18/incest-and-genetic-disorders. Accessed 10 Dec. 2024.

Helmenstine, Anne M. "Inbreeding: Definition and Genetic Effects." ThoughtCo., 18 Aug. 2024, www.thoughtco.com/inbreeding-definition-effects-4171861. Accessed 10 Dec. 2024.

Sabean, David. A Delicate Choreography: Kinship Practices and Incest Discourses in the West since the Renaissance. Walter de Gruyter GmbH, 2023.

Scheidel, Walter. “Brother-Sister and Parent-Child Marriage Outside Royal Families in Ancient Egypt and Iran: A Challenge to the Sociobiological View of Incest Avoidance?” Ethology and Sociobiology, vol. 17, no. 5, pp. 319–40, doi.org/10.1016/S0162-3095(96)00074-X. Accessed 10 Dec. 2024.

Shaw, Alfie. "What Are the Effects of Inbreeding?" BBC Earth, www.bbcearth.com/news/what-are-the-effects-of-inbreeding. Accessed 10 Dec. 2024.