Incest Taboo: Definition & Overview

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  • 0:01 Incest Taboo Defined
  • 0:31 Inbreeding Theory
  • 1:19 Revulsion or…
  • 2:09 Social and Cultural…
  • 2:51 Lesson Summary
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Lesson Transcript
Instructor: Tara DeLecce

Tara has taught Psychology and has a master's degree in evolutionary psychology.

In America, not only is it illegal to marry one of your siblings, but many people simply have no desire to do so. While that is the most common type of incest that comes to mind, it can include marriages between parents and children. Find out why incest is illegal and why, at a psychological level, many people find incest repulsive.

Incest Taboo Defined

The term incest taboo is defined as the prohibition of sexual relations between immediate relatives, usually between parents and children, and between siblings. The prohibition usually extends to persons adopted into or marrying into any of these primary relationships, and is thus attributed to a need to limit sexual activity to a single generation within the nuclear family group. This lesson will explain why incest is so heavily frowned upon, especially in American society.

Inbreeding Theory

One of the most commonly referenced reasons for an incest taboo is the inbreeding theory. Specifically, children that result from incestuous relationships are statistically more likely to be born with genetic defects. Studies of the probability of such defects have supported this idea.

Among royal families in England, the percentage of royal heirs born with hemophilia or even identified as carriers of hemophilia significantly increased as the degree of inbreeding increased. Studies on Japanese children that have resulted from inbreeding revealed that they were more likely to suffer from infant mortality, delayed development with walking and talking, and hearing impairments. Finally, studies on inbreeding Amish populations revealed that infant mortality was statistically more likely due to heart malformations.

Revulsion or Indifference Theory

The revulsion or indifference theory states that incest is considered a taboo because many people at the psychological level find the idea of sexual relationships with close relatives repulsive. This degree of repulsion has been reported in a number of surveys and supports the proposal that this is an adaptive psychological mechanism to avoid birth defects. It is important to note, however, that this repulsion tends to extend not to just biological relatives but any person that was around consistently during a person's childhood. Similarly, biological siblings who were separated at birth and didn't meet until adulthood tend to report some degree of sexual attraction. Therefore, it is likely that the brain decides who is repulsive based on who was deeply involved in your upbringing rather than who you are biologically related to.

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