What do you mean by incest?

Sibling love : Why incest is repulsive to most people

Patrick S. has to go to prison for his love for his sister. He violated the prohibition of incest. Just like Oedipus, the figure from the Greek legend. Without knowing it, the king's son Oedipus kills his father and marries his mother. Only later does he find out that he has committed parricide and incest and goes into exile. He's cursed.

The incest taboo, i.e. the prohibition of sexual intercourse with close relatives, is apparently as old as human culture and is widespread all over the world. For Sigmund Freud, the founder of psychoanalysis, the incest taboo was, above all, a social barrier to our inherent need to have sex with our mother or father. The result of the oppression is the Oedipus complex, Freud concluded.

But at the same time as the Viennese neurologist, the Finnish anthropologist Edvard Westermarck made another claim based on the theory of evolution. Westermarck's thesis: the incest taboo is innate. People who grow up together do not find each other sexually attractive. On the contrary, most will find the thought of having sex with a mother or sister instinctively repulsive.

This aversion to inbreeding is probably nature's emergency brake. This is because the offspring of people who are closely related are more likely to have genetically determined malformations. The explanation: Our cells contain two complete copies of the genetic material - one from the mother and one from the father. If a gene is now defective, the error can be compensated for by the second copy.

It doesn't work so well anymore when the child is from brother and sister. Then both copies of the genome are half identical, so weaving errors in the genes can no longer be compensated as well. Malformations and miscarriages are increasing, even if the 50 percent figure that is sometimes mentioned is likely to be too high.

Westermarck's theory of our inherent rejection of inbreeding has now been confirmed in humans and in many animal species, from mice to chimpanzees. Many animals have sophisticated mechanisms with which too great a genetic proximity is recognized and avoided during reproduction. Mice, for example, spray a kind of genetic calling card with their urine that repels closely related conspecifics - you can't smell yourself.

But that's only one side of the coin. The other is engraved: like and like to join. This does not only apply to royal houses and ruling dynasties who like to marry among themselves and have thus established a kind of institutional inbreeding.

Blood relatives marriages are still common in many parts of the world. For example in North Africa, the Middle East and on the Indian subcontinent. However, marriage does not take place between brother and sister, but between people with an average degree of relationship, such as between cousins ​​and cousins. Usually the later partners did not grow up together, but only part of the same extended family or the same clan.

If the parents are not related, the risk of genetic disability is three percent. "In Iran, where around 40 percent of children come from marriages between blood relatives, it doubles or triples," estimates Hans-Hilger Ropers from the Max Planck Institute for Molecular Genetics in Berlin.

The incest taboo could not work for Patrick S. because he only got to know his sister as an adult. The “natural barrier” against a person who is similar to oneself was no longer there. He may now have to pay for being a victim of “genetic sexual attraction”. This means that some people meet close relatives with whom they did not grow up together - for example because they were adopted after their birth - and who now find each other extremely attractive. In the age of artificial insemination, this phenomenon of genetic attraction is likely to increase: an Oedipus complex for the 21st century.

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