Incestuous relationships cause diseases

It is one of the last great taboos. Only murder and cannibalism commonly cause even greater disgust than close relatives' sexual intercourse. Hardly anyone cares anymore when men love other men or women love other women. But consensual love between close blood relatives remains a criminal offense. One of the reasons: the offspring could not be healthy.

In fact, the offspring from incest relationships are often not the norm. The parents' genes are too similar. All the little flaws that every person carries in their genetic make-up are not noticeable when you look around the wide world for a partner. Everyone has around six defective genes. But he also has two versions of each genetic make-up. So there is usually still a healthy gene that makes up for the mistake in its inadequate double.

The problem with siblings: They are half genetically identical. If they have children together, they may be passing on the same faulty gene. "The risk that the next generation will be disabled is very high," says Arne Pfeufer, human geneticist at the Technical University of Munich. In the largest study on the subject, a Czech geneticist recorded 161 children from incest relationships - 44 percent of them were mentally disabled, two thirds of them were severe.

"The risk could be overestimated"

"The risk could be overestimated, however, because people who come together for such incestuous connections are not representative," says Peter Propping, President of the German Society for Human Genetics. "Usually at least one parent is mentally retarded." That probably also applies to the siblings from Saxony. Two of their four children are said to be less intelligent. But is that because of the incest? Both parents also only attended special school, the mother is certified as having a lack of intellectual maturity.

No matter how high the health risk for the offspring may be, the Heidelberg geneticist Claus Bartram may not accept the medical justification for the Karlsruhe judgment. "There are hundreds of hereditary diseases in the population that pose an equally high risk for the children," says the professor. "It would never occur to anyone to forbid such people from reproducing." Rather, it will be left to those affected to decide for themselves. "

Close familiarity as a love killer

The fact that the incest ban remains in place is probably due to the emotions that the topic triggers, says Arne Pfeufer. After all, hardly anyone can imagine ending up in bed with their closest relatives.

Close familiarity kills all sexual desire, anthropologists postulated a hundred years ago. The Simpua marriages in Taiwan are evidence of this. There, promised toddlers grow up together in the groom's house. Their marriages are often childless.

The kibbutzim in Israel have also proven to be love killers. Children who have lived together there from birth almost never marry, as Israeli anthropologists found out. So physical sibling love will hardly become a mass phenomenon, even if all incest paragraphs disappear in all statutes of the world.