Incest is a problem with people

incestLess risky than expected

Let's start with Charles Darwin. The natural scientist not only devised the theory of evolution, but also dealt with breeding experiments. "On the good influence of crossbreeding and the harmful effects of inbreeding," is a chapter heading in Darwin's book on plant and animal breeding. He himself was convinced that these results could also be transferred to humans. This worried him all his life, because Darwin had married Emma Wedgwood, his own cousin. Three of her ten children died early. But that wasn't unusual back then. With the resources of genome research, the influence of the parents' relatives can now be estimated much more precisely.

"We wanted to know whether it mattered if you inherit the same version of DNA from your father and mother. We focused on the diseases that most people die from, such as cardiovascular disease and diabetes Old age. " Jim Wilson from the University of Edinburgh has analyzed the data from a large number of health studies with over 350,000 participants in a new way. First of all, he had to determine the degree of relationship between the parents. It's via the DNA. It exists in two copies in every cell, one from the mother and the other from the father. There are innumerable places in the human genome that can exist in different variants.

No effect on cardiovascular diseases

"You go down the chromosomes and count: the same, the same, the same, and then there is a piece that came from dad and mom in different versions. We all have these same places on the DNA, because ultimately we are all related to one another Question is how long ago was that? " The length of the matching points on the DNA is a measure of the relationship. It is usually quite low. But that was only the first part of the study. It got interesting when Jim Wilson compared this genetic relationship with the health data. "We were amazed that there was no effect at all on metabolic or cardiovascular diseases. However, the degree of relationship has a clear influence on body size and mental performance."

This is exciting for Jim Wilson, because he is primarily interested in the influence of evolution on the human genome. From his data, he concludes that a large body and sharp mind were advantages in the struggle for survival. The common diseases, on the other hand, do not play a major role. Evolution depends on the offspring. And they usually stand on their own two feet when the heart attack or diabetes take their toll.

This is not noticeable in a German urban population

But back to the influence of relationship marriage on size and various aspects of mental performance. Here the effect can be clearly demonstrated statistically. But whether it is also relevant is a completely different matter. This can be seen if the data from the population are converted to hypothetical average children of cousins. "It's about rather small effects. These children would be 1.2 centimeters smaller and would achieve ten months less schooling. These effects are not noticeable in a German urban population. In areas with many relatives, things might look different."

As far as school education is concerned, one should not forget that social factors play an important role in addition to genetic factors, says Jim Wilson. Relatives marriages certainly cause problems with the rather rare real hereditary diseases. But when it comes to general health, the risk to the children doesn't seem to be as great as is often thought. Incidentally, in the end, Charles Darwin saw it that way too.

"The evidence for an evil created in this way is contradicting itself, but on the whole it suggests that it is very small."