Should the society be separated according to the IQ

Twin research: on the trail of intelligence

Interesting freak of nature

A test group couldn't look any better under laboratory conditions: Identical twins are like clones, i.e. genetically identical. They develop from a fertilized egg cell that divides in the first days of embryonic development. Twins share a uterus early in life and often spend the rest of their lives close together.

The genetic makeup may vary slightly, as researchers from the University of Alabama reported in 2008. This explains the fact that one twin can develop a disease while the other remains healthy. However, identical twins show the closest possible genetic match.

In the case of dizygotic twins, the resemblance is already greatly reduced; they are very similar to normal siblings. Their genetic similarity averages 50 percent. What makes them special, however, is that, unlike normal siblings, they grow up in parallel. So the environmental influences hit the siblings at the same time.

Influence of the common environment

Regardless of whether they are identical or dizygoti: As a rule, twins live in the same household. So they not only share the genes, but mostly also at home, school or environment. An exciting constellation, especially when it comes to the question of what influence genes have on certain characteristics such as intelligence and what role the environment plays in this.

If, for example, identical twins are more similar than dizygoti, this must be due to the greater genetic similarity. In a wider sense, this means: The influence of the environment plays a greater role when twins do not differ or differ only slightly. Because then environmental influences contribute to this similarity, for example the upbringing, the social and financial status or the cultural background.

Adoptive siblings can be just as exciting for research: If the siblings are actually similar in certain areas, this similarity must be due to shared environmental factors, since adoptive siblings are not genetically related to each other.

A comparison of the adopted children with their biological parents can be just as revealing for researchers: Since parents and children live separately, the genes must play a role in the case of similarities.

Born smart

What is more important for the development of intelligence - genes or environmental influences? The unsurprising answer: Both are important for cognitive development. But in the course of life the genes become more and more important. This has been studied very well in twin studies.

At birth, genes make up about 25 percent. In plain language this means: 25 percent of the differences in terms of cognitive skills / intelligence can be explained by genetic differences. When you start school it is already around 50 percent - and in later life the genes make up as much as 70 percent.

The older the twins get, the more genetic factors can explain differences, for example in intelligence tests.

The further the research advances, the more attention is currently shifting towards genes. "Nevertheless, training offers and educational measures are important because there is an interaction between the system and the environment," says Frank Spinath, Professor of Differential Psychology at Saarland University. This means that genes need a stimulating environment in order to be effective.

The search for the super gene

Which genes are exactly responsible for intelligence? Intensive research has been carried out on the intelligence genes since the mid-1990s. But the search is frustrating. "The flaw in the system: It was initially thought that the gene effects were stronger and that the number of intelligence genes was manageable," says Frank Spinath. "In fact, there are a lot of tiny effects. There are a lot of instruments in the intelligence concert."

The researchers realized that for a long time they had laid out the grid much too roughly for their investigations. Because these small effects can only be recorded with extremely large samples, i.e. with at least 200,000 people in a sample. And in some cases it is not even entire genes that correlate with intelligence, but often only genetic segments. These subtle differences can only be seen when the masses are compared.

Genes have an influence on intelligence, but in a complex interplay with many factors.

Hereditary, but not immutable

So, to a large extent, intelligence is already inherent in the cradle. The IQ allows a prediction of the opportunities for education and work - and thus also of the social and economic status that a person can possibly achieve. But that's not a reason to put your hands on your lap. Because without an appealing environment, the system cannot develop.

Take reading development as an example: Intelligent primary school students usually learn new letters and words quickly. But this ability must be encouraged so that the children can later read complicated texts and long books as adults.

So being born smart is not enough. From twin studies we know that in addition to cognitive abilities, personality traits also play a role when it comes to success: for example, motivation, tolerance to frustration or hard work.

It was also shown which parenting behavior particularly favors the school success of the offspring: Support and the push towards independence are helpful, while control and a lack of emotional warmth are counterproductive.

In general, the following applies: Those who are challenged and given demanding tasks learn better to reason or to solve problems. Nevertheless, one cannot significantly influence the IQ. In other words, grass doesn't grow faster if you pull on it. Not even if you are a twin.