Scientists have identified 52 genes associated with intelligence

Mankind knows very little about the biological basis of their mental abilities - it cannot even consistently agree on which method is best used to test them. But some things seem obvious. The first is that high scores on a number of standardized tests designed to measure the level of intelligence tend to correlate with the results we associate with intelligence, for example, with achievements at school or university. The second is that these high results are most likely largely due to genetics.

Previous studies have shown that the impact of any single gene on intelligence is not that great: studying relatively small groups of people, scientists could not detect a small group of genes that could theoretically affect intelligence. However, on May 22, 2017, a team of European and American scientists announced about making significant progress in learning mental abilities. Scientists have identified 52 genes associated with intelligence, almost 80 thousand people.
')
In their totality, these genes, again, have very little effect on intellectual abilities, but researchers still expect to discover thousands more. It should also not be forgotten that intelligence is also formed under the influence of the environment.

The team used open data from 13 different studies. Although the participants in the experiments were offered different tests, the researchers focused on measuring the general intelligence. The genome of these people was scanned to find differences in one basic pair, which allowed the authors to find a correlation between parts of the genome and the test results.

Two separate analyzes were performed. During the first one, the study authors simply examined separately each difference in the bases of the genome. In total, 336 bases were obtained, which were grouped in 22 different genes. In the second analysis, the authors tracked differences in bases that were grouped in a single gene. Since there are more markers for each gene, this is usually a more accurate way to find the desired effect. The team calculated that the genes identified during the first analysis increase or decrease the level of intelligence by less than 5%.

Experts believe that the results obtained will make it possible to begin new experiments on the biological basis of reasoning or problem solving. Potentially, they can help researchers determine which interventions will be most effective for children who are starting to learn.

Psychologists have been studying human intellect for over a century, asking people questions. Such a seemingly uncomplicated way of research turned into a battery of tests over time, each of which explores a specific aspect of intelligence, such as verbal reasoning or memorization.

In a typical test, the subject must present a rotating object, select one shape that complements the other, and press the button as soon as possible when a certain type of word appears. As a result, each person can get different marks for each ability. Usually, the assessment of some abilities is comparable to the points for others, and vice versa. Psychologists sometimes refer to this effect as general intelligence.

It is still not clear which part of the brain is responsible for intelligence. Neuroscientists compared people's brains with intelligence tests, and made several assumptions. The size of the brain explains small deviations, for example, there are many people whose brains are slightly smaller than usual, who score more points than people with normal or large brains. Other studies indicate that intelligence is related to how effectively the brain can send signals from one area to another.

Daniel Postuma (Danielle Posthuma), a geneticist at Amsterdam Free University and lead author of the latest study, first became interested in intelligence research in the 1990s. She wanted to find genes that affect intelligence, and for this purpose she began to study homozygous twins who shared the same DNA. She managed to find out that identical twins passed tests with more similar results than heterozygous ones.

Hundreds of other researchers led to the same conclusion, confirming the apparent influence of genetics on intelligence. But this does not mean that intellectual abilities are determined only at the genetic level. The environment also has certain effects, the mechanism of action of which modern science understands well. For example, lead in drinking water can reduce test results, and in places where food does not contain enough iodine, dietary supplements can increase scores in children.

Advances in DNA sequencing technology have increased the likelihood of a successful search for individual genes underlying the differences in intelligence tests. Some “candidates” were identified in small groups of the population, but their influence was not manifested in studies of large groups. Therefore, scientists turned to what is now called the study of association with the genome: they order fragments of genetic material scattered across the DNA of many unrelated people, and then look for people with high marks on an intelligence test with the same genetic markers.

In 2014, Dr. Postum became part of a large-scale study of more than 150 thousand people, which revealed 108 genes associated with schizophrenia. With intelligence, everything turned out to be much more complicated, and for several reasons.

Standard analytical tests take a long time, making it difficult to collect results from a huge number of people. Scientists may try to combine small studies, but they often have to combine different tests, potentially masking the effects of genes. As a result, the first generation of genome intelligence research found no genes. Later, researchers were able to identify promising results, but when they turned to other groups of people, the effect of genes again disappeared.

In the past few years, larger studies based on new statistical methods have finally provided convincing evidence that certain genes are actually involved in shaping human intelligence. Dr. Postum and other experts decided to combine data from 13 previous studies, forming an extensive database of genetic markers and intelligence tests.

The results were not long in coming: in addition to the already known 12 genes, 40 new ones were found, strongly associated with intelligence. Together, they constitute a small percentage of variation in intelligence tests — each option raises or lowers IQ by a relatively small number of points.

Christopher F. Chabris, co-author of the new study, is confident that many of the missing genes can be found through even larger studies involving hundreds of thousands, or even millions of people.

In his study, Dr. Postum and her colleagues limited their research to people of European descent, as this increased the chances of finding common variants of genes related to intelligence. Other gene studies have shown that variants in one population cannot predict what will happen to other populations. In different groups, different options may influence certain factors, among which may be the intellect.

“If you try to predict the height of a person with the help of the genes we have identified in Europeans, in Africans, then you will come to the conclusion that all Africans are five inches lower than Europeans, which is not true,” notes Dr. Postum. Studies like this recently published do not mean that intelligence is shaped by our genes. As an analogy, researchers cite myopia, which is highly dependent on genetics. But we can change the environment with glasses that improve people's vision.

Developments in the field of genetics of intelligence, scientists plan to use to find more effective ways to help children in intellectual development. Knowing the genetic variations of people will help them assess which parenting strategies will be most effective. Dr. Postuma, for his part, wants to understand the 52 genes found, since there are intriguing coincidences between their effect on intelligence and other traits. Genetic options that increase intelligence also often appear in people who have never smoked. Some of them are also common in people who smoked, but successfully quit.

What actually makes the genes and how they affect the intellect, scientists can not yet say. It is only known that four of them are responsible for the development of cells, and the other three do many interesting things inside neurons. To understand what makes these genes so special, scientists will have to experiment with brain cells. One possibility is to take cells from people with options that predict high and low levels of intelligence.

Postuma and her colleagues can make them grow into neurons, and then turn into "miniature brains" - clusters of neurons that exchange signals in the laboratory. Then researchers could see if their genetic differences lead to differences in behavior. “We cannot do it overnight, but I hope I can do it in the future,” noted Postuma.

doi: 10.1038 / ng.3869