Intelligence (from Latin intellegere "recognize", "see"; "understand"; literally "choose between ..." from Latin inter "between" and casual "read, choose") is a collective term in psychology for cognitive or spiritual Efficiency. Since individual cognitive abilities can be developed to different degrees and there is no consensus on how to determine and differentiate them, there is no general definition of intelligence. Rather, the various intelligence theories suggest different operationalizations of the everyday term.
General psychology , differential psychology and neuropsychology deal with intelligence . Research into intelligence in the field of general psychology under the aspect of information processing is now often referred to as cognitive psychology . This in turn draws on methods and findings from brain research , developmental psychology and, increasingly, artificial intelligence .
General factor of intelligence according to Spearman
The g-factor of intelligence (g-factor) introduced by Charles Spearman is one of the most widely used measures of general intelligence . It is one of the most reliable and most valid constructs in psychology.
According to Robert Plomin , he predicts school success and prestige of the profession later achieved better than any other measurable quality. Its predictive power on variables such as occupational prestige and income of an individual is diminished when one includes a correlated variable of the socio-economic status of the parental home. In this case, too, he makes an independent contribution to the explanation of variance .
It is undisputed that people are more similar to their relatives with regard to the g-factor than randomly selected people. However, it is unclear to what extent biological or social factors are the cause of this similarity. This question is one of the most widely discussed questions in psychology. While today there is broad consensus that both factors play a role under normal conditions, there is considerable disagreement about how strong the influence of which factor is. This conflict is referred to in English as "Nature versus Nurture" (English "nature" for nature in the sense of the genetic component and English "nurture" for education in the sense of social factors).
The representatives who assume that the g-factor is strongly influenced by hereditary factors are known as Hereditarians . On the other hand, environmentalists are those who support the thesis that the g-factor is largely due to environmental influences. Today there is an abundance of studies on the hereditary nature of the g-factor, but these are interpreted differently by different camps. The interpretation is made more difficult by the fact that the heritability of the g-factor is not the same under all conditions.
The debate about the hereditary nature of the intelligence has not remained free of scandals. Cyril Burt , for example , who assumed a heredity of intelligence of 70 to 80%, and Rick Heber , who, on the basis of an experiment whose existence have been questioned, assumed that the intelligence quotient could be increased by around 35 points through appropriate programs, are controversial let increase. Cyril Burt was suspected of falsifying data by Leon J. Kamin . It is now undisputed that Burt's data on twin research from the first half of the 20th century cannot be used. Whether it is a fake or negligent research is controversial among scientists. Burt's student Hans Jürgen Eysenck felt that Burt was negligent, but did not fake it. He did not consider all of Burt's work to be unusable, only those on twin research, and resorted to others. Although these researchers are considered extremely controversial today, they are still (as of 2009) by other scientists from the corresponding camps, e.g. Some cited uncritically.
Differential psychology and psychological diagnostics
The differential and personality psychology is the source of much of the research to construct intelligence. In this discipline, intelligence is seen as a sub-area of personality in the broader sense. In doing so, one tries to avoid the fuzzy terminology that is used in everyday language ( thinking , comprehension , rationality , logic , judgment ) in order to characterize the mental abilities of humans, to make intelligence measurable and of other constructs of psychological research such as B. To delimit creativity (see discriminant validity , test quality criteria ).
Intelligence diagnostics or psychometry emerges as an area of application from the basic discipline of differential psychology . Here one tries to determine quantitative differences in intelligence between people. As a technical term in psychometry, "intelligence" was coined around 1900, with the impetus coming from the French ( Alfred Binet ) and English-speaking areas ( Louis Leon Thurstone , Charles Spearman ). Some intelligence tests are adaptive and adapt to the level of difficulty of the subject (so-called adaptive testing ).
An intelligence test is used to record a person's cognitive abilities . There are many different tests for different target groups and use cases. The result of such a test is often the so-called intelligence quotient (IQ).
Intelligence tests are based on the assumption that the population's intelligence quotient is normally distributed . The IQ thus describes the deviation from the mean value 100, a standard deviation is 15 IQ points.
The Validitätsnachweis of intelligence measurements is to use a pre-requisite, such results in the psycho-diagnostic practice.
In 1904 a society for child psychology , the Société Libre pour l'Etude Psychologique de l'Enfant , was commissioned by the French government to create a test to identify mentally handicapped children who no longer benefit from normal schooling. Alfred Binet and Théodore Simon then developed the first IQ test. The IQ was defined as the quotient of intelligence age and age.
Later, other researchers ( David Wechsler ) introduced a new intelligence concept in which the performance of the individual is related to the mean value of the corresponding age group.
The author of the first intelligence test, Alfred Binet, saw intelligence as a bundle of numerous individual abilities, even if his test seemed to show that intelligence was something uniform, whole. However, he did not create a more precise structural model.
In the course of time, various explanatory models emerged, which mainly rely on factor analysis .
Intelligence as a personality trait
Intelligence correlates with a number of other variables. Intelligent people are often more successful at school than less intelligent people and, on average, occupy higher professional positions (this applies in particular to men, whose IQ value correlates around 0.7 with professional prestige, for women the correlation is lower due to child-rearing, among other things). Among students and trainees, the more intelligent perform better than the less intelligent. Above-average gifted people usually live healthier lives and have a longer life expectancy.
It could be shown that, at least in the USA, social background has a much stronger influence on earnings than intelligence.
However, intelligence also correlates with disease. For example, intelligent people are more likely to be nearsighted. There is also a connection with certain hereditary diseases.
For mental disorders such as schizophrenia , it could be shown that both particularly intelligent and particularly less intelligent people suffer more from it - but that are on average intelligent far less often.
It is statistically proven that intelligence and brain volume are positively related.
Criticism of the concept of intelligence
Intelligence is often criticized as a statistical construct. There is a strong connection between IQ and social class. Members of the lower social classes and their children achieve a lower IQ on standardized intelligence tests than people from the upper social classes and their children. It is discussed whether this is because traditional intelligence tests are unfair towards workers and their children, and IQ tests have therefore been criticized as classic . In addition, there seems to be an operationally distinguishable ability from intelligence to guess the correct answer from the formulation of the test ( test-wiseness ). This applies in particular to multi- choice questionnaires . It is also possible that familiarity with the form of questionnaire tests or with classic intelligence test tasks trains test-wiseness as well as the specifically queried cognitive abilities or the mere response speed.
Regression to the middle
Already Francis Galton noted first that the intelligence levels of children to their parents a " regression to the mean " (regression to the mean) have, which means that they are approaching the average. Children of the gifted and highly gifted are on average not quite as intelligent as their parents, but their intelligence is somewhat lower (although still above average). In contrast, the children of below-average people are, on average, slightly more intelligent than their parents (though still below average).
In psychology today there is broad consensus that both heredity and environmental influences play a role in intelligence development.
Numerous studies support estimates that 30 to 80% of the total variance (total variation ) in general intelligence can be explained by genetic factors. The heritability of intelligence, i.e. the proportion that is based on genetic influences, increases with age, from around 30% in early childhood to 70 to 80% in adulthood. This increase in the heritability of intelligence with age could be due to the fact that adults have a greater tendency than children to choose and shape their environment according to their genotype, thus amplifying genetic differences. James R. Flynn explains it with interactions: originally relatively small inherited differences lead to different experiences that reinforce these differences. A name of its own was even suggested for the finding: Wilson effect (named after the behavioral geneticist Ronald S. Wilson (1933–1986)). The effect is most pronounced in young adult years, but can be demonstrated well into old age.
Numerous researchers are of the opinion that intelligence always has a hereditary component, since “the meta-analysis by Bouchard and McGue (1981), which is now to be regarded as classic, the empirical search for the answer to the question of whether general intelligence is hereditary with a clear one 'Yes' ”.
Other authors also point out that the relevant environmental influences can usually not be identified in more detail and that these are environmental aspects that are not shared within the family, i.e. those that affect siblings growing up together in different ways, for example.
“The various approaches to investigating the hereditary nature of intelligence do not produce completely consistent results. The highest heredity estimates of around h (2) = 70% resulted from studies on identical twins raised separately, while both the comparison of identical twins with dizygotic twins and adoption studies yielded heredity estimates that are closer to h (2) = 50%, sometimes even below . There is no doubt, however, that the findings converge to the effect that individual differences in IQ are, to a large extent, genetically determined. Furthermore, the findings converge to the effect that the different quality of the family environment contributes to individual differences in intelligence. The estimates for c (2) fluctuate between 20% and 40%. "
- Note on the quote: The expression h (2) is the genetic symbol of heritability, c (2) stands for the social factors and influences.
Richard Lewontin argues that the opinion that intelligence is largely hereditary and that environmental influences are not to be found within the family came about through incorrect interpretation of adoption studies. If the studies are interpreted correctly, it is obvious that the family environment shared by siblings plays a major role.
Lewontin explains this thesis with a parable:
“Imagine having a sack full of wheat grains. Divide this sack in half at random. One half would be sown in fertile soil that was well watered and fertilized. The other half is thrown into a barren field.
If you now look at the first field, you will notice that the ears of wheat are of different sizes. One can trace this back to the genes, because the environment was the same for all ears.
If you look at the second field, you will be able to attribute the variation within the field to the genes.
But it will also be noticeable that there are big differences between the first field and the second field. In the first field the differences are 100% genetic, in the second field the differences are 100% genetic, but that does not mean that the differences between field 1 and field 2 are also genetic. "
Lewontin sees it in the same way with the social environment: the IQ differences within a stratum can be genetic to a certain extent, but this would not mean that the differences between two strata also have to be genetic. As evidence he cites adoption studies, for example those by Skodak and Skeels or the Minnesota Transracial Adoption Study.
As an analogy, he also cites body size, which is known to be largely genetic. However, this cause can only be regarded as sufficient within one class, but there is still a difference between different social classes, which today is given as three to four centimeters. With increasing economic prosperity, the size of entire nations also increases.
Borkenau criticizes Lewontin's assessment as inaccurate and generalized:
“[It is] not appropriate to pick out the study that implies the lowest or highest heredity estimate, at will, and rate that study as the most conclusive. This is the way [t] [...] Lewontin [...] proceeds. "
Furthermore, Rainer Riemann and Frank Spinath pointed out that the share of heredity in children and adults is different from what Lewontin claims:
“Apparently the environmental conditions shared by family members only have an effect on intelligence until the people leave the family. [...] While effects of the shared environment explain a quarter of the variation in intelligence in childhood, these can no longer be demonstrated in adulthood. However, the influences of the specific environment are increasing. "
Risk Factors in Childhood
* These are IQ values based on a US scale
So-called risk factors , such as the parents' drug use, poverty or poor mental health of the parenting person, can have a significant negative influence on the development of intelligence. One study found that child development is only severely impaired when several risk factors occur at the same time.
The quantitative results of this study are shown in the table.
Another longitudinal study came to the same conclusion. One or two risk factors had very little effect on cognitive development, but when others were added, the effects were strong. Children who were affected by eight to nine risk factors even had an IQ that was on average 30 points lower than children with no stress.
Studies of adopted children make it possible to examine the influence of the social environment on a child's intelligence development. Since the adopted children are not related to their parents and siblings, their IQ would have to be independent of that of the adopting family with a purely inherited intelligence. However, if only the socio-economic environment influences the development of intelligence, there should be no significant difference in IQ between the adopted child and his adoptive parents or siblings.
The Minnesota Transracial Adoption Study , begun in 1975, was a methodologically complex, large-scale, and well-documented study of the adoption of children from families of the lower and working classes who were adopted by families of the upper middle class. At the beginning of the study, both the adoptive parents and their biological children were tested when the adopted children were 7 years old. The IQ of the birth parents was not recorded, only their education, on the basis of which the average IQ was estimated at around 85 to 90. 10 years later, all candidates who could still be localized were tested again with another test (the results are slightly lower due to the test).
Overall, it becomes clear that the adopted children are very similar in the IQ to their adoptive parents and siblings:
* The GPA corresponds to the grade point average, whereby 4.0 corresponds to the German 1.0.
Based on the data that were obtained when the candidates were 17 years old, a correlation with the education of the biological mother (but not that of the biological father) could be shown (factor: 0.23). Furthermore, a significant correlation with the age at which the child was given up for adoption was found: the younger it was, the more intelligent it was later (−0.30). While no connection to the adoptive parents' income or education was found, their intelligence quotients were decisive (father: 0.20, mother: 0.18). The “quality of the foster family before adoption” also correlated (0.30). This shows how much a child's intelligence depends on their social environment.
The authors Scarr and Weinberg explain the poorer performance of black children with racial discrimination and the fact that many were only given up for adoption at an older age. Eyferth's study also suggests the great influence of environmental factors on the results. With regard to bi-ethnic children, there is the comparative study carried out in Germany by the psychologist Klaus Eyferth from 1959, who tested the average intelligence of 264 “occupation children”, i.e. children of a German mother and white or African-American soldiers stationed in Germany determined:
The research shows that there was no significant difference between children with two white parents and children with one black and one white parent. While it is often criticized that the black soldiers were not representatives of the Afro-American population because they were possibly intelligent above average due to the selection criteria of the US Army (based on their ethnicity), the army's test result protocols showed that black soldiers were on average achieved lower IQ values than white soldiers, which also corresponds to the overall picture of the US-American intelligence distribution. In 1980, Flynn drew the conclusion after extensive analysis that even selection criteria (from the US Army) could not explain this result and noted that there must have been substantial differences in intelligence between the white and Afro-American fathers involved, which, contrary to expectations, had no influence on the intelligence of the two groups of children.
Adoption studies by Clark and Hanisee (1982) and Winick, Meyer and Harris (1975) also suggest the relationship between the child's intelligence and his or her social environment: It was shown that Vietnamese and Korean orphans raised by American middle-class families later had an above-average IQ. In the studies it was on average between 112 and 120 for adequately nourished children. Malnourished children had an average IQ of around 102 to 106. Orphans who were raised by relatives in Vietnam or raised in homes, on the other hand, had a below-average IQ.
In a French adoption study it was shown that even through comparatively late adoption, combined with an improvement in the social environment, the IQ of a neglected / abused child who was below average intelligent before adoption can be increased. It was also shown that children who were adopted by families with a high socio-economic status developed a higher level of intelligence (IQ average: 98) than children who were adopted by families with a low socio-economic status (IQ average: 85).
The adoption study by Harold M. Skeels and Skodak is also much cited. These originally examined 181 adoptive children for their IQ. They followed their mental development up to adolescence . At this point in time there were still 100 people in the sample. They came to the following results:
- Adopted children develop very favorably compared to their birth mothers.
- Children adopted by middle-class couples have an IQ equal to that of the biological children of this class.
- The IQ of the biological mother correlates clearly with the IQ of her child. Children born to birth mothers with an IQ of less than 70 had an average IQ of 104 in adolescence. Children born to birth mothers with an IQ of 110 or more had an average IQ of 129 in adolescence. However, it is not certain whether this is due to biological factors, since it was American adoption practice at the time to place the children of the most intelligent mothers in the richest adoption applicants.
- Emotional and personal factors play an important role in intellectual development in the adoptive family.
An adoption study conducted by Capron and Duyme came to the conclusion that both genes and the environment play a role. In the vast majority of cases, the biological parents of adopted children come from the poor. Little is known about the adopted children whose birth parents are wealthy. The adoptive parents, however, mostly come from the upper classes, if only because poor people are rarely allowed to adopt a child. In order to close this knowledge gap, Capron and Duyme were now specifically looking for children with wealthy birth parents and also children with poor adoptive parents.
It could be shown that three groups of children achieved an IQ above 100:
- Children who had both wealthy birth and wealthy adoptive parents,
- Children who had poor birth parents and wealthy adoptive parents,
- Children who had wealthy birth parents and poor adoptive parents.
In contrast, achieved an IQ of less than 100:
- Children who had both poor birth and poor adoptive parents.
The following table shows the results in detail:
It has been criticized, however, that the heredity of the IQ is overestimated, as a majority of adoptive parents are "white, of legal age, wealthy, educated and living in stable marriage". This means that the adopting families do not have the full spectrum of environmental influences. The environment in these families is usually particularly conducive to IQ development, so that one can only conclude from the low influence of the environment in these studies that it does not matter whether a child is in the educated, affluent couple A or the educated , wealthy couple B growing up.
A connection with the development of intelligence has been demonstrated for some genes. However, the influence of individual genes is relatively small. It is also controversial whether the findings are reproducible.
Intelligence is not determined by a single master gene or just a small group of genes, but is a multi-genetic disposition. Using the SNP - microarray technology 47 gene sequences were identified in total, which correlated with the development of intelligence. However, none of these gene variants contribute more than 0.4% to intelligence, the six most influential gene variants taken together only contribute a little more than 1% to the development of the intelligence of an individual. Since a person's intelligence is closely linked to the brain and at least half of the genome contributes to its individual structure, the researchers suspect a large number of other genes. Other scientists found slightly more influential gene variants. This could explain up to 3% of the IQ. A master gene could not be found.
A correlation could be demonstrated for the following genes, among others:
- One of six variants of the DTNBP1 gene , responsible for the production of the protein dysbindin-1 , appears to lower intelligence. At the same time, there is likely to be a link with schizophrenia . The mean IQ of people with this gene variant is 3 points below the mean for the entire population.
- A certain variant of the receptor gene for the insulin-like growth hormone IGF-2 seems to occur in gifted children with 50% about twice as often as in normally gifted children (25%). However, this only explains a difference in IQ of around 4 points. Compared to others, this variant is associated with more frequent nearsightedness and the occurrence of allergies as well as tall stature and a slim body shape.
- For some variations of the COMT gene, a connection with slightly increased intelligence could be demonstrated. At the same time, it is also linked to schizophrenia.
- Also polymorphisms in the interleukin-1β gene may have an impact on intelligence subjects to genotype had CC, are smarter than the rest of the population, according to a study.
- The CHRM2 gene is currently the favored gene when it comes to the influence of genes on intelligence and academic performance. It was found that some variations in the CHRM2 gene lead to increased intelligence. It was also found that these variations of the gene have a positive influence on the level of education achieved. However, the influence of each individual variation is very small. However, the cumulative impact of all the variations in this gene taken together could be far greater.
- We are currently investigating the two cases where a person has all or all of the intelligence-enhancing or all intelligence-impairing variations in the CHRM2 gene. It is believed that in this rare case there would be significant IQ differences. Presumably a person with all intelligence-enhancing variations would outperform a person with all intelligence-reducing variations by 15 to 20 IQ points. However, people who only have intelligence-enhancing versions or only intelligence-reducing versions of the gene are extremely rare, and the statements about this small group of people have so far been pure speculation.
Influence of the socio-economic environment
In all studies on the topic, class-specific differences in the intelligence of young people were found. However, these are not equally pronounced everywhere: the differences in rural areas are far smaller than those in cities. The exact reasons for this are unknown. It is assumed that lower-class milieus are developing more strongly in cities than in rural areas and that social problems such as unemployment and drug use contribute to the fact that children are not adequately supported.
There are no direct studies for Germany. However, the PISA study examined “problem-solving skills”, which is very similar to intelligence. Here, too, it was found that the differences between the classes were smaller in the countryside than in the city. There were strong differences between East and West Germany. In eastern Germany, young people from different social classes are much more similar in terms of their problem-solving skills than in the west. The reasons for this are unclear.
The social class also has an influence on intelligence. This shows that intelligence tests that make high linguistic requirements determine a greater connection with intelligence than intelligence tests that only have low verbal requirements. Such tests are referred to as culture fair tests .
Turkheimer has pointed out that social class plays a major role in the inheritance of intelligence. While intelligence in the middle class is largely hereditary, it is not so in the lower class . Twin studies have so far mainly been carried out in the middle and upper classes and have thus led to a result that does not take into account the greater importance of the environment in the lower classes. The poor environmental conditions in the lower class meant that the children could not develop their genetically given potential. On a scale from 0.00 to 1.00, the IQ in the middle class is 0.72 determined by genes, but only 0.10 in the lower class, according to Turkheimer.
Hertzig, Birch, Richardson and Tizard found in 1972 that malnutrition in early childhood has serious consequences for the intelligence development and social behavior of children. They examined children who were hospitalized for malnutrition and then returned to their families. Their mean IQ was 58. Clark and Hanisee studied the life paths of children adopted from developing countries who were malnourished and had traumatic childhood experiences. The children were adopted by upper-middle-class American families. Contrary to the assumption that these children would suffer from severe impairments, they turned out to be above average intelligent and above average socially competent. They achieved an IQ of 120 in the Peabody Picture Vocabulary Test , and an average of 137 points on the Vineland Social Maturity Scale. 100 points are considered to be average, 137 as extremely good. Clark and Hanisee came to the conclusion that malnourished and traumatized children prove to be surprisingly resilient when they are adopted into stable family relationships. Winick, Meyer, and Harris studied Korean adopted children who were adopted by American couples under the age of three. They divided the children into three groups: one severely malnourished, borderline and one adequately nourished. The severely malnourished group achieved an IQ of 102, the borderline cases an IQ of 106 and 112 the children who were not malnourished. Winick Meyer and Harris concluded that malnutrition in early childhood has a detrimental effect on IQ development, but that it is by no means condemned to a life with intellectual disabilities. If they are adopted by the age of three at the latest, even severely malnourished children will achieve a normal IQ. The above-average IQ values of sufficiently nourished children are probably explained by the adoptive families. Families that are allowed to adopt a child usually have a high socio-economic status and can offer the children particularly good living conditions.
It has long been known that iodine deficiency can lead to intellectual deficiency in pregnancy or early childhood. A meta-analysis from 10 different clinical studies showed that chronic iodine deficiency led to a mean IQ reduction of 13.5 points. Studies from all parts of the world have shown that chronic iodine deficiency leads to a reduced intelligence in children. Iodine deficiency is considered the world's greatest single cause of preventable brain damage and mental retardation (the world's largest single cause of preventable brain damage and mental disabilities).
The IQ of elementary school children from the USA could be increased through vitamin tablets. The experiment was made in two elementary schools, the majority of which were Hispanic students . The experimental group was given vitamin tablets, the control group received a placebo. The average IQ of the test group increased by 2.5 points.
Diet during pregnancy can have a positive effect on IQ. In one study, the children of women who received fish oil capsules during pregnancy were smarter than the children of women who received a placebo. Mothers who ate a lot of fish during pregnancy have children with higher IQs and better social behaviors than other mothers. The effect is also retained if other variables (such as social class or whether the mother was breastfeeding) are checked. However, some types of fish are highly polluted with mercury due to increasing environmental pollution . These should be avoided during pregnancy. In addition, care should be taken during pregnancy that enough iodine is consumed, as iodine deficiency during pregnancy can lead to a decrease in IQ in the child. In addition to a basic diet rich in iodine, such as fish, seafood and some vegetables, the supplementary intake of 100 (to 150) μg iodine per day in tablet form is recommended.
Initially, this does not rule out that upbringing is one of these environmental influences, since research on parenting styles shows that the same parents raise their individual children differently. Proponents of the heritage standpoint, however, interpret this in such a way that parents of several children react differently to the different genetically determined temperaments of their different children (cf. reciprocal interactionism ).
The complexity of the interaction between genetic material and the environment was evident early on from experiments on the inheritance of learning achievements that are now classified as classic. Rats were initially exposed to so-called disruptive selection pressure with the aim of changing their learning performance when crossing a maze. Over seven generations - while maintaining the same keeping conditions - on the one hand only the offspring of those mothers who learned to cross the labyrinth particularly quickly in the breeding line of the "clever" rats were bred . At the same time, in a second breeding line, starting from the same initial population, the offspring of those mothers who learned to cross the labyrinth particularly slowly were bred. Finally, it was possible to demonstrate statistically significant differences between the test animals of the two breeding lines: As a result of the removal of the unsuitable test animals from the breeding program, changes in learning ability had resulted which could only be explained by a change in the gene pool of the two breeding lines; the rats' ability to learn has a genetic basis. Robert Rosenthal , on the other hand, considered a different explanation: He argued that it may have been a so-called experimenter effect. In an experiment, he analyzed the behavior of researchers who allegedly had to test "clever" and "stupid" rats. The result was that the test animals selected purely at random showed strong differences in the extent of their behavior expected by the investigator. Rosenthal attributed this to an unconscious stronger affection for the supposedly smarter rats.
A few years later, a further study on animals of such “intelligent” or “unintelligent” breeding lines revealed that the genes only determine the rats' learning behavior under certain environmental conditions. Test animals from a slowly learning breed line were raised and kept in cages that were particularly varied with tunnels, slides and toys; conversely, test animals from the fast-learning breed line were housed in a particularly low-irritation environment: under these changed environmental conditions, no difference between the two breeding lines was detectable. With an unchanged gene pool in each of the two breeding lines, this is evidence that the environment has a decisive influence on learning performance in the labyrinth. The authors of the study therefore argued that only the interaction of heritage and environment produces visible behavior and that a separation into innate and acquired is ultimately neither meaningful nor possible.
Longitudinal studies show that there are clear intelligence differences between children whose parents value intellectual performance and children of parents who do not. The first group of children were more intelligent. Another study shows that the children of parents who showed a warm and democratic upbringing behavior were more intelligent than children of parents who behaved in an authoritarian and punitive manner.
According to René A. Spitz , neglect in early childhood can lead to hospitalism . This is characterized, among other things, by mental retardation and a low IQ. However, hospitalism is curable if the child is lovingly cared for later. Also of interest in this context are Harry Harlow's experiments with young rhesus monkeys and Harold M. Skeels' research on the development of intelligence in people who grew up in homes.
The language environment also plays an important role and is closely correlated with the social status of the parents. One study found that middle- and upper-class parents spoke to their children much more frequently and significantly more than those from the lower-class, and that they formed more complex sentences. According to the authors, this has an enormous influence on the development of intelligence; the IQ of the disadvantaged children averaged 79, while the socially well-off children who were talked to a lot averaged 117.
Children from poor backgrounds are often less intelligent, have poorer language skills and develop poorer social skills. In a 1997 study in the United States, the IQ of children from particularly poor households who earned less than half the poverty line was 6 to 13 points lower than those who earned about double the poverty line. 80–90% of the children in schools for people with learning disabilities come from a poor environment. According to Schlack, the insecure professional and financial situation of the parents, poor living conditions, life in socially disadvantaged areas, incomplete families, restricted and one-sided suggestions and social isolation contribute to the fact that the needs of children cannot be satisfied in this living environment. This leads to the fact that they cannot reach their intellectual potential.
Malnutrition and malnutrition is a major factor. Providing healthy nutrition to young children can reduce the impact of poverty on IQ. Possibly the influence of poverty on intelligence is mainly due to environmental developmental disorders of the child's brain, which can be detected in the MRI image.
But there are exceptions to the rule that poverty leads to low intelligence. For example, the Oakland Growth and Berkeley Guidance Studies did not show any significant effects of poverty among working- and middle-class boys. Poor middle-class boys had an average IQ of 115.9 and poor upper-class boys had an average IQ of 113.1. The results of these studies, which deal with individuals born in California between 1920 and 1929, cannot be fully applied to the present day. These are also boys who, despite poverty, grew up in a relatively good social environment.
Stability of intelligence
In toddlers up to around four years of age, intelligence is still very unstable, so that intrapersonal prognoses are not useful. The correlation for the age range from one to five years is only r = .18. From the age of three, the predictions become more reliable. From adulthood, the stability of intelligence is very high. Correlations from r = .89 to r = .96 can be demonstrated for a period of seven years.
In 1932, 87,498 Scottish children between the ages of ten and a half to eleven and a half were tested for the Moray House Intelligence Test . The aim was to identify working class children who could benefit from further education at the grammar school . After the turn of the millennium, the test participants who were still alive (who were now 80 years old) were given another intelligence test. The correlation was high with r = .66.
Alcohol consumption by the mother during pregnancy can cause fetal alcohol syndrome , also called FAS or alcohol embryopathy. This is often associated with low IQ scores. Fetal alcohol syndrome is the most common type of intellectual disability that is not genetic.
Scientists assume that environmental pollution, in particular from lead exposure, adversely affects the intellectual development of adolescent children.
Differences in the intelligence test
The intelligence test values in the population roughly follow a normal distribution , with the exception of a slight overhang at the lower end, triggered by severe cognitive disorders. The male intelligence distribution has a slightly higher variance , i.e. a higher proportion of men with extremely high and extremely low intelligence.
In industrialized countries, increases in the average IQ test results were observed up to the 1990s (the so-called Flynn effect ). Since the 1990s, the IQ has stagnated or decreased in some industrialized countries, while it is now increasing again significantly.
IQ differences between ethnic groups
The intelligence debate in the United States is characterized by two research findings:
- Ethnic groups differ in terms of their average IQ
- Groups that score high on intelligence tests are on average more successful in school and have a higher average income
However, it is contested by some people that IQ tests provide an objective picture of the skills of people from all ethnic groups. You are accused of standardizing mainstream American cultural beliefs. According to some scientists, even non-culture tests discriminate against members of minorities. In the USA, for example, it was decided in the "Larry P. v. Riles" case that IQ tests may not be used to assign African American children to special school classes, as they discriminated against them.
Rushton & Jensen (2005) wrote that most studies in the United States deal with black and white self-determination. The studies show that the difference between black and white IQ scores is around 15 to 18 points, or 1 to 1.1 standard deviations, which means that around 11 to 16% of the black population have IQ scores above 100 (the median of the total population).
Evolutionary biologist Richard Lewontin, psychologist Leon J. Kamin, and neurobiologist Steven P. Rose argued in 1987 that intelligence is a selective advantage in any setting , that it would be illogical for certain ethnic groups to evolve to be more intelligent than others. Rather, it is noticeable that differences in intelligence between different groups within a stratum are practically non-existent. The fact that some ethnic groups perform worse than others in IQ tests is therefore attributed by many scientists to the fact that an above-average number of people from these ethnic groups belong to the social lower class. Poverty, however, can lead to a loss of IQ and is therefore blamed by many scientists for IQ differences between ethnic groups.
In 1994, Herrnstein and Murray wrote their controversial book The Bell Curve . In this they again advocated the thesis that there are genetic IQ differences between the races. Elsbeth Stern and Ilonca Hardy commented as follows:
- »Herrnstein and Murray (1994) wrote a much-cited book on the subject, in which they tried to prove, mainly by re-analyzing existing data sets, that it was not the unfavorable living conditions of the black US population that were responsible for their poor performance in the IQ test, but the Genetically determined low IQ causes their poor economic situation. At a first, uncritical look, some statistical analyzes appear convincing, but on closer inspection, many arguments collapse. In a book published by Fraser (1995), numerous experts take a critical position. In particular, Nisbett (1995) criticizes the fact that Herrnstein and Murray ignore the many studies that show that Americans of African descent who transferred to a good school or participated in special training programs recorded considerable gains in IQ. "
Philip Zimbardo and Richard Gerrig share this argument . They emphasize that the fact that the IQ is highly hereditary within a group does not indicate that group differences also came about through genes:
- »Heredity estimates refer to estimates within a group. They cannot be used to interpret group differences, no matter how great the difference between groups in objective tests. […] The fact that an ethnic minority scores lower than another group on an IQ test does not mean that the group difference is genetic, even if the heredity estimate within the group is high. "
The Germany-wide intelligence tests of the district military replacement offices from 1998 were used in a study . As a result, there were far above average test results in the district military replacement office districts of Stuttgart and Chemnitz and in almost every second Bavarian district military replacement office district. In contrast, conscripts in the federal states of Brandenburg and Saxony-Anhalt did particularly poorly.
In Germany, a statement by Dieter Lenzen , President of the Free University of Berlin, caused a stir. He said that according to a study, Turkish immigrants to Germany could be less intelligent than Germans on average. The study used non-linguistic, figural tasks in order not to discriminate against the Turkish students simply because of the language. Nobody claims that immigrant children are stupid from birth, says Lenzen. However, in the study they demonstrably lagged behind the German children. This study gives no reason for racist speculation. Nor is it about genes. Rather, one thing in particular emerges from the study: "The school support for immigrants must do more than pure language support [...] School support must also compensate for cognitive deficits that are based on the social origin of the children."
According to learning psychologist Elsbeth Stern, the fact that Turks do worse in IQ tests does not mean that they are more stupid. "When Germany brought Turks into the country, it mainly needed people who were on the assembly line, that is, people from the poorly educated lower class." The poor performance of the Turks was primarily social - not ethnic. In addition, one can ultimately never hide the environment in intelligence tests. “The test used primarily requires that one recognizes logical structures in sequence of figures. For example, those who play a lot with puzzles at home have an advantage over other children ”.
Intelligence researcher John Ogbu was able to show that social stigmatization of an ethnic group or caste leads to poor performance on IQ tests. For example, the Japanese Burakumin have an IQ 15 points lower than other Japanese.
Richard E. Nisbett has examined three socially and academically above-average ethnic groups in the United States - Americans with an Asian background (Asian-Americans) , Blacks from the Caribbean (West Indian Blacks), and Jews - who differed both in terms of geographic origin and origin very different from their history. Aside from the energy required to immigrate and start over (immigrant drive) , what the three groups have in common is that they attach great importance to hard work, upbringing and encouragement of children and that individuals who are successful in this way are respected rather than envied become. In Nisbett's words: “Intelligence and academic achievement are very much under people's control.” (Intelligence and academic achievement can be controlled very well by people) .
Between men and women
There are cognitive tasks in which men do better as well as those in which women do better: men primarily in mathematical tasks and those that concern spatial thinking, women in language-related tasks. Both achieve the same mean values on average in intelligence tests. This can be explained by the fact that this result is desired by the test designers: Tasks in which men or women do better are weighted in the test in such a way that they balance each other out.
According to some studies, men and women have, on average, the same mathematical intelligence. In a series of studies that were carried out on about 3 million randomly selected subjects, on average, similar skills were found. It was noticeable that the men were in the majority of both the very talented and the extremely untalented individuals. This is seen by some researchers as a possible reason why there are more eminent mathematicians than women mathematicians. Here, of course, it must be taken into account that women had no access to universities for a long time and were otherwise socially disadvantaged. In addition, these differences do not occur in all ethnic groups and nations and, according to some scholars, depend on the degree of social equality between men and women. Other studies, however, in accordance with the "classic" results of educational research, showed a certain advantage for men in standardized tests of mathematical talent and visuospatial processing and a certain advantage for women in terms of writing ability and language use; It should therefore be noted that there are differences between men and women in average values of certain measures, which presumably reflect intelligence.
Intelligence and educational success
The correlation between intelligence and educational success is positive. This correlation can have several explanations, such as: B. smarter people might be on average better educated because of their higher intelligence, or more educated people might be smarter on average because of their higher education. Many scientists assume that education has a positive effect on intelligence in the short term, but that this effect subsides in the long term.
According to a study of over 70,000 English children, the correlation between psychometric intelligence at the age of 11 and educational success in 25 school subjects at the age of 16 is 0.81. This result shows the great positive influence of intelligence on educational success. One study looked at the question of how well educational success and intelligence can predict the extent to which a layperson shares the economic views of the average economist. Based on data from the General Social Survey , it was shown that although both higher education and higher intelligence increase the likelihood that a layperson shares the views of an economist, intelligence is a better predictor than educational success in most areas. One conclusion from these results is that the positive effects of education on intelligence may be smaller than previously expected.
There have been some attempts to increase intelligence through educational programs. Underprivileged children often have low IQs and are the primary target of these programs. In the USA in particular, a large number of programs have been started as part of the Great Society Domestic Agenda , all of which are based on the concept of compensatory education . Examples are the (now discontinued) Milwaukee Project and Head Start , as well as the Abecedarian Early Intervention Project and the High / Scope Perry Preschool Project . In Great Britain , based on the Head Start model, the so-called Early Excellence Center was founded and the Sure Start program launched. The first Early Excellence Center has also been opened in Germany. In general, it can be stated that these programs can increase intelligence in the short term, but the gains tend to disappear again after leaving the program.
A study published in 2012 on the consequences of compulsory schooling, which was extended from 7 to 9 years in Norway in the early 1960s, found that the IQ measured among students at the age of 19 increased by an average of 3.7 points for each additional school year completed.
type of school
In Germany, due to the multi-tiered school system, studies are available on the question of whether, given the same entry requirements, the intelligence performance increases more by attending grammar school than by attending secondary school. The Max Planck Institute for Human Development carried out a study on this (the BIJU). Strong effects could be demonstrated: When the output performance was checked in the intelligence test in class 7, the pupils who attended high school were able to increase their intelligence performance by 11.39 points more than the pupils who attended high school.
In America, a study of 1,450 schools showed a connection between the qualifications of teachers and the IQ of the children they teach. Even after controlling the effects of other factors (such as poverty), being taught by an unskilled teacher was correlated with lower IQ scores.
Threat from stereotypes
A stereotype threat is when a person believes they belong to an underperforming group and therefore fails an IQ test. The phenomenon could be proven for women, for example: Steele let male and female students take part in a test of math skills. Shortly before the test, half of the sample were told that there were usually large gender differences in this test. In fact, women now fared significantly worse than men. The other half of the sample did not receive this notice. No significant gender differences could be shown here. Other groups can also be threatened by stereotypes - such as members of ethnic minorities or members of the lower social classes. Sometimes a stereotype threat can also be demonstrated for entire nations. Harold Stevenson was able to prove that Americans were more threatened by stereotypes than members of Asian nations and therefore performed poorly in tests of mathematical skills.
The project was run by the University of Wisconsin with the aim of researching why a third of all mentally retarded children in Milwaukee were from the same neighborhood in the city that only 3% of the population lived. Furthermore, a solution for this problem should be found.
Children whose mothers had an IQ of 80 or less were selected for the project and then divided into treatment and control groups. The children in the treatment group were brought to a so-called Infant Stimulation Center as babies , where they were individually and intensively cared for by personal trainers, all of whom were graduates from the field of education and psychology. For example, the trainers played educational games with the children or read to them. In addition, the children received an individual menu that was drawn up by a doctor.
At 6 years of age, the children in the treatment group proved to be above average intelligent. They had an average IQ of 120 and there were quite a few gifted people among them. In contrast, the children in the control group had an IQ of 87, and there were no gifted children among them. After that, the care ended.
The children were no longer encouraged and attended the poor public schools in their neighborhood. Their IQ began to drop, so by the age of 14 they had an average IQ of 101. They were thus average intelligent and, above all, significantly more intelligent than the children in the control group.
Head Start is an American program for compensatory education that has been trying to improve the educational opportunities of children from socially disadvantaged families since 1965. Approximately 24 million preschoolers participated in the program by 2007, which has a budget of nearly $ 7 billion.
The program is divided into several sub-projects. Early Head Start looks after the parents-to-be, especially the mothers, during pregnancy and offers various advice and courses. The actual Head Start looks after the children after school, for example by helping them with their homework or visiting exhibitions. With Migrant and Seasonal Head Start , a program for children of migrants and seasonal workers was created.
The effect of the program is controversial. While some studies attest Head Start overall or at least partial success, others criticize the fact that it is not working on the entire problem, i.e. the overall social situation, but only singling out a partial aspect.
The Follow Through Project , with 100,000 participants and a cost of one billion dollars, was the largest study in the world to date with the aim of finding effective methods for teaching disadvantaged children. It was originally planned as a social plan to expand the Head Start program and lasted from 1967 to 1995.
The 22 different models approved by the Department of Education were developed by educationalists from renowned universities. There was only one exception, the direct instruction model from preschool teacher Siegfried Engelmann . The aim of the study was to raise the economically and educationally poorest schools in the USA to the American average.
The follow-through data was evaluated by two independent institutes. The direct instruction model was the only one to achieve positive results close to the American average in all subjects and in terms of self-esteem.
Possibly the Pygmalion effect postulated by Rosenthal and Jacobson can lead to an increase in intelligence up to and including giftedness. It is a kind of self-fulfilling prophecy : the scientists told elementary school teachers that some children in their class had been identified as gifted; but in reality they were chosen at random. Due to the alleged giftedness of the students, the teachers were now increasingly concerned with these students, whereupon strong IQ increases could be determined in the students. Even if the attempts by Rosenthal and Jacobson were criticized, among others by Hans Jürgen Eysenck , who accused the authors of methodological errors , they nevertheless show how important individual support is for the development of intelligence.
Music lessons have a positive impact on IQ if it takes place at a young age. One study found no effect of music lessons on spatial awareness, but an effect on verbal IQ. Significant differences in brain structure were found between musicians and people who did not play an instrument. Some studies suggest that early musical training has positive effects on language and reading skills.
Another study showed a small but significant positive influence of keyboard lessons and singing lessons on IQ. The influence was maintained when parents' income and education were controlled. In a further study in which preschool children received a computer-based cognitive four-week short training session with ten hours per week, a short training session with musical content showed a greater positive effect than a short training session with elements of the performing arts.
One explanation for the effect of music lessons on language competence is postulated that music and language involve the same sensory or cognitive processing mechanisms in the brain, with music making higher demands. At the same time, the music brings an emotional reward and frequent repetition and requires concentrated attention. These factors activate neural plasticity, which leads to long-term changes in the brain and influences language processing.
Drug performance enhancement
Despite the complexity of the human brain, it is now possible to pharmacologically improve sub-factors of the intelligence of healthy adults. The active ingredient methylphenidate, for example, increases the capacity of the spatial working memory and the ability to plan when it comes to unknown tasks. Modafinil, on the other hand, increases pattern recognition and spatial planning performance, and improves short-term memory for numbers. The acetylcholinesterase inhibitor physostigmine improves working memory in facial recognition. The hormone erythropoietin , believed to increase neuroplasticity, increases verbosity one week after a single injection that does not affect blood composition. Finally, the nicotine agonist GTS-21, which is still in the approval phase, also increases the performance of the working memory. Interestingly, the improvements from modafinil and methylphenidate are more pronounced in people with proportionally lower mental performance. The relatively low absolute strength of the effects, the sometimes high costs, the sometimes severe side effects and unresolved neuroethical issues prevent the widespread use of these drugs . Although extensive research is being carried out in the area of increasing intellectual performance, particularly open questions of liability and the lack of legal and social norms inhibit further development.
Intelligence in other disciplines
The neurosciences deal, among other things, with the neural basis of intelligence and the processing of signals and information in humans . The processes in the cerebrum (cf. also cortex ) are particularly relevant for intelligence , whereas the cerebellum (Latin: cerebellum ) and phylogenetically older areas (e.g. the brain stem ) receive less attention in research on the neural basis of intelligence. However, this does not mean that intelligence can be localized in certain areas of the brain.
In computer science, the topic is dealt with in the context of research on artificial intelligence (AI). It describes the replication of human intelligence within computer science . AI is increasingly being used in many areas. Areas of application are e.g. B. optimization problems ( route planner , rail traffic ), dealing with natural language ( speech recognition , machine translation , search engines on the Internet, social bots e.g. cleverbot etc.), dealing with natural signals ( image understanding , image recognition , face recognition , pattern recognition , etc.), humanoid robots (e.g. Atlas , ASIMO , Pepper ), autonomous weapons , etc. AI is also often used in computer games for computer-controlled opponents. (see also applications of artificial intelligence ).
The basics of neural networks in the human brain have been understood. Such networks are simulated in the computer, which simulates the functioning of the human brain (see artificial neural network ). With ever more powerful computers, such artificial networks are becoming more and more efficient. In this way, machines become capable of learning, similar to the brain (see machine learning ). The point at which artificial intelligence outperforms human intelligence is called technological singularity .
The Turing test is a measure of whether a machine can demonstrate an intelligence equivalent to that of humans . If, during this test, a person is no longer able to recognize whether the other person (e.g. during a telephone conversation) is a machine or a person, the machine is considered intelligent in this sub-area. The machines have already passed the Turing test in some defined areas. An AI that you can test yourself online is e.g. B. Cleverbot , which specializes in small talk (see also Comparison of AI with human intelligence ).
What AI has so far lacked is self-confidence or awareness (see also awareness of artificial intelligence ). Artificial intelligences also have so far no emotions (see also emotions of artificial intelligences ).
A system that obviously shows intelligent behavior remains only a tool as long as there is no self-confidence and no motivation to act of "its own" drive and to pursue "own" interests (see also Philosophical Zombie ). A sufficiently intelligent technology, which also crossed this limit and also possibly showed reactions that could be interpreted as emotional, would raise various ethical questions regarding the rights and responsibilities of such a system. Among other things, it should be discussed whether a "biological" intelligence is fundamentally to be assessed differently from a "technological" one.
Transfer to zoology and botany
Due to the ambiguous definition of intelligence, it is difficult to apply the concept to animals. At the same time, however, findings from animal experiments in behavioral research are also interpreted against the background of theories on human intelligence. Therefore, animals and occasionally even plants (see plant intelligence ) are assigned intelligence. Intelligent behavior in animals usually means a cognitive performance that goes beyond instinctive behavior triggered only by key stimuli and reveals a certain assessment of a situation as well as the weighing of alternative courses of action.
Behavioral findings that were interpreted in such a lie, for example, in front of cephalopods (see also Pacific giant squid ), crows and ravens , magpies , monitor lizards , parrots , ants , bees , rhesus monkeys , apes and theropods . The so-called mirror test is also often discussed against the background of the intelligence concept.
Emotional intelligence is one of John D. Mayer ( University of New Hampshire ) and Peter Salovey ( Yale University introduced) in 1990 Terminus . It describes the ability to (correctly) perceive, understand and influence one's own feelings and those of others. The concept of emotional intelligence is based on the theory of multiple intelligences by Howard Gardner , the core idea of which was already referred to by Edward Lee Thorndike and David Wechsler as " social intelligence ". Thorndike made this clear as early as 1920 with an example according to which the (technically) best mechanic will fail as a foreman if he lacks social intelligence. The topic of "emotional intelligence" is thus also a contribution to the discussion of the question of success in life and at work.
Social intelligence is a complex of skills that serve to take control of reality and to act effectively in communication and interaction situations according to the needs of those involved. Action can be described as effective if it allows positive (desired) consequences to be maximized and negative (undesired) consequences to be minimized. The multitude of definitions can be differentiated according to whether they describe social competence as a uniform construct (molar) or as a combination of several socially relevant behavioral patterns (molecular).
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