Child Psychology: Intelligence (Biological) Van Leeuwen et al (2008)

Memory Strategy – Child Psychology – Intelligence:

  • Scarr – scarred with your parents intelligence
  • Schoenthaler – diet improves IQ
  • Leeuwen – Look alikes
  • Broca – Brain size
  • Glover – stresses you out
  • Haier – Gender stereotyped brain areas
  • Gould/Yerkes – Racist assessment of intelligence
  • Raven – Used in Leeuwen
  • Goodenough- Harris Drawing

Biological explanations of Intelligence:

Smart Students Learn BGetting Good Healthy Respectable Genes

What psychologists mean by intelligence:

Charles Spearman (1904)– The same Spearman who developed Spearman’s Rho, studied rleationships between cognitive factors in school children. He observed a consistent correlation between a number of academic subjects. Because of this relationship, Spearman propsed that mental ability could be understood as a single general factor, commonly known as the ‘g factor’. According to Spearman half of your intelligence could be explained by the g factor i.e. General cognitive ability, the rest of it would be attributed to motivation or environmental influences such as having a supportive teacher.

Howard Gardener’s 8 intelligence’s:

This theory suggests that traditional psychometric views of intelligence are too limited. Gardner first outlined his theory in his 1983 book “Frames of Mind: The Theory of Multiple Intelligences,” where he suggested that all people have different kinds of “intelligences.” Gardner proposed that there are eight intelligence’s, and has suggested the possible addition of a ninth known as “existentialist intelligence.”

While a person might be particularly strong in a specific area, such as musical intelligence, he or she most likely possesses a range of abilities. For example, an individual might be strong in verbal, musical, and naturalistic intelligence.


Biological factors that effect intelligence:

Individual gender differences:

Broca (1800’s) suggested that head size was a key indicator of intelligence. The bigger the head, the larger the brain, the more intelligent you were. This lead to the idea that males were more intelligent than women because males had larger brains than females. However, further research with more technical equipment has found a small correlation between brain size and intelligence. This is definitely not a causal link.

Haier (2005): Research has found that males have more neuron efficiency during spatial tasks. This has been found because males have more volume of grey matter in the frontal parietal lobe. Whereas females have more neuron efficiency in tasks requiring verbal skills this is evidenced by having more white and grey matter in the Broca’s area (associated with language).

Genetic transference:

Scarr (1978) – Compared the intellectual abilities of parents and their adopted and biological children. They found stronger correlations between biological relatives than between adopted relatives. This implies that genetic factors play a larger role in intelligence.

Nutrition and pregnancy:

Schoenthaler (1991) found that children who lacked nutritious diet in the first place, were able to improve their IQ scores by taking daily vitamin and mineral supplements. However, these children only improved in non-verbal tests, and did not improve in verbal tests.

Goldschmidt (2008) found that heavy cannabis use (one or more cigarettes a day) during the first 3 months of pregnancy was linked to lower verbal reasoning when the child was measured at 6 years old. Heavy use during the second 3 months had effects on memory skills, and heavy use in the last 3 months was associated with low scores on IQ tests.

Glover (2009) studied 250 women during pregnancy and got them to complete anxiety questionnaires and they took blood samples to measure cortisol (stress hormone). The children exposed to high levels of cortisol tended to have lower IQ, especially on verbal and linguistic tests.

Key research: A twin-family study of general IQ Van Leeuwen, M., Van den Berg, S. M. & Boomsma, D. (2008)

Key terms:

  • Genetic transmission: transfer of genetic information from genes to another generation.
  • Cultural transmission: is the way a group of people within a society or culture tend to learn and pass on information.
  • Assortative mating: individuals with similar genes or observable characteristics mate with one another more frequently than those who do not
  • Gene–environment interaction: the theory that certain environments ‘activate’ a particular gene
  • Gene-environment correlation: parents transmit their genes and their environment to their children. For example parents maybe predisposed to good health and fitness, but also share this lifestyle to their children. Therefore it makes it difficult to establish the contribution of nature or nurture.
  • Heritability: the extent to a parents genes are responsible for a phenotype
  • Phenotypic assortment: assortative mating occurs because individuals choose one another because they have similar intelligence levels.
  • Social homogamy: people with similar intelligence levels are clustered together in the same environment they are more likely to end up having children together.

Research Method:

  • This is a research article/paper which assesses the presence of assortative mating gene–environment interaction and correlation and the heritability of intelligence in childhood using a twin family design with twins, their siblings and parents from 112 families.
  • This study could also be viewed as a collection of (mini) case studies, the findings of which were collated and analysed in order to compare the two hypotheses about the cause of assortative mating in intelligence.
  • In addition, the study may be viewed as a correlational study as the researchers were looking for relationships between such factors as intelligence and biological factors, intelligence and environmental factors.


  • Twins were recruited from the Netherlands Twin Registry (NTR) at (VU) university in Amsterdam.
  • Twin families with an extra sibling between 9 and 14 years were selected from two birth cohorts (1995–1996). Families with children with a major medical history  were excluded.
  • Of the 112 families, 103 had full siblings who wanted to participate.
  • Mean age of the twins at time of cognitive assessment was 9 years
  • Mean age of the siblings was around 12 years
  • The mean age of the biological fathers and mothers were early 40’s


  • Parents signed informed consent forms for their children and themselves. Children also signed their own consent forms. Parents were compensated for their travel expenses and children received a present.

Testing procedures

  • Data collection took place on two different days.
  • Cheek swabs, for DNA, were collected at home by parents and children prior to the intelligence testing to determine whether the children were identical twins or non-identical twins.
  • For cognitive/intelligence testing, families arrived in the morning. Children were tested in separate rooms with a Raven’s Standard Progressive Matrices (RSPM) test. They were given verbal instructions and completed the test at their own pace. The test consisted of 60 problems in 5 sets of 12 problems that became increasingly difficult as the test progressed. The test covers a range of cognitive abilities, from identifying missing puzzle pieces to completing analogies. The RSPM is a non-verbal ‘culture fair’ multiple choice IQ test, that measures your fluid intelligence (the ability to reason and solve problems using new information without relying on previously acquired knowledge and skills. The ability to deal with novelty, to adapt one’s thinking ‘fluidly’ to a new, unfamiliar problem.
  • Crystallized intelligence is defined as the ability to use learned knowledge and experience
  • Parents completed the Raven Advanced Progressive Matrices (RAPM) which is made more difficult to suit adults. Reported retest reliability for adults is 0.91. 
  • Parents received the RAPM (maximum achievable score = 36), offspring received the RSPM (maximum achievable score = 60)
  • The whole protocol took approximately 5 hours, including two short breaks and one longer lunch break.

Use the link below to see some examples of the progressive measures questions.

  • In their analysis of the data, researchers used two different theoretical models to determine whether spousal resemblance is better explained by phenotypic assortment or social homogamy.


The Raven Progressive Matrices test was used to assess general intelligence (IQ) and a persons IQ was estimated using a Rasch model. The reason why the scores were converted using the Rasch model is because this model accounts for the level of difficulty in the questions. Therefore, scores were not solely calculated on amount of correct answers. Questions that were more difficult, have higher weightings.

  • There were no significant differences in IQ scores between males and females across all groups (parents, siblings and twins)
  • The variance in the siblings was significantly larger than in the twins. This means that siblings had wide ranging scores on the test, whereas twins had very similar scores. Again this supports a genetic explanation, because the more genetic makeup the share, the more similar their IQ is.
  • Because most of the findings supported genetic explanations for IQ level, cultural/environmental factors were therefore not significant on their effects on IQ level.
  • Correlations between Raven test scores were higher for identical twins, than siblings, and non-identical twins. Again suggesting that intelligence is inherited.
  • There was a higher correlation between the Raven IQ test scores between parents i.e. if one parent had a high score, so did the other. This provides evidence for the assortative mating (phenotypic asssortment), as it suggests that individuals seek partners with similar intelligence levels.
  • Children who are born with low IQ’s can be effected more so by environmental factors compared to children who are born with high IQ’s. Therefore providing evidence for genotype-environment interaction.


  • The main influence on IQ level is genetic factors, however genes do interact with environmental factors to influence intelligence in significant ways.
  • Cultural transmission does not have a significant influence on IQ level.
  • Phenotypic assortment better explains spousal resemblance that social homogamy.

Debates related to Leeuwen – intelligence:

Methodological and ethical issues:
Studying intelligence can be socially sensitive, especially when research has suggested that men are more intelligent than women. Twin studies which have shown intelligence to be hereditary is highly deterministic and may create issues in the educational system, creating this idea that certain individuals have thresholds and can only reach a certain potential. This doesn’t impose a positive outlook on individuals intelligence. Research by Gould also suggested differences in intelligence when it comes to race and nationality and this had horrendous consequences in political decisions.
Leeuwen (2009) followed ethics such as gaining consent form parents and children before participating in the study. However, although a large sample, it is only twin families that are included and therefore can out by generalised to the wider population i.e. Non-twin families.
The RPM intelligence tests and the DNA tests can be said to be reliable and objective. In addition all participants completed the study individually, reducing the chance of extraneous variables.
Usefulness of research:
Leeuwen can be seen as useful as it helps to determine how both nature and nurture interact to influence IQ intelligence. However, it may not be useful as the sample population are not representative. Although genetic research tends to have large samples they do tend to under-represent ethnic minorities and low income families. RPM and intelligence tests can be seen as useful as it may help to identify and categorise individuals in job roles, educational systems, medical support systems.
Nature vs nurture:
Leeuwen provides support for the heritability of intelligence. Although they do conclude that genetics have a larger influence, they admit that environmental factors do play a smaller role. Yerkes created culturally biased test and although he attributed intelligence to nationality and race (nature) it became clear from Goulds review that it was not an accurate measurement of intelligence. Ravens Progressive Matrices enabled the reduction of cultural bias. Flynn (1987) points out that there is scope for intelligence scores to improve over time, therefore suggesting environmental influences. Intelligence tests will always be questioned on its ability to measure innate intelligence, in fact intelligence in general.
Freewill vs determinism:
Leeuwen although may appear solely deterministic due to its assumption that intelligence is mainly determined by genetics. They also found that spousal resemblance was a likely product of phenotype assortment. In other words, partners choose one another because they have similar IQ’s, implying the involvement of freewill in how we select mates.
Measures of intelligence may also support the deterministic debate as tests such as RPM assess ones ability to think on the spot and reason about new situations. Therefore it is difficult to prepare or revise such tests and would therefore be likely to measure innate intelligence. On tests that rely on skills such as linguistic ability, individuals have more choice by freely opting to study in order to improve their performance.
Reductionism vs holism:
Assuming that intelligence is the outcome of a solitary gene is a very simplistic and reductionist explanation. Leeuwen made a start on a more holistic explanation by providing an insight into the complex intersection between, DNA, phenotypes and environmental factors. Using a single tool to assess intelligence will always be reductionist. Where as using a combination of intelligence tests help to create a more complex and thus holistic understanding of an individuals intelligence.

Applications: Methods of assessing intelligence

The IQ Test:

The IQ test comprises of a number of questions that may relate to knowledge and language skills. IQ tests can be used to assess achievement, diagnose problems, or to identify aptitude or potential.

The Raven’s Progressive Matrices:

The teacher could use a Raven’s Progressive Matrices which is a test that is the most popular to measure non-verbal intelligence. It aims to measure educative reasoning i.e. the ability to infer or work out an answer based only on the information they have been given. The test provides pictures that the students have to make meaningful. So for each test item the students have to select a missing aspect in a series of stimuli in order to complete a pattern. The items on the test get progressively more challenging as the test goes on. This also means that a point for an easy questions doesn’t have the same weight as a point awarded for a difficult question. The Raven Progressive Matrices use a specific calculation to interpret the results more accurately. The Raven’s Progressive Matrices now comes in three different versions:

Colour Progressive Matrices: For children between 4-7 years old and individuals with mental or physical disabilities – around 36 items assessing colour and some black and white items.

Standard Progressive Matrices – young people and children and Advanced Progressive Matrices – adults. These tests were used in the Leeuwen study.

Application of the RPM: This measure tends to be used with children or individuals with language or learning difficulties as it doesn’t rely and language or written ability. The RPM is used across the world and has many different purposes. For example RPM has been used as an entry exam into the military. In addition, due to the nature of the test items means that all versions of the test are comparable, meaning that test scores from the Standard RPM taken by children can be meaningfully compared with adults who have completed the Advanced RPM.

Goodenough-Harris Drawing Test:

This tests asks students to to draw a man, a woman and the child – him or herself. Analysis of the features of the drawings such as absence of the details and the proportion of features such as hands and fingers can give an intelligence estimation.


Evaluation of using intelligence tests:


  • The main strength of IQ tests is the ability to provide a rough estimate of the raw intellectual ability of a test taker. The results of tests can be used to estimate future performance of test takers.
  • The IQ test is highly standardised Intelligence. If the IQ test is standardised on a group of people and then, to ensure validity, should only be used on people in that group.
  • The IQ test can be used to highlight individuals who may be at risk and therefore, individualised support networks can be put in place to help develop their intelligence.
  • It can also be used to identify gifted individuals so that they can be challenged in order to further their potential.


  • IQ tests are limited in scope and therefore are not always good predictors of academic or job performance.
  • Another weakness of IQ tests is that designing a test to interpret intelligence presumes that intelligence can be adequately defined and tested by using a simple paper-and-pencil, multiple choice exam. IQ tests often contain logical word problems or problems involving shapes and numbers, but such problems may not necessarily form an accurate picture of intelligence. For instance, a person with a very high IQ score may have no talent for music, while another person with an average IQ score may be musically gifted.
  • Another failing of IQ tests is the inability to evaluate characteristics that are important to achievement in the world that may not be directly related to IQ scores. For instance, the ability to interact well with others is an essential skill that many consider to be a form of intelligence, but this is not measured by IQ tests. Other important personal characteristics such as motivation to succeed, disposition and self-discipline are also not measured by IQ tests.
  • Perhaps the most important qualities in terms of employment opportunities are skills and knowledge. Skills and knowledge are learned through study and practice, but these qualities are not tested by IQ tests. Someone can have a genius level IQ but have little actual knowledge or skill, while another person with an average IQ may have spent years educating herself to obtain practical skills and knowledge.
  • Another issue is that not all IQ tests are the same and difficulty may vary, meaning that a certain score on one test may not be equivalent to the same score on another.