Van Leeuwen (Topic 1 child twin-family general IQ (intelligence) Flashcards
Background
Previous twin studies estimated contribution of genetic effects to variability in intelligence at 25% to 50%.
Part of remaining variance due to environmental factors shared by children who grow up in same family (Bartels et al 2002)
(Finley and Perderson 2001) found environment has greater influence on less intelligent people than more intelligent.
Study uses extended twin design including MZ & DZ twins, their siblings and parents.
Aim
Aims to build on earlier research.
Investigated whether biological factors and/or environmental might affect intelligence.
Hypothesis
Van Leeuwen predicted genetic effects would explain large part of any individual differences in intelligence.
Genetic transmission
Transfer of genetic info from genes to another generation.
Cultural transmission
The way a group of people within a society or culture tend to learn and pass on info.
Assortative mating
Individuals with similar genes or observable characteristics mate with one another more frequently than those who do not.
Gene- environment interaction
Theory that certain environments ‘activate’ a particular gene.
Gene-environment correlation
Parents transmit their genes and their environment to their children.
e.g parents may be predisposed to good health and fitness, but also share this lifestyle to their children therefore makes it difficult to establish contribution of nature/nurture.
Heritability
Extent to a parents genes are responsible for a phenotype (way genes are expressed through physical, behavioural and psychological characteristics; determined by both genes and environment)
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 same environment and more likely to end up having children together.
Research method
Research article/paper.
Assesses presence of assortative mating gene-environment interaction and correlation & the heritability of intelligence in childhood.
Twin- family design with twins, their siblings and parents from 112 families.
Also viewed as collection of (mini) case studies, the findings of which were collated and analysed to compare 2 hypotheses about cause of assortative mating in intelligence.
Also viewed as correlational study as researchers were looking for relationships between such factors as intelligence and biological factors, intelligence and environmental factors.
Sample
Twins recruited from Netherlands Twin Registry (NTR) at VU University in Amsterdam.
112 twin families with extra sibling between 9 - 14 yrs old agreed to take part.
Families with children with major medical history were excluded.
Mean age of twins at time of cognitive assessment was 9.1 yrs.
Sample made up of 23 MZ male, 23 DZ male, 25 MZ female, 21 DZ and 20 DZ pairs of opposite sex.
Mean age of siblings was 12 yrs.
Mean age of biological fathers and mothers were early 40s.
Monozygotic twins
Identical
Dizygotic twins
non-identical
Procedure
Parents signed informed consent for children and themselves.
Children also signed own consent forms.
Parents were compensated for travel expenses and children received a present.
Testing procedures
Data collection took place on 2 different days.
Cheek swabs for DNA were collected at home by parents & children prior to intelligence testing to determine whether children were identical or non-identical twins.
For cognitive/intelligence testing, in lab children were tested in separate rooms with Ravens Standard Progressive Matrices (RSPM) and Ravens Advanced Progressive Matrices (APM) for adults.
Whole protocol took approx 5 hours including 2 short breaks and 1 longer lunch break.
In data analysis researchers used 2 different theoretical models to determine whether spousal resemblance is better explained by phenotypic assortment or social homogamy.
RSPM
Consists of 60 problems divided into 5 sets of 12, progressively more difficult
Provides index of general intelligence.
Advanced compared to Standard progressive matrices
Main difference being level of difficulty and includes 12 practice and 36 test items increasing in difficulty more steadily and becoming considerable more complex.
Results
Raven progressive matrices test was used to assess general intelligence (IQ) and persons IQ was estimated using Rasch model- scored converted using this model as it accounts for level of difficulty in questions.
Scores were not solely calculated on amount of correct answers, more difficult q’s have more marks.
Results- gender differences
No significant differences in IQ scores between males and females across all groups (parents, siblings and twins)
Results- variance in siblings
Variance (spread) in siblings significantly larger than in the twins meaning siblings had wide ranging scores on test whereas twins had similar scores
(supports genetic explanation because the more genetic makeup shared, more similar their IQ)
Results- cultural/ environmental factors
Because most of findings supported genetic explanations for IQ level, cultural / environmental factors were therefore NOT significant on their effects on IQ level.
Results- correlations between Raven test scores
Correlations between scores were higher for identical (MZ) twins than siblings and non-identical (DZ) twins- suggesting intelligence is inherited (supports genetic explanation).
Results- genetic effects on intelligence
Genetic effects account for 67% of intelligence (was 25-50% in previous research so this study in INCREASED the figure) remainder is explained by random environmental factors; environment is relatively more important in explaining individual differences for LOW IQ groups.
(Intelligence is mostly genetic, but not entirely (67%) )
Results- correlation between Raven scores parents
Higher correlation between Ravens advanced progressive matrices (adults) between parents.
i.e if one parents had high score, so did the other- provides evidence for assortative mating (phenotypic assortment) suggesting individuals seek partners with similar intelligence levels.
Results- children born with naturally higher/ lower IQ
Those born with low IQ can be affected more by environmental factors compared to those born with high IQs providing evidence for genotype-environment interaction (theory that certain environments ‘activate’ particular gene)
Conclusions
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 significant influence on IQ level (way group of people in a society/culture tend to learn and pass on info).
‘Phenotypic assortment’ (individuals choose one another due to similar intelligence levels) BETTER explains spousal resemblance than ‘social homogamy’ (ppl with similar intelligence levels are clustered together in same environment- more likely to end up having children together).
Methodological issues
Social sensitivity- studying intelligence sensitive suggesting men more intelligent than women.
Twin studies have shown intelligence hereditary= highly deterministic, may create issues in educational system, creates idea certain individuals have thresholds and can only reach certain potential-not positive outlook on one’s intelligence.
Gould’s research suggested differences in intelligence in races/nationalities-had bad consequences in political decisions.
RPM intelligence tests and DNA tests reliable and objective.
All ps completed study individually reducing chance of extraneous variables.
Methodological issues validity of tests
Validity of intelligence tests questioned, Leeuwen concluded from their results main influence on IQ levels is genetic, environment has more effects on lower IQ and no indication intelligent parents provide stimulating environments to promote their children’s intelligence.
RPM measures fluid intelligence (assesses individuals ability to think on the spot & reason about new situations) would be difficult to prepare for such test, thus score determined by their innate cognitive ability.
Leeuwen may have found diff results if other IQ test was used.
On other tests that measure crystallised intelligence (rely on linguistic ability or cumulative knowledge, individuals have control over outcome)
Revision or external environmental influences can improve performance on these types of tests.
Validity of a tests conclusions is affected by type of test used.
Ethical issues
To ensure ethical responsibility, research addressed many potential issues;
Ps volunteered and informed consent obtained from both parents and children.
Ps did not experience stress/distress whilst taking part in tasks.
All tested separately, could take as long as needed to complete IQ test, means ps did not feel pressured to complete test in certain amount of time, nor feel embarrassed if others finished before them.
Usefulness
Seen as useful- helps determine how both nature and nurture interact to influence IQ intelligence.
May not be useful as sample population not representative, although genetic research tends to have large samples, do tend to under-represent ethnic minorities and low-income families.
RPM and intelligence tests can be seen useful as may help identify and categorise individuals in job roles, educational systems, medical support systems.
If psychologists can determine factors that may increase of inhibit persons IQ, practical applications can be developed to help improve it. e.g exposing genetically predisposed to low IQ people to intellectually stimulating environments to raise their IQ.
Sample
Unrepresentative 112 twin families on twin register from Netherlands.
There are multitudes of other twin families in other countries with diff ethnic origins, cultures and environmental and genetic influences, therefore results from this sample- about relative intelligence and contributions of shared genetic & environmental influences in IQ variance-cannot be confidently generalised to other populations, sample lacks population validity.
Further research required to determine which more important in affecting intelligence- genetic or environmental
Nature vs nurture
Provides support for heritability of intelligence= Nature.
67% of intelligence found to be due to genetics & parental influence due to genes.
Conclude genetics have larger influence than environmental factors- but they play smaller role, those with lower IQ more influences by nurture.
Yerkes- created culturally biased test, although attributed intelligence to race/nationality (nature) we see from Gould’s review that it was NOT accurate measure of intelligence.
RPM enabled reduction of cultural bias.
Flynn (1987) points out there is scope for intelligence scores to improve over time suggesting environmental influences (nurture).
Intelligence tests will always be questioned on its ability to measure innate intelligence(nature) in fact intelligence in general.
Free will vs determinism
May appear solely deterministic as it assumes intelligence mainly genetic determined.
Also found spousal resemblance likely product of phenotype assortment-partners choose one another because have similar IQ’s, implying involvement of free will in how we select mates.
Measures of intelligence may support deterministic side as tests like RPM assess ability to think on spot & reason about new situations, therefore difficult to prepare / revise for, likely to measure innate intelligence instead of nurture.
On tests relying on linguistic ability individuals have more choice by freely opting to study to improve performance.
Reductionism vs holism
Assuming intelligence is outcome of a solitary gene is simplistic & reductionist.
Leeuwen made start on more holistic explanation by providing insight into complex intersection between DNA, phenotypes and environmental factors.
Using single tool to assess intelligence always reductionist.
Combination of tests help create more complex thus holistic understanding of individuals intelligence.
