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Intelligence (Van Leeuwen et al (Background: suggests MZ twins can…
Intelligence
Types of intelligence
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Gardner's eight intelligences: suggested we all possess these intelligences, just in smaller and greater amounts, for example having high interpersonal intelligence, but little musical intelligence
Intelligence can be defined as understanding complex ideas, adapting effectively to an environment and to learn from experience
Spearman initially suggested the term general intelligence- he studied that people who perform well on one kind of cognitive test tend to perform well on others too. He labelled this with the symbol 'g'. He also labelled 's' which defined more specific intelligence, such as in maths.
Biological factors
Genes
Twin studies: allows to compare for differences in intelligence for MZ (100% same genes) and DZ twins (50% same genes). McGue found a variation in concordance rates for IQ scores, +0.86 for MZ and +0.60 for DZ.
Adoption Studies: useful in comparing twins raised together and twins raised separately. McGue found MZ twins raised apart had greater intelligence concordance rates (+0.72) than DZ twins raised together (+0.60)- significant influence of heritability compared to the role of the environment.
Brain Structure
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Areas of the Brain: intelligence may be correlated with larger volume in the prefrontal cortex and Broca's area.
Grey Matter: larger volumes of grey and white matter that help process information could be linked with higher intelligence
Nutrition
Effective neurotransmitter function depends on the presence of certain chemicals in the diet- the absence of certain nutrients have been linked with lower intelligence
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Van Leeuwen et al
Background: suggests MZ twins can identify genetic influence on a intelligence when the similarity is greater than in DZ twins. Assumptions- parents have different levels of intelligence (phenotypic assortment or social homogamy are not influenced) and genotypes and environment are not correlated.
Aims: to extent on twin studies by using parents and siblings to test whether biological factors (genotype) or psychological factors (phenotype) affect intelligence more.
Method: a twin-family design was used with 112 Dutch families, including a pair of twins (48 MZ and 64 DZ with a mean age of 9) and an older sibling with a mean age of 12. Researchers were investigating the IQ's of families.
Procedure: the children and parents were tested on either the Raven's Standard progressive matrices or the advances version which provided a score of general intelligence (g). MZ twins were also tested to ensure zygosity through cheek swabs and genetic testing. This was standardised.
Results: phenotypic assortment- 58% of IQ variation was due to genetic variation and 42% was due to unshared environmental variation.
Social homogamy- 15% IQ variation due to genetic variation, 19% dominance variation, 27% shared environmental variation and 39% unshared.
There was a 67% heritability (genetic effects) score for IQ.
Conclusions: the model assuming phenotypic assortment was superior- intelligence is best explained through additive (directly passed) genetic effects, rather than environmental factors. This research put greater emphasis on the influence of genes compared to previous research- however this research is consistent with Spearman's view that general intelligence is mostly inherited