The statistical synthesis of the data from a set of comparable studies of a problem that yields a quantitative summary of the pooled results.
Minnesota Twin Study
(Bouchard et al. 1990) A longitudinal study that has been going on since 1979 in which identical twins raised apart (MZAs) are compared to identical twins raised together (MZTs).
Less Effort Hypothesis
Those with higher IQs use less energy to think that those with lower IQs.

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IQ - tests which can indicate one's genetically endowed intellectual potential
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Alfred Binet (pioneer in intelligence research at the beginning of the 20th century)
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- developed an intelligence tests
- improve French education system

Main controversies regarding intelligence
inherited / result of environmental stimuli

1) Poverty has an influence on the development of the child's intelligence.
2) (1994) Harvard professor, Richard J. Herrnstein - Published The Bell Curve :
- debate about genes/environment influences on ethnic differences remains unresolved

Nature of intelligence :
- What is it?
- How can it be measured?

Charles Spearman
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- early intelligence theorist
- found that students performance across different subjects was positively correlated
- general intelligence factor : basis of all intelligence = "g" factor

Modern Intelligence Tests :

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- assess "g" factor

- not looking at specific school subjects

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Where does "g" come from?


Bouchard and McGue (1981)
- 111 studies of IQ correlations
- sample: siblings from around the world
- meta-analysis
- results: closer kinship = higher correlation of IQ

Role of Genetics in Intelligence:
- research on identical twins
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- 100% percent genetic relationship
- brought up separately from birth
- grown up in different environments
... any similarity between their IQs = due to genetics rather than enviornment

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Minnesota Twin Study

- Bouchard et al. 1990
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- longitudinal study since 1979
- Identical twins raised apart (MZAs) compared to identical twins raised together (MZTs)
- most cross-cultural study
- sample: all over the world
- mean age : 41 years old (at the start of the study)
- almost all research on adolescents
- procedure: about 50 hours of testing and interviews
Concordance rate of intelligence from study
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Same person tested twice
Identical twins reared together
Identical twins reared apart
Fraternal twins reared togher
Biological siblings reared together
- heritability of about 70%
= 70% of intelligence can be from genetic inheritance
= 30% of intelligence may be from other factors

Criticisms of the Minnesota Twin Study
- Bouchard relied on media coverage to recruit participants
- There are some ethical concerns about the way he reunited the twins
- There was no adequate control to establish the frequency of contact between the wins prior to the study
- We cannot assume that twins who are raised together experience the same enviornment = "equal enviornment assumption"

Adoption Studies
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- intelligence of the adopted child is correlated with the intelligence of the adoptive parent
- no biological link
= environmental influences should be evident

Scarr and Weinberg (1977) and Horn et al. (1979)
- parents who raised both adopted and natural children
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Assumption: all children had the same upbringing + same enviornment + same parents
- findings: no significant difference in IQ correlation
- Most of the sample: parents were wealthy, white, and middle class, with high IQs - adopted children were poor, low-class backgrounds, with lower IQ parents

Wahlstein (1997)
- well-controlled adoption studies in France
- findings: transferring an infant from a low socio-economic status family to a home with high socio-economic status parents = improves childhood IQ by 12-16 points
... intelligence has a lot to do with the enviornment + genetics
= enriched environment may raise the IQ of children

CONCLUDING THOUGHTS ON INTELLIGENCEWhat is intelligence?Is it only based on knowledge?Or is it related to our ability to solve problems?Hainer et al. (1988)- PET scan studyexternal image pet_scan.gifWhen solving a reasoning problem: individuals with a high IQ : lower metabolic rateindividuals with lower IQ : higher metabolic rate- only seen in problem solving- not in data recall= higher IQ's use less energy to think = less effort hypothesisPlomin and Petrill (1997)external image RobertPlomin.jpg- correlation between parent and child IQs change over time- 4 to 6 years = 40% correlation- early adulthood = 60%- older adults = 80%... genetic disposition pushes us towards environments that accentuate that disposition... increased heritability throughout the lifespan- Socio-economic class = one of the most important environmental factors: development of intelligence- Poverty (not genetic inferiority) - key to understanding differences in intelligenceFlynn effect- rise of average scores on intelligence tests- most parts of the world- in the last centuryJames R. Flynn - document this to create awareness of its implicationsexternal image flynn.jpgexternal image 9780521880077.jpgUlric Neisser - article in The American Scientist (1997) external image 08357782540388858.jpg- average mean scores on IQ tests are increasing by about 3 points every 10 years

- higher increase in abstract-reasoning ability
- cause: unknown
... possibly:
- real increase in intelligence
- increasing ability to crack intelligence tests
- better nutrition
- improved schooling
- different child-rearing practices
- increased use of technology in modern life
Neisser : living in a highly visual environment may play an important role in the rise of IQ scores.

Short Answer Question
Explain How Research on Intelligence Helps the Study of the Influences of Genetic and Environmental Factors

Core - Biological Level of Analysis
Biological Level of Analysis - Genetics and Behavior