Genes and Behaviours

Question 1

What is the aim of Bouchard and McGue’s 1981 study?

Answer 1

To investigate IQ correlations between siblings. They did this to answer the question of whether intelligence is determined by nature or nurture.

Question 2

Procedure of Bouchard and McGue’s study in Ohio.

Answer 2

In Ohio, they tested on 121 monozygotic twins and 171 dizygotic twins that were being enrolled in kindergarten or finishing first grade, with the average age being 6.07.
They used a shorter version of the Stanford-Binet IQ test which includes the areas of vocabulary, pattern analysis, memory for sentences, memory for digits, and quantitative “subtests”. All of these subtests were put together using a “g” score which measured general cognitive ability.

Question 3

Procedure of Bouchard and McGue’s study in UK.

Answer 3

In the UK, they used a sample of twins born between the years of 1994 and 1996. The average age was 11.57.
They tested the zygosity (genetic similarity) of twins by a parent questionnaire of physical similarity.
The twins, when at age 12, were asked to take tests: 2 verbal tests, a “Multiple Choice Information” test and “Vocabulary Multiple Choice subtests”: and 2 non-verbal tests, the “WISC-IIIUK Picture Completion” and the “Raven’s Standard and Advanced Progressive Matrices”.
This provided data for 1518 MZ twins and 2500 DZ twins.

Question 4

Procedure of Bouchard and McGue’s study in Australia.

Answer 4

In Australia, they pulled 338 MZ twins and 513 DZ twins recruited through schools, the average age was 16.
Zygosity was determined through 9 specific DNA markers, cross checked with blood testing and phenotypic data.
Overall zygosity accuracy was higher than 99.9%.
There was a parental report of a significant head injury, history of substance abuse or taking medications with severe central nervous system impact.
They gained written consent from the twins and the twins’ parents/guardians to conduct the experiment.
The twins were then tested as closely as possible to their 16th birthday on 3 verbal and 2 performance subtests.

Question 5

Findings of Bouchard and McGue’s study?

Answer 5

Results indicated a significant effect due to gender on 4 out of 6 samples, with males doing better than girls.
Found that there was a positive correlation between kinship and IQ correlation.
The closer the siblings were, the more similar their IQ.

Question 6

Conclusions of Bouchard and McGue’s study?

Answer 6

Supports the nature part of the debate

Question 7

Strengths of Bouchard and McGue’s study?

Answer 7

Large study as sample was reasonably representative of the population’s ethnicity, employment status and parental education, so generalisable.
This study focused on the intellectual abilities of people, not their artistic or athletic abilities, which isn’t needed in achieving its aim.

Question 8

Limitations of Bouchard and McGue’s study?

Answer 8

However, siblings are raised in the same environment, so influence may not be purely genetic. This makes it difficult to differentiate between the influence of genetics and environment.
Also, age- the further apart the siblings in age, the less correlated their IQs are expected to be.