Aim?
to separate the genetic and environmental effects on IQ and to also investigate why spouses have similar intelligence scores
Sample?
Twins recruited from the Netherlands twin registry, and twin families with an extra sibling aged 9-14 were also collected.
112 families participated in the study, with 103 having full siblings participating.
Procedure?
The procedure started by collecting cognitive behaviour and hormonal data, pubertal status and MRI brain data on two different days, as well as cheek swabs for DNA collected at home.
Children were tested for cognitive ability in separate rooms with a cognitive test battery with the Raven’s standard progression matrices. The parents used Raven’s advanced progressive matrices and the whole procedure lasted 5 hours.
Findings?
There was no significant sex difference observed however the correlations were higher in monozygotic twins than the other relatives. The mean IQ score was higher in older siblings and there was also more variance in siblings than twins. The environment was more important in explaining individual differences for low IQ groups than high IQ groups.
Conclusions
he study concluded that individual differences were largely accounted for by genetic differences (67%), and parental influence on children’s IQ is explained by gene transmission not cultural transmission. The study also concluded that environmental factors were more important in children who were genetically predisposed for low IQ.
How does it explain the effects of biological factors upon intelligence?
- study suggests that biological factors have the most influence.
- Consider that genetics simply give a child the predisposition for intelligence - not definitive measure
- Reductionist view
- even with twin studies, impossible to tell whether genetics or environment effects intelligence
Methodological issues?
- cultural bias - cannot find standardised test
- Unrepresentative sample - ethnocentric
+ Limits extraneous variables -
Assess the use of IQ tests in job applicants
- IQ tests create stigmas
- Multiple intelligence - doesn’t label so more socially sensitive-not very accurate due to self report
- standard IQ may be best - standardised and little opportunity for external factors to have an effect.
