Turkheimer . 2003. Socioeconomic Status Modifies Heritability of IQ in Young Children. Background : Previous research, such as the Minnesota Twin Studies, has shown that identical twins are much more similar in levels of intelligence than fraternal twins.
Previous research, such as the Minnesota Twin Studies, has shown that identical twins are much more similar in levels of intelligence than fraternal twins.
This indicates that intelligence is highly heritable, it runs in families.
Environment has been viewed as less important, except in the most extreme cases.
However, most of the twins on which this research has been based have come from, or been raised in, affluent families.
It has not been certain that the same heritability of IQ exists in poorer families.
To investigate the role of the environment, and in particular whether heritability of intelligence is equally high in all socio-economic classes.
Turkheimersearched for data on twins from a wider range of families than had previously been included.
In a sample from the 1970’s he found 320 twin pairs, many from poor families, who had taken IQ tests at age 7.
Turkheimerperformed correlational analysis on the twins data to examine whether identical twins had more similar IQs than fraternal twins.
Heritability of IQ among the twins who had grown up in affluent families was, as expected, very high (about 0.6).
The big surprise is among the poorest families. For the children who grew up poor, the IQ’s of identical twins vary just as much as the IQ’s of fraternal twins, meaning that heritability of IQ is close to 0.
Conclusion and Interpretation:
The impact of growing up impoverished outweighs any genetic influences on IQ, so that differences in IQ between children in poor families can best be attributed to differences in these children’s environments, not their genes. “If you have a chaotic environment, kids’ genetic potential doesn’t have a chance to be expressed,” Turkheimer explains. Meanwhile, in affluent families, differences between children’s IQ can to a large extent be explained in terms of genetics.
Read in the CC page 53-56. Now, how can Turkheimer’s results be evaluated?
How should Bouchard be evaulated?
Put also to memory: Scarr and Weinberg (1977), Wahlsten (1997), Plomin and Petrill (1997).