Familial Studies of Intelligence

Where does your general intelligence level come from? Is this a trait that is heritable, that is, you get it from your parents genes? Or is it a function of the kind of environment in which you were raised?

The answer to this nature versus nurture question is obviously both. But how much does nature, your genetics, contribute?

To help answer this question, Thomas Bouchard and Mathew McGue (1981) summarized the results of many studies on the heritability of IQ. These studies correlated the IQ scores of people with different degrees of genetic relationship. It is important to remember that identical twins share 100% of their genes while brothers and sisters and fraternal twins share 50% of their genes.

Their results indicate, for instance, that even when identical twins are raised apart their IQ's still correlated quite highly. This suggests that our genes do contribute to our intelligence level. That is, heredity does play an important part.

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Familial Studies of Intelligence. A review. Bouchard, T. J., & McGue, M. 1981. Science, 212, 1005-1059.