Bouchard and McGue (1981) wrote a review article (linked here) that summarized the correlations between relatives.

McGue asserted in a recent talk (that I'm not able to link) that he's not aware of any more recent work that has updated these figures.

However, I suspect that during the last 25 years something must have been done.

I am most interested in the figures for genetically related reared-together relatives, although data on genetically unrelated people reared-together and genetically related reared-apart relatives would also be welcome.

Here are the 1981 correlations for genetically related reared-together relatives. Correlations for genetically related reared-together relatives

Bouchard, T. J., & McGue, M. (1981). Familial studies of intelligence: A review. Science, 212(4498), 1055-1059.

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    $\begingroup$ While IQ changes with time (Flynn effect), why would genetic effects on IQ change? $\endgroup$ – user3116 Aug 5 '15 at 10:27
  • $\begingroup$ Let's say there's a disease that, if contracted by a pregnant woman, would always cause the child to have an IQ of 70 irrespective of what the IQs of the parents are. Then that disease was eradicated. Under those conditions you'd expected to see the parent-child IQ correlations rising. That's just a hypothetical example, but reductions in disease and malnourishment may have exerted analogous effects in reality. $\endgroup$ – user1205197 Nov 11 '15 at 7:29

Recent studies on this topic deal with more detailed questions, that are analysed using structural equation models (Deary et al., 2006). A main goal has been the identification of specific genes. No single genes have been found until today and Sternberg (2012) also points out that the concept of heritability itself is indirect and maybe inappropriate if measured as ratio of genetic variation, because of neglection of cultural factors.

But yes, there has been a meta-analysis since Bouchard and McGue: Daniels et al. (1997) argue for maternal womb effects, that explain "20% of covariance between twins and 5% between siblings". E. g. the IQ correlation for monozygotic twins being raised together is reported as r=.85. Correlations for dizygotic twins raised together are reported as from r=.46 to .60, siblings IQ values correlate from .44 to .46, depending on the statistical model used. In regard to correlations, the findings seem very comparable to Bouchard and McGue's.

And of course, occasionally there have been studies on this fundamental topic, e.g Van Leeuwen (2008), Pujol et al. (2007).


  • Daniels, M., Devlin, B., & Roeder, K. (1997). The heritability of IQ. In Nature (Bd. 388, S. 468–471). LONDON: MACMILLAN MAGAZINES LTD. doi:10.1038/41319
  • Nichols, R. C. (1965). The national merit twin study. Methods and goals in human behavior genetic, 231-244.
  • Van Leeuwen, M., van den Berg, S. M., & Boomsma, D. I. (2008). A twin-family study of general IQ. In Learning and Individual Differences (Bd. 18, S. 76–88). AMSTERDAM: Elsevier Inc. doi:10.1016/j.lindif.2007.04.006
  • David Gallardo Pujol, Uwe Kramp, Carlos García-Forero, Albert Maydeu-Olivares, und Antonio Andrés-Pueyo. (2007). IQ heritability estimation: Analyzing genetically-informative datawith structural equation models. In Psicothema. Universidad de Oviedo.
  • Wahlsten, D. (1994). The intelligence of heritability. Canadian Psychology/Psychologie canadienne, 35(3), 244.
  • Sternberg, R. J. (2012). Intelligence. Wiley Interdisciplinary Reviews: Cognitive Science, 3(5), 501-511.

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