A twin-family study of general IQ.

M. van Leeuwen, S.M. van den Berg, D.I. Boomsma

Research output: Contribution to JournalArticleAcademicpeer-review


In this paper we assess the presence of assortative mating, gene-environment interaction and the heritability of intelligence in childhood using a twin family design with twins, their siblings and parents from 112 families. We evaluate two competing hypotheses about the cause of assortative mating in intelligence: social homogamy and phenotypic assortment, and their implications for the heritability estimate of intelligence. The Raven Progressive Matrices test was used to assess general intelligence (IQ) and a persons IQ was estimated using a Rasch model. There was a substantial correlation between spouses for IQ (r = .33) and resemblance in identical twins was higher than in first-degree relatives (parents and offspring, fraternal twins and siblings). A model assuming phenotypic assortment fitted the data better than a model assuming social homogamy. The main influence on IQ variation was genetic. Controlled for scale unreliability, additive genetic effects accounted for 67% of the population variance. There was no evidence for cultural transmission between generations. The results suggested that an additional 9% of observed IQ test variation was due to gene-environment interaction, with environment being more important in children with a genetic predisposition for low intelligence. © 2007 Elsevier Inc. All rights reserved.
Original languageEnglish
Pages (from-to)76-88
JournalLearning and Individual Differences
Issue number1
Publication statusPublished - 2008

Cohort Studies

  • Netherlands Twin Register (NTR)


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