Inherited aspects of cognition become more evident with age

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Original Article

Molecular Psychiatry advance online publication 2 June 2009; doi: 10.1038/mp.2009.55

The heritability of general cognitive ability increases linearly from childhood to young adulthood

C M A Haworth¹, M J Wright², M Luciano², N G Martin², E J C de Geus³, C E M van Beijsterveldt³, M Bartels³, D Posthuma^3,4,5, D I Boomsma³, O S P Davis¹, Y Kovas¹, R P Corley⁶, J C DeFries⁶, J K Hewitt⁶, R K Olson⁶, S-A Rhea⁶, S J Wadsworth⁶, W G Iacono⁷, M McGue⁷, L A Thompson⁸, S A Hart⁹, S A Petrill⁹, D Lubinski¹⁰ and R Plomin¹

1. King's College London, Social, Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London, UK
2. Queensland Institute of Medical Research, Brisbane, QLD, Australia
3. Faculty of Psychology and Education, Department of Biological Psychology, VU University, Amsterdam, The Netherlands
4. Section of Medical Genomics, VU Medical Centre, Amsterdam, The Netherlands
5. Section of Functional Genomics, Faculty of Earth and Life Science, VU University, Amsterdam, The Netherlands
6. Institute for Behavioral Genetics, University of Colorado at Boulder, Boulder, CO, USA
7. Department of Psychology, University of Minnesota, Minneapolis, MN, USA
8. Department of Psychology, Case Western Reserve University, Cleveland, OH, USA
9. Human Development and Family Science, Ohio State University, Columbus, OH, USA
10. Department of Psychology and Human Development, Vanderbilt University, Nashville, TN, USA

Correspondence: Professor R Plomin, King's College London, Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. E-mail: Robert.Plomin@iop.kcl.ac.uk

Received 6 February 2009; Revised 27 April 2009; Accepted 4 May 2009; Published online 2 June 2009.

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Abstract

Although common sense suggests that environmental influences increasingly account for individual differences in behavior as experiences accumulate during the course of life, this hypothesis has not previously been tested, in part because of the large sample sizes needed for an adequately powered analysis. Here we show for general cognitive ability that, to the contrary, genetic influence increases with age. The heritability of general cognitive ability increases significantly and linearly from 41% in childhood (9 years) to 55% in adolescence (12 years) and to 66% in young adulthood (17 years) in a sample of 11 000 pairs of twins from four countries, a larger sample than all previous studies combined. In addition to its far-reaching implications for neuroscience and molecular genetics, this finding suggests new ways of thinking about the interface between nature and nurture during the school years. Why, despite life's 'slings and arrows of outrageous fortune', do genetically driven differences increasingly account for differences in general cognitive ability? We suggest that the answer lies with genotype–environment correlation: as children grow up, they increasingly select, modify and even create their own experiences in part based on their genetic propensities.