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.
Bibliographical noteFunding Information:
The GHCA consortium is supported by a grant from the John Templeton Foundation (no. 13575). The opinions expressed in this report are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. We thank Andrew McMillan for his support with data management. Support obtained for the GHCA consortium members’ twin studies are as follows. Western Reserve Reading Project (Ohio): US National Institute of Child Health and Human Development (HD038075 and HD046167). Twins Early Development Study (United Kingdom): UK Medical Research Council (G0500079) and the US National Institute of Child Health and Human Development (HD044454 and HD046167). Minnesota Twin Family Study (USA): USPHS grants AA009367, R01 DA005147 and R01 DA013240. Colorado Twin Studies (USA)—LTS: HD19802, HD010333, HD18426, MH043899 and the MacArthur Foundation; CTS: VA1296.07.1629B and DA011015; CLDRC: HD11681 and HD027802. Twin Cognition Study (Australia): Australian Research Council (A7960034, A79906588, A79801419, DP0212016 and DP0343921) and The Human Frontier Science Program (RG0154.1998-B). Netherlands Twin Register: Dutch Organization for Scientific Research (NWO 051.02.060, NWO 480-04-004, NWO 575-25-012 and NWO/SPI 56-464-14192) and Human Frontiers of Science Program (RG0154/1998-B). D Posthuma is supported by NWO/MaGW VIDI-016-065-318.
- behavioral genetics
- genetic variation
- intelligence tests
- quantitative trait