Heritability of General Intelligence
Contributor: Ashley Smith Watts, M.A., Department of Psychology and Neuroscience, Institute for Behavioral Genetics, University of Colorado Boulder
Twin, sibling, and adoption studies provide an important foundation for understanding the heritable and environmental influences on many traits, including intellectual abilities. Previous research has established that general intelligence (as measured by IQ) is highly heritable. However, the picture is complicated by differential heritability estimates across development. For example, genetics seem to play a larger role in influencing intelligence in adulthood, whereas environment plays a larger role in early childhood. Recent studies have examined the interplay between nature and nurture of IQ, and found that the interplay is further complicated by individual differences in intelligence, particularly in adolescence.
The Nature and Nurture of High IQ: An Extended Sensitive Period for Intellectual Development
IQ predicts many measures of life success, as well as trajectories of brain development. Prolonged cortical thickening observed in individuals with high IQ might reflect an extended period of synaptogenesis and high environmental sensitivity or plasticity. We tested this hypothesis by examining the timing of changes in the magnitude of genetic and environmental influences on IQ as a function of IQ score. We found that individuals with high IQ show high environmental influence on IQ into adolescence (resembling younger children), whereas individuals with low IQ show high heritability of IQ in adolescence (resembling adults), a pattern consistent with an extended sensitive period for intellectual development in more-intelligent individuals. The pattern held across a cross-sectional sample of almost 11,000 twin pairs and a longitudinal sample of twins, biological siblings, and adoptive siblings. [Brant, A.M., Munakata, Y., Boomsma, D.I., DeFries, J.C., Haworth, C.M.A., Keller, M.C., Martin, N.G., McGue, M., Petrill, S.A., Plomin, R., Wadsworth, S.J., Wright, M.J., & Hewitt, J.K. (2013). Psychological Science, 24(8), 1487-95.]
NPR Podcast relating to the above article: http://www.npr.org/blogs/health/2013/09/23/224387862/smart-teenage-brains-may-get-some-extra-learning-time
- Briley, D.A. & Tucker-Drob, E.M. (2013). Explaining the increasing heritability of cognitive ability across development: A meta-analysis of longitudinal twin and adoption studies. Psychological Science, 24(9), 1704-13.
- Molenaar, D., van der Sluis, S., Boomsma, D.I., Haworth, C.M.A., Hewitt, J.K., Martin, N.G., Plomin, R., Wright, M.J., & Dolan, C.V. (2013). Genotype by environment interactions in cognitive ability: A survey of 14 studies from four countries covering four age groups. Behavior Genetics, 43, 208-19.