- R. Plomin & C Haworth, (2009). INTRODUCTION: Genetics of High Cognitive Abilities. INTRODUCTION: Genetics of High Cognitive Abilities. Behavior Genetics, 39, 347–349
In their introduction to the special issue, the editors state that this is the "first-ever collection of papers focused on the genetics of high cognitive abilities." The focus of the issue is to explore the hypothesis that the etiology of high cognitive ability differs from the etiology of the normal distribution of cognitive ability (aka., Discontinuity Hypothesis; Petrill et al. 2009).
As stated in the intro, "three of the papers focus on general cognitive ability (g), two on reading, one on mathematics, one on a diverse set of intellectual, creative and sports abilities, and one is a multivariate genetic analysis of g, reading, mathematics and language."
Of particular interest is the article by Haworth et al. (2009b) as it "presents a mega-analysis of high g for 11,000 twin pairs across six studies from these four countries. This first adequately powered study of high g (top 15%) finds substantial genetic influence (heritability of 0.50 with a 95% confidence interval of 0.41–0.60) and moderate shared environmental influence (0.28, 0.19–0.37). These estimates are not significantly different from parameter estimates for the entire distribution." The article by Petrill et al., 2009) presents similar findings from their study that investigated high math performance. According to the editors reading of Petrill et al., "genetic and shared environmental estimates for high (top 15%) math ability were not significantly different from those obtained across the normal range of ability." Further support for the Continuity Hypothesis were similar findings by Vinkhuyzen et al. (2009) in their article "Heritability estimates for Music, Arts, Writing, Language, Chess, Mathematics, Sports, Memory and Knowledge." Collectively these different studies are consistent with the Continuity Hypothesis (and not the Discontinuity Hypothesis), which is the view that "high cognitive ability is the quantitative extreme of the same genetic and environmental influences responsible for variation throughout the normal distribution."
Other papers in this special issue report on investigations re: how genes and environment interact developmentally. As summarized by the guest editors:
- Brant et al. (2009) show that shared environment decreases from infancy to adolescence, heritability increases, and genes largely account for age-to-age stability.
- Kirkpatrick et al. ( 2009) confirm in a study of adolescent twins that high cognitive ability shows significant shared environmental influence and then use the power of the adoption design to ask the extent to which parental education and occupation and disruptive life events can account for this shared environmental influence.
- Friend et al. ( 2009) report an interesting genotype– environment interaction between high reading ability and parental education: The heritability of high reading ability was higher for twins when parents were less well educated, which the authors interpret as indicating a genetic effect on resilience in the face of environmental disadvantage.
- Finally, a paper by Haworth et al. ( 2009a) for the first time tests the generalist genes hypothesis for high ability. A multivariate genetic analysis of general cognitive ability, reading, mathematics and language performance for the top 15% of the distribution yields genetic correlations just as high among these diverse cognitive abilities as has been found in unselected samples.