The Genetics of Intelligence

There were an endless debate about whether IQ heritability was spuriously inflated, while the growing evience, notably from modern techniques (e.g., GCTA), shows a non-negligible heritability in the narrow sense. A large part of the twin method estimates has been confirmed.

Continue reading

Advertisements

Les gènes de l’intelligence : L’héritabilité estimée par les recherches en génétique comportementale

Il existe des débats persistants sur le fait que les estimations d’héritabilité de l’intelligence humaine serait trompeuses, qu’elles masquent des effets de corrélation gène-environnement (GxE). Heureusement, les techniques modernes permettent de tester la plausibilité de cette hypothèse. Une bonne partie des estimations d’héritabilité provenant de la méthode des jumeaux a pu être confirmée, la partie manquante s’expliquerait par la partie manquante de la variance génétique non capturée pour le moment par les techniques modernes. Les preuves d’effet additif de l’héritabilité, néanmoins, sont fortes.

Continue reading

The IQ Deficit : Disease, Climate, and Evolutionary Causes

A widely cited study (Eppig et al., 2010) suggested that infectious disease is the most important determinant of national IQs, independently and above GDP, education and some evolutionary variables. But their analysis is just a hierarchical multiple regression. It does not tell us anything about the arrow of causality. It is plausible that it goes both ways. Their results look like this :

Parasite prevalence and the worldwide distribution of cognitive ability - Table 3

The interesting fact is that they have used Lynn and Vanhanen’s (LVE) as well as Wicherts et al. (WEAM) IQ estimates. They demonstrate that the results are not significantly different for DALY disease and the evolutionary variables, which suggests that L&V estimates are not as inaccurate as is usually said.

Continue reading

Explaining the Increasing Heritability of Cognitive Ability Across Development: A Meta-Analysis of Longitudinal Twin and Adoption Studies

Explaining the Increasing Heritability of Cognitive Ability Across Development: A Meta-Analysis of Longitudinal Twin and Adoption Studies

Daniel A. Briley and Elliot M. Tucker-Drob (2013).
See supplemental materials.

Abstract

Genes account for increasing proportions of variation in cognitive ability across development, but the mechanisms underlying these increases remain unclear. We conducted a meta-analysis of longitudinal behavioral genetic studies spanning infancy to adolescence. We identified relevant data from 16 articles with 11 unique samples containing a total of 11,500 twin and sibling pairs who were all reared together and measured at least twice between the ages of 6 months and 18 years. Longitudinal behavioral genetic models were used to estimate the extent to which early genetic influences on cognition were amplified over time and the extent to which innovative genetic influences arose with time. Results indicated that in early childhood, innovative genetic influences predominate but that innovation quickly diminishes, and amplified influences account for increasing heritability following age 8 years.

Continue reading

The Nature and Nurture of High IQ: An Extended Sensitive Period for Intellectual Development

The Nature and Nurture of High IQ: An Extended Sensitive Period for Intellectual Development

Angela M. Brant, Yuko Munakata, Dorret I. Boomsma, John C. DeFries, Claire M. A. Haworth, Matthew C. Keller, Nicholas G. Martin, Matthew McGue, Stephen A. Petrill, Robert Plomin, Sally J. Wadsworth, Margaret J. Wright, and John K. Hewitt. 2013.

Abstract

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.

Continue reading