Abstract
The Dickens and Flynn model of the Flynn effect (generational increases in mean IQ) assigns an important role to genotype-environment covariance (GE-cov). We quantify GE-cov in a longitudinal simplex model by modeling it as phenotype to environment (Ph->E) transmission in twin data. The model fits as well as the standard genetic simplex model, which assumes uncorrelated genetic and environmental influences. We use the results to explore numerically the possible role of GE-cov in amplifying increases in environmental means. Given the estimated Ph->E transmission parameters, GE-cov resulted in an amplification (in std units) of a factor 1.57 (full scale IQ) to 1.7 (performance IQ). The results lend credence to the role of GE-cov in the Flynn effect.
Highlights
Dickens and Flynn [1] proposed an elaborate model to account for the Flynn (a.k.a., Lynn–Flynn) effect, i.e., increases in average of psychometric measures of cognitive ability in the order of 2/3 of one standard deviation per 30 years (10 points given a standard deviation of 15) [2,3]
genotype-environment covariance (GE-cov) originating in phenotype to environment (Ph->E) transmission [14,18], which is consistent with the model proposed by Dickens and Flynn [1], and to determine how Ph->E transmission can amplify beneficial
We found that the AE* model including Ph->E transmission fitted the data as well as the ACE simplex model [12]
Summary
Dickens and Flynn [1] proposed an elaborate model to account for the Flynn (a.k.a., Lynn–Flynn) effect, i.e., increases in average of psychometric measures of cognitive ability in the order of 2/3 of one standard deviation per 30 years (10 points given a standard deviation of 15) [2,3]. Their model combines changes in environmental means within a developmental process, which gives rise to genotype-environment covariance (GE-cov). This is notably the case in longitudinal and multivariate modeling within the classical twin design, the estimation of GE-cov has been considered in extended family and twin designs [8,9,10,11]
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