Does the heritability of cognitive abilities vary as a function of parental education? Evidence from a German twin sample

Abstract

A well-known hypothesis in the behavioral genetic literature predicts that the heritability of cognitive abilities is higher in the presence of higher socioeconomic contexts. However, studies suggest that the effect of socioeconomic status (SES) on the heritability of cognitive ability may not be universal, as it has mostly been demonstrated in the United States, but not in other Western nations. In the present study we tested whether the importance of genetic and environmental effects on cognitive abilities varies as a function of parental education in a German twin sample. Cognitive ability scores (general, verbal, and nonverbal) were obtained on 531 German twin pairs (192 monozygotic, 339 dizygotic, ranging from 7 to 14 years of age; Mage = 10.25, SD = 1.83). Data on parental education were available from mothers and fathers. Results for general cognitive ability and nonverbal ability indicated no significant gene x parental education interaction effect. For verbal ability, a significant nonshared environment (E) x parental education interaction was found in the direction of greater nonshared environmental influences on verbal abilities among children raised by more educated parents.

Fig 1. Continuous moderator model for a single twin (see [47]).

The measured moderator (M) has a mediating or main effect (β_M) on the trait (T), as well as a potential moderating effect on the variance components of the residual (after the main effect has been partialled out). A, C, and E represent additive genetic, shared environmental, and nonshared environmental influences on the trait; a, c, e, are the unmoderated elements of genetic, shared, and nonshared path coefficients; M_i is the measured moderator level for the i_th twin pair (both twins in a pair have the same value for obligatorily-shared moderators like SES); μ = the mean of the trait (T); 1 = the constant by which μ is multiplied, values of the trait are given by 1μ+ β_M.

Fig 2. Graphical representation of the G×PE interaction on cognitive abilities.

Variance in cognitive-test performance for the three cognitive ability scores accounted for by genetic and environmental factors, graphed as a function of parental education. a) displays the results derived from the Purcell modeling approach; grey line represents the total variance b) displays the results for verbal ability derived from the LOSEM modeling approach. Cognitive test scores were standardized to a z-scale prior to model fitting.