Dramatic increase in heritability of cognitive development from early to middle childhood: an 8-year longitudinal study of 8,700 pairs of twins

Abstract

The generalist genes hypothesis implies that general cognitive ability (g) is an essential target for understanding how genetic polymorphisms influence the development of the human brain. Using 8,791 twin pairs from the Twins Early Development Study, we examine genetic stability and change in the etiology of g assessed by diverse measures during the critical transition from early to middle childhood. The heritability of a latent g factor in early childhood is 23%, whereas shared environment accounts for 74% of the variance. In contrast, in middle childhood, heritability of a latent g factor is 62%, and shared environment accounts for 33%. Despite increasing importance of genetic influences and declining influence of shared environment, similar genetic and shared environmental factors affect g from early to middle childhood, as indicated by a cross-age genetic correlation of .57 and a shared environmental correlation of .65. These findings set constraints on how genetic and environmental variation affects the developing brain.

Figure 1

Longitudinal common pathway model showing genetic and environmental influences on g in early and middle childhood. Squares represent measures of g at each age. Single-headed arrows represent factor loadings; curved double-headed arrows represent correlations between latent factors. Variance is partitioned into additive genetic (A), shared (common) environmental (C), and non-shared environmental (E) influences. The latent factors (circles) at the top represent influences general to early or middle childhood; latent factors at the bottom represent residual variance specific to each age. The numbers and line weights represent parameter estimates, which are presented with confidence intervals in Table 2.