Explaining the increasing heritability of cognitive ability across development: a meta-analysis of longitudinal twin and adoption studies

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.

Keywords: amplification; behavior genetics; childhood development; cognition; cognitive ability; development; intelligence.

Fig. 1

Longitudinal behavioral genetic Cholesky decomposition for one member of a sibling pair. The latent variables A, C, and E represent the influence of genetic variation, shared environmental variation, and nonshared environmental variation, respectively. A₁, C₁, and E₁ represent these influences on cognition at the first measurement occasion (Time 1), and squaring the parameters a₁, c₁, and e₁ gives the proportion of variance in cognitive ability at Time 1 accounted for by the A₁, C₁, and E₁ components, respectively. The parameters labeled a_b, c_b, and e_b represent the carryover of genetic and environmental effects from Time 1 to the second measurement occasion (Time 2). The latent variables A_u, C_u, and E_u represent the unique variance at Time 2, and the squared a_u, c_u, and e_u parameters represent the proportion of variance attributable to novel influences.

Fig. 2

Predicted amount of change in the proportion of variance accounted for by genes, the shared environment, and the nonshared environment across time intervals between assessments. Shading represents ±1 SE.

Fig. 3

Predicted influence of amplification and innovation effects on variance in cognitive ability at the second time point of measurement across participants' age. Results are shown separately for the influence of (a) genes, (b) the shared environment, and (c) the nonshared environment. Amplification refers to the carryover of early influences across time. Innovation refers to the emergence of novel influences over time. In each graph, shading represents ±1 SE.