Stability of genetic and environmental influences on reading performance at 7, 12, and 16 years of age in the Colorado Adoption Project

The etiology of the longitudinal stability of reading performance was asses sed by analyzing data from adoptive and nonadoptive sibling pairs (206 pair s at age 7, 195 pairs at age 12, and 110 pairs at age 16) tested in the Col orado Adoption Project (CAP). Results of longitudinal behavioral genetic an alyses confirmed previous findings of moderate genetic influence on individ ual differences in reading performance at 7 and 12 years of age (a(2) = .44 and .38, respectively), with somewhat higher heritability at age 16 (a(2) = .57). Corresponding shared environmental influences were negligible (c(2) = .07, .09, and .07). Moreover, common genetic influences were responsible for 66% of the observed stability (r(p)) between ages 7 and 12 (.62), 62% of that between ages 12 and 16 (r(p) = .74), and 88% of that between ages 7 and 16 (r(p) = .55). Of particular interest, no new heritable variation wa s detected at either 12 or 16 years of age, suggesting that genetic influen ces at 7 years of age are amplified at the later ages. In contrast, new non shared environmental influences (including measurement error) were manifest ed at each age, suggesting the possible importance of nonshared environment al factors (e.g., instructional methods, teachers, peers) for the developme nt of individual differences in reading performance between 7 and 16 years of age.