Genetic and environmental influences on academic achievement were investigated in four groups of siblings: (1) White full siblings, (2) White half-siblings, (3) Black full siblings, and (4) Black half-siblings. Our expectation was that the variances and covariances among three achievement tests would have the same structure across the four groups. This expectation was confirmed by a quantitative genetic model that imposed equal factor loadings across groups. This best fitting model had two factors: a Genetic factor representing genetic variation and a Shared Environment factor representing environmental differences among families. Reading recognition, reading comprehension, and mathematics tests all loaded on the Genetic factor, but primarily mathematics loaded on the Shared Environment factor. The quantitative genetic model was next fit to the achievement test means. Its successful fit suggested that the genetic and environmental influences involved in producing individual variation were the same as those producing the group-mean differences. In this sample, genes accounted for 66% to 74% of the observed group difference in verbal achievement and 36% of the difference in mathematics achievement. Shared environment accounted for the remainder, 34% to 26% of the difference in verbal achievement and 64% of that in mathematics achievement.
All Science Journal Classification (ASJC) codes
- Experimental and Cognitive Psychology
- Developmental and Educational Psychology
- Arts and Humanities (miscellaneous)