Genetic and environmental influences on temperament in middle childhood: Analyses of teacher and tester ratings

Parent ratings of temperament in infancy and childhood yield evidence for genetic influence in twin studies but not in adoption studies. The present study used the sibling adoption design to investigate teacher and tester ratings of temperament in middle childhood. When each child was 7 years old, ratings on the Colorado Childhood Temperament Inventory were obtained from a teacher and tester for more than 50 pairs each of adoptive and nonadoptive siblings in the Colorado Adoption Project. Significant genetic influence emerged for both teacher and tester ratings of Activity, for tester ratings of Sociability, and for teacher ratings of Emotionality. Results obtained from bivariate genetic analysis suggest that the modest covariance between teacher and tester ratings of Activity is entirely mediated genetically. Except for teacher ratings of Attention Span, evidence of shared family environment was nonsignificant, despite the power of the sibling adoption design to detect it.