The Colorado Adoption Project

This paper describes the Colorado Adoption Project (CAP), an ongoing genetically informative longitudinal study of behavioral development. We describe the features of the adoption design used in CAP, and discuss how this type of design uses data from both parent–offspring and related- versus unrelated-sibling comparisons to estimate the importance of genetic and shared environmental influences for resemblance among family members. The paper provides an overview of CAP's history, how subjects were ascertained, recruited, and retained, and the domains of assessment that have been explored since the CAP's initiation in 1975. Findings from some representative papers that make use of data from CAP participants illustrate the study's multifaceted nature as a parent–offspring and sibling behavioral genetic study, a study that parallels a complimentary twin study, a longitudinal study of development, a source of subjects for molecular genetic investigation, and a study of the outcomes of the adoption process itself. As subjects assessed first at age 1 approach age 40, we hope the CAP will establish itself as the first prospective adoption study of lifespan development.

Stability of Genetic and Environmental In‘uences on Reading Performance at 7 and 12 Years of Age in the Colorado Adoption Project

Results obtained from longitudinal studies suggest that individual differences in reading performance are relatively stable over time. However, the aetiology of this stability has not been previously explored. In the current study, the aetiology of longitudinal stability of reading performance between 7 and 12 years of age was assessed using data from adoptive (97 unrelated sibling pairs at age 7 and 73 pairs at age 12) and nonadoptive (106 related pairs at age 7 and 75 pairs at age 12) children tested in the Colorado Adoption Project. Results of a bivariate behavioural genetic analysis confirmed earlier findings of moderate genetic influence on individual differences in reading performance at both 7 and 12 years of age ( h2 = .49 and .37, respectively). Moreover, about 70% of the observed stability ( r = .61) between the two ages was due to common genetic influences. Of special interest, no new heritable or shared environmental variation was manifested at age 12, suggesting that the same genetic and shared environmental influences were operating at both ages. In contrast, nonshared environmental influences (e.g. instructional methods, teachers, peers, etc.) were responsible for change between 7 and 12 years of age, indicating the salience of such factors for the development of reading performance between middle childhood and adolescence.