Parent-Offspring and Sibling Adoption Analyses of Parental Ratings of Temperament in Infancy and Childhood


  • The Colorado Adoption Project is supported in part by grants from the National Institute of Child Health and Human Development (HD-10333 and HD-18426) and the National Science Foundation (BSN-8806589). We are grateful to the families participating in this project who have so generously contributed their time and effort, and to the adoption agencies who made the study possible–Lutheran Social Services of Colorado and Denver Catholic Community Services.

Requests for reprints should be sent to Robert Plomin, Center for Developmental and Health Genetics, College of Health and Human Development, Pennsylvania State University, University Park, PA 16802.


ABSTRACT A first step toward understanding the etiology of personality is to investigate the relative impact of genetic and environmental factors using twin and adoption designs. Twin studies of infants and young children indicate substantial genetic influence for parental ratings of temperament in the preschool years. Adoption studies, however, have not previously been reported during the early years of life. We present parent-off spring comparisons for temperament (emotionality, activity, sociability, and impulsivity) for adopted and nonadopted children yearly from 1 to 7 years of age and their biological, adoptive, and nonadoptive parents. Also presented are correlations for adoptive and nonadoptive siblings when each child was 1, 2, 3, and 4 years of age. In contrast with twin results, little evidence is found for genetic influence. The average correlation between biological parents and their adopted-away children for data averaged over the 7 years is only .03. Similarly, the average parent-off spring correlation in nonadoptive families (.08) is no greater than in adoptive families (.12). Results for nonadoptive and adoptive siblings also indicate little genetic influence. The difference between the twin and adoption results may be due to environmental effects or to nonadditive genetic variance.