Enrollment of both fraternal and identical infant twins in Colorado began in 1985 and continued for a period of 7 years. The purpose of this research is to study the varying genetic and environmental influences on development, including cognition, temperament, physical development, intelligence, and emotion.


  • John Defries

  • John K. Hewitt

  • Robert Plomin

  • Robin Corley

  • Soo Hyun Rhee

  • Sally Wadsworth

  • Akira Miyake

  • Susan Young

Publication Highlights:

1. Friedman, N.P., Miyake, A., Corley, R.P., Young, S.E., DeFries, J.C., & Hewitt, J.K. (2006). Not all executive functions are related to intelligence. Psychological Science, 17,172-179. | pubmed abstract |

2. Young S.E., Rhee S.H., Stallings M.C., Corley R.P. & Hewitt J.K. (2006) Genetic and environmental vulnerabilities underlying adolescent substance use and problem use: general or specific? Behav Genet, 36(4), 603-15 | pubmed abstract |

3.Button, T.M.M., Rhee, S.H., Hewitt, J.K., Young, S.E., Corley, R.P., Stallings, M.C. (2007) The role of conduct disorder in explaining the comorbidity between alcohol and illicit drug dependence in adolescence. Drug and Alcohol Dependence8746-53. |pubmed abstract |