According to the failure model (Patterson & Capaldi, 1990), peer rejection is the intermediary link between problem behaviors and internalizing symptoms. The present study tested the model with 464 monozygotic and same-sex dizygotic twin pairs (234 female, 230 male dyads). Teacher-reported reactive aggression and internalizing symptoms, and…

Preterm birth and Neonatal Intensive Care Unit (NICU) stay are early adverse stressful experiences, which may result in an altered temperamental profile. The serotonin transporter gene ("SLC6A4"), which has been linked to infant temperament, is susceptible to epigenetic regulation associated with early stressful experience. This study…

Analyzed genetic and environmental contributions to intellectual change in 258 adopted and 93 biological children of 3-14 years. The effect of genes and family environment was significant at the time of the first measurement, but only genes made an additional contribution between the first and the second. (RJC)

Describes evolutionary developmental psychology as the study of the genetic and ecological mechanisms that govern the development of social and cognitive competencies common to all human beings and the epigenetic (gene-environment interactions) processes that adapt these competencies to local conditions. Outlines basic assumptions and domains of…

Two cohorts of same-sex twin pairs were assessed on grammar and vocabulary. Findings indicated that vocabulary and grammar correlated strongly at 2 and 3 years in both cohorts, with a consistently high genetic correlation between vocabulary and grammar at both ages. Findings suggest that the same genetic influences operate for vocabulary and…

Examined influences on children's behavior problems in households defined by marital status and sibling relatedness. Found that genetic influences accounted for 81 to 94 percent of mean-level difference in behavior problems between two-parent/full sibling, and the mother-only/half sibling groups. Shared environmental influences accounted for 67 to…