Gene × environment interactions in early externalizing behaviors : parental emotional support and socioeconomic context as moderators of genetic influences?
Previous findings on gene × environment interactions on externalizing behaviors have been inconsistent. In an attempt to provide clarity on this inconsistency, our study used two longitudinal population-based samples of young twins to examine the independent effects of two moderators commonly studied in the externalizing literature. Our first sample, the twin subsample from the Early Childhood Longitudinal Study-Birth Cohort (ECLS-B), was composed of approximately 600 twin pairs measured on externalizing at ages 4 and 5. We tested for gene × parental emotional support and gene × socioeconomic status interactions on externalizing. Results indicated stronger genetic influences on externalizing at higher levels of parental emotional support but also at lower levels of socioeconomic status. These moderation effects, however, were not replicated in our analyses of the National Longitudinal Survey of Youth-Child Supplement (C-NLSY) data, which contained 2370 pairs of siblings measured on externalizing at ages 4-5 and ages 6-7. Our results highlight the need for replication in quantitative behavior genetics research on externalizing behaviors.