Date of Award
Doctor of Philosophy
This study examined the role of birth complications, delinquent peers and siblings, and specific dopamine receptors on the development of externalizing behavior in children and adolescents, along with the role of heritability in aggression and delinquency. Specifically, it was hypothesized that increased birth complications, presence of specific dopamine receptor (DRD2 and DRD4) risk alleles, and delinquent peers or siblings would be related to increased externalizing behavior at follow-up. The sample consisted of 65 twin pairs, aged six to 16 (mean age = 9.06 years) who originally participated in the Southern Illinois Twins and Siblings Study (SITSS) at age five. Significant results were found for the stability of aggression from age five to follow-up and heritability of parent-rated aggression and delinquency measures was shown. Presence of delinquent peers or siblings was positively related to aggressive and delinquent behavior. Those with more delinquent peers and with the DRD2 risk allele were rated as more delinquent. In contrast, those without the DRD4 risk allele were also rated as more delinquent. Presence of birth complications was positively related to aggressive and delinquent behavior ratings by parents at follow-up. However, birth complications were negatively related to delinquency on youth-rated measures. Finally, those with fewer complications and more delinquent siblings engaged in more reported delinquent behavior. The present study provided important information concerning the effects of birth complications, delinquent peers and siblings, and specific dopamine receptors on the development of externalizing behavior in children and adolescents, along with the role of heritability in aggression and delinquency.
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