Causation versus selection: A genetically informed study of Marital instability and its consequences for young-adult offspring

III Most studies of the consequences of parental divorce have used statistical controls of measured covariates to account for selection factors, characteristics that influence both parental divorce and the offspring well-being. However, unmeasured characteristics may still confound the association between parental divorce and offspring adjustment. In particular, genetic factors that influence both generations could explain the intergenerational relations. To date, few behavior genetic studies have investigated the underlying mechanisms responsible for adjustment problems associated with parental marital instability. The current project used a genetically informed approach, the Children of Twins Design, to explore the genetic and environmental processes responsible for the higher rates of psychopathology, deleterious life course patterns, and relationship instability in the offspring of divorced families. The analyses utilized samples from Australia and the United States that include adult twins and their young adult offspring. Two general conclusions about divorce can be drawn from the results. First, the amount of variation in marital instability attributable to genetic factors is small. Analyses of the adult twins indicated that environmental factors that make twins dissimilar account for most of the variance in divorce. Second, the risk mechanisms responsible for the associations between parental divorce and offspring adjustment vary across the measures of young adult functioning. Environmental risk factors specifically associated with parental divorce were responsible for the associations between parental marital instability and externalizing problems, substance use and abuse, educational problems, and earlier onset of sexual intercourse and depressive episodes. These findings are consistent with a causal theory of the consequence of divorce. Analyses of the intergenerational IV transmission of relationship instability also underscored the importance of environmentally mediated risk particularly related to parental divorce, but the magnitude of the association was lower than initially estimated because of unmeasured confounds. In contrast, higher rates of depression, earlier onset of drug use, and a greater likelihood to form cohabitating relationships among offspring from divorced families were completely due to selection factors, including genetic confounds. Overall, the results highlight the importance of using genetically informed designs to study environmental risk factors and the need for greater collaboration among behavior genetic, psychological, and sociological researchers.

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