Psychopathology is intergenerationally transmitted through both genetic and environmental mechanisms via heterotypic (cross-domain), homotypic (domain-specific), and general (e.g., “p-factor”) pathways. The current study leveraged an adopted-at-birth design, the Early Growth and Development Study (57% male; 55.6% White, 19.3% Multiracial, 13% Black/African American, 10.9% Hispanic/Latine) to explore the relative influence of these pathways via associations between adoptive caregiver psychopathology (indexing potential environmental transmission) and birth parent psychopathology (indexing genetic transmission) with adolescent internalizing and externalizing symptoms. We included composite measures of adoptive and birth parent internalizing, externalizing, and substance use domains, and a general “p-factor.” Age 11 adolescent internalizing and externalizing symptom scores were the average of adoptive parent reports on the Child Behavior Checklist (n = 407). Examining domains independently without addressing comorbidity can lead to incorrect interpretations of transmission mode. Therefore, we also examined symptom severity (like the “p-factor”) and an orthogonal symptom directionality score to more cleanly disentangle transmission modes. The pattern of correlations was consistent with mostly general transmission in families with youth showing comorbid internalizing and externalizing symptoms, rather than homotypic transmission. Findings more strongly supported potential environmental or evocative mechanisms of intergenerational transmission than genetic transmission mechanisms (though see limitations). Parent-specific effects are discussed.

The generalist genes specialist environment model, when applied to developmental psychopathology, predicts that genetic influences should explain variance that is shared across internalizing and externalizing problems, whereas environmental influences should explain variance that distinguishes the two overarching problem types. The present study is a direct test of this hypothesis, leveraging a sample of 708 twins and siblings (aged 10–18 years, 93% White) from the United States. Measures of severity of symptoms, regardless of type, and of directionality of symptoms – whether the adolescent tended to exhibit more externalizing or internalizing problems – were subjected to genetic (A), shared environmental (C), and nonshared environmental (E) (ACE) variance decompositions. As expected, severity of problems was under substantial genetic influence, but there were also significant shared and nonshared environmental influences. Contrary to the generalist genes specialist environment model, directionality of problem type was also under considerable genetic influence, with modest nonshared environmental influence. Findings corroborate existing evidence from other designs highlighting the role of familial influences (including generalist genes) in comorbidity of adolescent internalizing and externalizing problems, but suggest that the specialist environments hypothesis may not be the key factor in distinguishing problem type.