Narcissism is a personality trait with far-reaching individual, social, and societal consequences. Thus, it is important to understand the sources of individual differences in this trait. Existing hypotheses on the development of narcissism have focused on familial and parental environments that act to make siblings in a family more alike. However, the relative importance of shared environments as opposed to other environmental and genetic sources is still unclear. Using a large extended twin family design, we found that parents’ and children’s narcissism scores were correlated, but this association was entirely genetically driven. Across age and measures, genetics and individual-specific environmental factors each explained 50% of the variance in narcissism, and there was no evidence of environmental sources shared within families. This finding calls for a fundamental shift in the search for the origins of narcissism, including extra-familial environmental factors (e.g., educational and occupational pathways, experiences with peers, and romantic partners).
Back et al. (2026) studied this question.