Sibling relationship quality and parental rearing style influence the development of Dark Triad traits

Currently our understanding of environmental factors that influence the development of dark personality traits (DT) is limited. Therefore, we conducted three studies using online questionnaires, each examining a different aspect of the relation between dark personality traits and family environment. In Study 1, 117 adults (mean age: 30.36 years, SD = 10.19) filled out questionnaires regarding their childhood relationship with siblings and their own DT traits. We found that the amount of conflicts with siblings during adolescence correlated positively with Machiavellianism and psychopathy. The feeling of closeness towards the siblings showed negative correlation with Machiavellianism. Parental partiality towards the other sibling was positively correlated with narcissism. In Study 2, 111 adolescents (mean age: 15.92, SD = 1.24) reported their perceptions of the rearing style of their parents, in addition to their sibling relationships and DT traits. Perceived parental emotional warmth was negatively associated, whereas both rejection and overprotection were positively correlated with psychopathy. Parental warmth was positively, while rejection negatively associated with narcissism. Machiavellianism was positively associated with the amount of conflicts with siblings, but negatively with closeness to siblings. In Study 3, 110 adults (mean age: 32.62 years, SD = 12.25) reported their levels of the Vulnerable Dark Triad that included measures of primary and secondary psychopathy, maladaptive covert narcissism, and borderline personality organization. Results indicated that sibling relation quality had a significant effect on primary psychopathy and borderline traits. Parental rejection and overprotection correlated with borderline traits and vulnerable narcissism. The results of these studies shed some light on how environmental impulses, particularly the quality of relationships between family members, affect the development of personality.