The Development of Machiavellianism, Psychopathy, and Narcissism in Young Adulthood

The development of the personality traits Machiavellianism, psychopathy, and narcissism is hardly understood. We theorize that the well-documented maturity principle applies to these traits. Decreasing levels of Machiavellianism, psychopathy, and the antagonistic dimension “narcissistic rivalry” could be interpreted as reflecting maturation. The self-enhancing “narcissistic admiration” trait might remain unchanged. A sample of N = 926 German university students aged 18 to 30 (74% female) participated in a longitudinal study with 4 waves of measurement over 2 years, completing short and full-length measurement instruments. The preregistered analyses included latent growth curve models based on item factor analysis with partial measurement invariance. We accounted for the possibilities of contextual effects and nonlinear development and controlled the false discovery rate. All four traits showed very high rank-order stability (rs ranged from .74 to .81). In line with the maturity principle, mean levels of Machiavellianism and psychopathy decreased linearly (ds were −0.18 and −0.12). Moreover, model comparisons revealed systematic heterogeneity in Machiavellianism’s linear growth curve, indicating that young adults differ from each other in the direction or steepness of their developmental paths. We also assessed self-esteem and life satisfaction. Linear changes in Machiavellianism were inversely related to linear changes in life satisfaction (r = −.39), making the mean-level decrease in Machiavellianism appear as adaptive. While findings concerning narcissism were inconclusive, this study provides incremental evidence that the maturity principle might apply to Machiavellianism and, potentially, to psychopathy.