Abstract
The niche-picking principle has been proposed to explain stabilization in personality development and personality continuity in adulthood. The niche-picking principle posits that the reciprocal exchange between people and their environments-person-environment transaction-serves to maintain trait continuity, thereby preserving rank-order stability of trait differences. To date, however, no longitudinal twin study has directly tested whether reciprocal effects between people and their environments contribute to trait continuity in middle and older adulthood. Using a sample of twins from the Swedish Adoption/Twin Study of Aging, we tested whether the niche-picking principle explained stability of longitudinal within-family differences in neuroticism, extraversion, and openness across two stages of adult development. Genetic simplex models that include a reciprocal effects (i.e., phenotype-environment covariance) parameter were fit to twins' longitudinal data. Results suggest that the niche-picking principle partly explains continuity of neuroticism and openness in middle adulthood whereas it partly explains continuity of neuroticism and extraversion in older adulthood. Stable genetic and unique environmental variance also explained continuity of each trait. Findings partially support lifespan developmental theories that posit that people adapt to and possibly optimize behaviors to sustain existing traits. We discuss the importance of the reciprocal exchange between people and their environments across the lifespan and how these exchanges might shift to support trait continuity. (PsycInfo Database Record (c) 2026 APA, all rights reserved).