Maintenance of genetic variation in personality through control of mental mechanisms: a test of trust, extraversion, and agreeableness

Since natural selection produces genetically homogeneous populations with regard to adaptively important traits, the relatively high genetic variance associated with human personality is an enigma. In this article, we propose that humans adaptively control the activation of domain-specific mental mechanisms in accordance with personality. This process functions to reduce fitness differences among individuals with different genetic backgrounds associated with personality. Such control would facilitate the evolution of heritable personality traits. We conducted a twin study, showing that the level of general trust (trust of strangers) is controlled not only by environmental factors but also by personality factors, thus producing reactive heritability of general trust. This result supports our hypothesis.