Abstract
Personality traits such as openness, conscientiousness, and agreeableness predict important life outcomes, and fostering them is therefore a major policy goal. A key modifiable factor that is thought to influence personality is the parenting individuals receive when they are young. However, there is little empirical evidence on the potential impact of parenting on personality traits beyond early adolescence, particularly using causally informative designs. Here, we tested whether mothers' affection toward their children between ages 5 and 10 predicted Big Five personality traits at age 18, when young people leave the structured environment of secondary school and make an important transition to work or further education. We used a prospective longitudinal twin-differences design that compares identical twins growing up in the same family to rule out key confounders and strengthen causal inference. Participants were 2,232 British twins (51.1% female) who had been followed from birth to age 18 as part of the Environmental Risk Longitudinal Twin Study. Twins who had received more affectionate parenting during their childhood years were rated as more open, conscientious, and agreeable young adults by research workers, even when compared with their genetically identical cotwins. There were no differences in extraversion and neuroticism. Associations were small, but they survived stringent robustness checks, including controlling for reporting source, childhood maltreatment, child effects on parenting, and family support at age 18. Our findings suggest that interventions to increase positive parenting in childhood have the potential to make a positive population-wide impact through small but sustained effects on personality traits.