To Each His Own

Little kids have no shortage of personality—but as they age, research suggests, their personalities become gradually more distinct from one another. A study in the Journal of Personality and Social Psychology finds more evidence that the degree of personality difference between kids increases over the course of childhood. The results also go even further, illuminating the role that genes may play in this process.

A team of researchers analyzed data on the Big Five personality traits—openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism—that came from a sample of more than 2,900 Texas youths ages 8 to 21, derived from both the participants’ self-ratings and ratings by their parents. The researchers were interested in the variance of the ratings on each trait—the extent to which individuals higher or lower on a trait tended to differ.

For all traits besides openness, there was consistent evidence that older children were less similar to each other in their ratings than were younger children. University of Edinburgh psychologist and lead study author René Mõttus and his colleagues have found a similar overall trend in samples from Russia, Germany, and Norway as well. Importantly, however, because the study involved participants who were twins—either genetically identical or fraternal—the team was equipped to estimate how much genetic and environmental factors contributed to the increase in distinctiveness.

Their analysis supports the idea that the individuation is driven by genetic factors. But part of the effect, Mõttus says, may be due to the ways differently inclined children interact with the world. Children with a genetic propensity for extraversion, he explains, may “practice social skills and get positive feedback, which makes them even more extraverted.” Those whose genes tip them toward intraversion might drift in the opposite direction. By adulthood, those higher or lower on a given trait may be observably more distinct from one another than when they started out.