A landmark study published in American Psychologist has found that children who received more affectionate mothering between ages 5 and 10 grew up to be more open, conscientious, and agreeable young adults, and the researchers have unusually strong evidence that this relationship is causal, not just a coincidence of genetics.

What the Study Looked At

Researchers from Duke University, King's College London, and the University of Edinburgh followed 2,232 British twins from birth to age 18 as part of the long-running Environmental Risk Longitudinal Twin Study. They measured how affectionate mothers were toward each of their children during childhood, then assessed the young adults' personalities at 18 using outside observers (people who had met the twins but had no connection to their families).

The key question: does the warmth a child receives from their mother actually shape who they become as a person, or does it just look that way because warm parents and warm kids share the same genes?

Why Twins? The Clever Science Behind This Study

Rather than simply comparing different families, researchers compared identical twins within the same family. Because identical twins are genetically identical and share the same home environment, any differences in their personalities as adults can't be explained by genes or family background. They can only be explained by experiences unique to each twin individually.

And here's what researchers found: even between genetically identical twins, the one who received more affectionate parenting during childhood consistently grew up to be more open to new experiences, more conscientious, and more agreeable than their twin who received less.

What the Research Found

• Warm parenting predicted three key personality traits: children who received more maternal warmth between ages 5 and 10 were rated by independent observers at age 18 as significantly more open to experience, more conscientious, and more agreeable, even after accounting for genetics and shared family environment.
• The effects held up under rigorous scrutiny: the researchers tested several alternative explanations and the findings held up in each case.
• The results were consistent whether personality was rated by outside interviewers or by family members, ruling out reporting bias.
• The link persisted even after accounting for childhood maltreatment, meaning this isn't just about the effects of extreme adversity.
• The connection remained even after controlling for whether the child had behavioral or emotional difficulties that might have prompted different parenting in the first place.
• The effects were still present after accounting for family support at age 18, suggesting that childhood parenting (not just ongoing parental involvement) matters.
• Not everything was affected: notably, extraversion (how outgoing a person is) and neuroticism (emotional reactivity and anxiety) did not show the same lasting link to parenting once genetics and family environment were accounted for. These traits appear to be more strongly shaped by genes and factors outside the parent-child relationship.‍
• The effects were small but meaningful: the associations found were modest in size and researchers are careful to note this. But as they point out, even small effects on personality traits like conscientiousness can translate into meaningful differences in life outcomes over time: educational achievement, career success, health, and relationships.

What This Means for Moms

The personality traits most influenced by warm parenting aren't just abstract psychological categories. They predict real-world outcomes across a lifetime.

Conscientiousness (the tendency to be organized, reliable, and follow through on commitments) is one of the strongest known predictors of academic and professional success. Openness to experience relates to curiosity, creativity, and adaptability. Agreeableness shapes how people navigate relationships and conflict.

Children who develop stronger versions of these traits are better equipped to handle the demands of adulthood: managing time and money, building friendships, seeking out opportunities, and coping with new situations. And this study suggests that a mother's warmth during the ages of 5 to 10 is a meaningful part of how those traits develop.

This research doesn't mean that parenting is everything, or that every personality difference between children comes down to how they were raised. Genetics still matter enormously, and the effects found here were modest. However, it does offer something reassuring: the warmth and affection you show your child during their elementary school years appears to leave a real and lasting impression, one that survives into adulthood, and that can't simply be explained away by saying they were "born that way."

You don't need to be a perfect parent. But showing up with warmth, interest, and affection consistently appears to matter in ways that reach well beyond childhood.

Takeaways

• Warmth and affection during the ages of 5 to 10 appears to be a particularly important window. This doesn't mean later parenting doesn't matter, but this period emerged as significant in the data.
• Consistency appears more important than intensity. The study measured parenting across ages 5 and 10, suggesting that sustained warmth over time is what predicts later personality.
• Expressing genuine interest in your child (their thoughts, their experiences, what they're like as a person) is not just nice to do. It may be one of the most durable investments you can make in their development.
• If you're going through a difficult period and feel like you're falling short, the research suggests resilience matters. Even small improvements in warmth and responsiveness can have population-level effects when sustained.

The Bottom Line

This study provides some of the strongest evidence yet that how affectionately a mother parents her child shapes that child's personality as a young adult, and that this effect is real, not just a reflection of shared genes or family circumstances. The traits most influenced (openness, conscientiousness, and agreeableness) are among the best predictors of a flourishing adult life. In short: your warmth matters, and this study suggests it leaves a mark that lasts.

Read the research: Wertz et al., American Psychologist (2025) — Parenting in Childhood Predicts Personality in Early Adulthood: A Longitudinal Twin-Differences Study