A growing body of research challenges the idea that parenting is the sole driver of a child’s outcomes. Studies on the “sibling spillover effect” indicate that brothers and sisters can influence each other’s personalities, achievements, and life paths as much as, or even more than, parents. The latest adaptation of this theme appears in a recent cover story by The New York Times Magazine, drawing on multiple studies to explore how siblings shape one another. In Thailand, as in many countries, families are rethinking how sibling relationships contribute to development and success.
In Thai households, where extended families and multi-generational living are common, siblings often share the bulk of daily activities, especially when parents work long hours or resources for enrichment are limited. In these settings, the bond between siblings can become a central force in early development, guiding interests, collaboration, and resilience.
Key findings from The New York Times Magazine’s investigation, drawing on Susan Dominus’s new book The Family Dynamic, reveal that siblings do more than exist alongside parental influence. The sibling spillover effect appears strongest in families facing economic or social challenges, where siblings serve as role models, sounding boards, and catalysts for ambition.
The research is not limited to affluent or high-achieving families. In fact, in disadvantaged households, sibling influence may be even more powerful, as children lean on one another for support, friendship, and inspiration when parental supervision is limited or structured activities are scarce.
The article also reconsiders birth order as a predictor of personality. Contrary to common belief, being the oldest does not automatically equate with greater responsibility or conscientiousness. Developmental differences and social context often explain perceived distinctions between siblings more than birth order alone. Essays in reputable journals have consistently shown that birth order does not independently determine major personality traits.
Another interesting insight concerns how siblings divide interests. First-born children may briefly benefit from early parental attention, while younger siblings carve out distinctive niches, such as excelling in sports, to carve their own path. This niche differentiation can influence self-esteem, ambitions, and even career directions.
The analysis highlights how parental labeling can distort expectations. When parents quickly tag one child as the “academic one,” that child may outperform siblings simply due to confidence and opportunities associated with that label, not necessarily because of innate ability. Experts warn that such biases can shape educational trajectories, echoing the broader Pygmalion effect, where expectations shape performance.
Nature and nurture are treated not as opposing forces but as interacting influences. Behavioral genetics now suggests a complex dance: genes steer the environments we seek, while surroundings—including sibling relationships—can amplify or dampen genetic propensities. Parental effort, though well-intentioned, may have less sway over outcomes than commonly assumed, with siblings potentially reinforcing or challenging inherited tendencies.
For Thailand, these findings carry clear implications for education and family policy. In a country with large families and frequent multi-generational living, understanding how siblings influence development could transform educational interventions and family support services. School counselors and child psychologists may begin to consider sibling dynamics as part of assessments, alongside parent-child relationships.
Thai culture’s phi-nong (older-younger sibling) relationships, with formal expectations embedded in language and daily life, add depth to these insights. Recognizing where traditional beliefs diverge from modern research can help families foster more supportive, open, and individualized environments for children.
Looking ahead, researchers expect more focus on Asian and Thai families, given the region’s emphasis on sibling bonds. Policymakers, educators, and families may benefit from applying these insights to anti-bullying campaigns, parental guidance, and youth development programs. International studies also suggest that mentoring programs where older siblings support younger ones can be particularly effective in low-resource settings.
In practical terms, Thai parents are encouraged to avoid pigeonholing children into fixed roles like “the smart one” or “the athlete.” Instead, nurturing a climate where all children explore diverse interests and support one another can promote holistic growth. Schools might create opportunities for siblings to collaborate on projects or mentor each other, strengthening both academic and personal development.
For Thai readers navigating family life, these findings invite reflection and openness to adapt longstanding patterns. When siblings argue or compete, parents can view such moments as opportunities to teach empathy, negotiation, and resilience. The evolving science of sibling relationships offers reassurance that, while parental influence remains important, everyday interactions among siblings can profoundly shape lives.