In a shift from the long-held belief that parenting is the primary force in determining a child’s outcomes, a growing body of research indicates that siblings may play an equally significant—if not greater—role in molding each other’s personalities, achievements, and life trajectories. This fresh perspective, featured in the latest cover story of The New York Times Magazine, draws on a range of recent studies examining the “sibling spillover effect,” and is prompting both researchers and families globally, including those in Thailand, to reconsider just how children influence one another within the family unit (NYTimes).
While Thai culture continues to place heavy emphasis on the respect and guidance provided by parents and elders, the research also resonates powerfully in local contexts where extended families are common and siblings may spend significant time together—often in situations where parents are working long hours or resources for extracurricular enrichment are limited. In such households, the bonds between siblings can become the most formative relationships of a child’s early life.
Key developments from The New York Times Magazine investigation, adapted from Susan Dominus’s new book “The Family Dynamic,” reveal that siblings do not simply exist in the shadow of their parents’ parenting style, but actively shape each other. As Dominus and researchers highlight, the so-called “sibling spillover effect” is especially pronounced in families facing economic or social hardship, where siblings may act as role models, sources of advice, and catalysts for ambition.
Importantly, the phenomenon was found not to be exclusive to privileged or high-achieving families. Rather, in disadvantaged households, the influence of siblings may be even more potent, as children rely more on one another for support, friendship, and inspiration when their parents are working or unable to provide constant supervision or structured activities.
The article also challenges the popular narrative around birth order and personality traits. Contrary to widespread belief, robust research indicates that being the eldest does not automatically mean being the most responsible or conscientious child. This misperception, according to leading personality experts referenced in the report, owes more to developmental differences (older children are at a more advanced stage than their siblings while still young) than to inherent traits tied to birth order. Studies, including those published in peer-reviewed journals such as the Journal of Research in Personality, have consistently failed to show that birth order independently predicts major personality dimensions (Wikipedia – Birth Order).
Another intriguing finding relates to the division of interests between siblings. First-borns may enjoy a brief cognitive advantage, attributed to an early period of exclusive parental attention, but younger siblings often carve out unique niches for themselves—such as excelling in sports—often as a means to differentiate themselves and gain recognition apart from their accomplished elder siblings. This niche formation can have long-term effects on self-esteem, ambitions, and even career choices.
Critically, the research exposes the accuracy gap in parental judgments of their children’s strengths. Parents who decide early on which of their children is the “academic” one often see that child outperform the others—sometimes simply because of the confidence and opportunities instilled by that label, not innate ability. Leading scholars on family dynamics warn that such biases can have enduring impacts on educational paths, contributing to the “Pygmalion effect,” where expectations from authority figures shape individuals’ performance (Britannica – Pygmalion Effect).
The question of nature versus nurture also receives nuanced treatment. Rather than pitting genetics and environment against each other, the newest wave of behavioral genetics research suggests a complex interplay: genes can influence which environments we gravitate to, while environmental factors, including sibling relationships, can magnify or diminish genetic propensities. As Dominus notes, parental effort—though well-meaning—might have less influence over a child’s outcomes than most parents expect, with siblings potentially playing a larger role in reinforcing or challenging inherited tendencies.
The findings have clear implications for Thailand’s education and family policy landscape. In a country where large families and multi-generational households are common, and where urban migration often leaves siblings caring for one another, understanding the profound ways siblings shape each other’s development could transform both educational interventions and family support services. School counselors and child psychologists in Thailand are now being called to consider sibling dynamics during assessments, rather than focusing solely on student-parent relationships.
The sociocultural context in Thailand, where “phi-nong” (older-younger sibling) relationships carry formal obligations and expectations, adds another layer of significance to the research. Familial hierarchies are not only recognized, but institutionalized in language, rituals, and daily interactions. Understanding the nuances of these roles—and where modern research diverges from traditional beliefs—could enable families to cultivate more supportive, open, and individualized environments for children.
Looking to the future, experts anticipate a surge in research focused on Asian and Thai families, given the cultural importance of sibling bonds in the region. Policymakers, educators, and family members alike will benefit from integrating these insights into anti-bullying campaigns, parental guidance programs, and youth development initiatives. International studies indicate that interventions leveraging the positive power of sibling relationships—such as mentoring programs that train older siblings to offer academic or emotional support to younger ones—can be especially effective in low-resource settings (NCBI – Sibling Influence).
In practical terms, the evidence suggests Thai parents should refrain from pigeonholing children into simplistic roles (“the smart one,” “the athletic one”) and instead foster an environment where all children are encouraged to explore diverse interests and support one another’s growth. School leaders may consider creating opportunities for siblings to collaborate on projects or mentor each other, bolstering academic and personal development.
For Thai readers navigating family life, these conclusions invite both self-reflection and openness to changing established patterns. The next time siblings argue or compete, parents and guardians can remember that such friction is not only normal but may actually set the stage for children to learn empathy, negotiation, and resilience. The evolving science of sibling relationships offers reassurance that, while every parent’s influence is important, the everyday interactions between siblings may ultimately have the power to shape lives in profound, surprising ways.