For decades, researchers have observed a curious trend: firstborn children often outperform their younger siblings in both earnings and cognitive abilities. However, pinpointing the exact reasons behind this phenomenon has sparked debate among experts. A recent study offers a compelling new theory, shedding light on the influence of early-life health and other factors.

Early-Life Health and Financial Success

Published by the National Bureau of Economic Research, a working paper delves into the correlation between birth order and earnings based on data from Denmark. The researchers found a significant discrepancy in the likelihood of hospitalization for respiratory conditions during infancy, with younger siblings facing a heightened risk compared to their older counterparts. This increased susceptibility to illness may have long-term financial repercussions, with younger siblings earning 2.4% less on average than their older siblings in adulthood.

Impact on Mental Health and Well-Being

Beyond financial implications, exposure to respiratory illnesses during infancy may impact long-term mental health outcomes. Younger siblings residing in areas with higher rates of infant respiratory illness were more likely to utilize mental-health resources in young adulthood, suggesting a broader ripple effect on well-being.

Contributing Factors Beyond Health

While early-life health disparities explain a significant portion of the earnings gap between siblings, other factors also come into play. Studies across different countries consistently highlight the educational and economic advantages enjoyed by firstborn children. Additionally, parental investment in later-born siblings may diminish, potentially affecting academic performance and skill development.

The Tutor Effect and Sibling Dynamics

Adam Grant’s research underscores the importance of sibling dynamics in shaping cognitive abilities. Firstborns often assume a tutoring role, contributing to their enhanced cognitive performance. Conversely, only children may lack the same opportunities for knowledge transmission, potentially impacting their test scores.

Nature vs. Nurture Debate

Contrary to biological explanations, studies suggest that nurture plays a more significant role in sibling outcomes. Evidence from Norway indicates that younger siblings who had firstborn siblings that died in infancy exhibited higher intelligence scores, emphasizing the influence of environmental factors.

Continued Exploration and Future Implications

While this study offers valuable insights, the complex interplay of factors influencing sibling outcomes warrants further investigation. As researchers continue to unravel the intricacies of birth order effects, policymakers and educators can leverage these findings to design interventions that support equitable opportunities for all children, regardless of their position in the family hierarchy.