Birth order differences in education originate in postnatal environments

Abstract

Siblings share many environments and much of their genetics. Yet, siblings turn out different. Intelligence and education are influenced by birth order, with earlier-born siblings outperforming later-borns. We investigate whether birth order differences in education are caused by biological differences present at birth, that is, genetic differences or in-utero differences. Using family data that spans two generations, combining registry, survey, and genotype information, this study is based on the Norwegian Mother, Father and Child Cohort Study (MoBa). We show that there are no genetic differences by birth order as captured by polygenic scores (PGSs) for educational attainment. Earlier-born have lower birth weight than later-born, indicating worse uterine environments. Educational outcomes are still higher for earlier-born children when we adjust for PGSs and in utero variables, indicating that birth order differences arise post-natally. Finally, we consider potential environmental influences, such as differences according to maternal age, parental educational attainment, and sibling genetic nurture. We show that birth order differences are not biological in origin, but pinning down their specific causes remains elusive.

Sibship and Inequality Beliefs: Do Siblings Have a Liberalizing or Conservatizing Effect?

“…The weight of sociological research on educational outcomes suggests more spread out spacing, and smaller sibship sizes have positive effects. While Steelman et al 2002 find that birth order has little to no impact on such outcomes, more recent scholarship points to a significant positive association between first-born siblings and educational attainment (Isungset et al 2022). Of particular interest to our outcome measures of inequality beliefs, Freese et al (1999) find that birth order is not a consistent predictor of social attitudes.…”

“…2002 find that birth order has little to no impact on such outcomes, more recent scholarship points to a significant positive association between first‐born siblings and educational attainment (Isungset et al. 2022). Of particular interest to our outcome measures of inequality beliefs, Freese et al.…”

Intergenerational transmission of education and mental health

“…Siblings can affect each other in ways that are complex and might be difficult to observe directly. Sibling effects can differ in their direction (positive or negative, cooperative or competitive) or on their symmetry (siblings affecting each other concurrently or only one sibling influencing another) 359,360 , which can depend on additional sibling characteristics such as birth order or gender 361,362 . Moreover, the sibling effects do not have to originate from the siblings themselves, but can also result from parental behaviour, for example compensating or amplifying differences between siblings 363,364 .…”