Birth order differences in education originate in postnatal environments.

Area of Science:

• Behavioral Genetics
• Developmental Psychology
• Sociology

Background:

• Siblings share genetics and environments, yet exhibit developmental differences.
• Birth order is linked to variations in intelligence and educational attainment, with earlier-borns typically achieving higher outcomes.
• The origins of these birth order effects, whether biological or environmental, require further investigation.

Purpose of the Study:

• To determine if birth order differences in educational attainment are rooted in genetic or in utero biological factors.
• To differentiate between prenatal and postnatal influences on birth order-related educational disparities.
• To explore potential environmental factors contributing to these observed differences.

Main Methods:

• Utilized a two-generation family dataset from the Norwegian Mother, Father, and Child Cohort Study (MoBa).
• Combined registry, survey, and genotype information, including polygenic scores (PGSs) for educational attainment.
• Controlled for genetic and in utero variables, including birth weight and maternal factors.

Main Results:

• No significant genetic differences by birth order were found using polygenic scores for educational attainment.
• Earlier-born children had lower birth weights, suggesting potentially less optimal uterine environments.
• Educational outcome advantages for earlier-born children persisted even after adjusting for genetic and in utero factors, indicating postnatal influences.

Conclusions:

• Birth order differences in educational attainment are not attributable to genetic or prenatal biological factors.
• The observed disparities appear to originate from postnatal environmental influences, though specific causes remain unidentified.
• Further research is needed to elucidate the precise environmental mechanisms driving birth order effects on education.