Birth Order Differences in Education Originate in Postnatal Environments

In this article, Martin Isungset, Torkild Lyngstad and co-authors investigate if birth order differences in education are caused by genetic differences. Their findings show that birth order differences are not biological in origin, but pinning down their specific causes remains elusive.

Front page of the Journal PNAS Nexus

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. IsungsetLyngstad and co-authors 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).

They 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 postnatally. Finally, they consider potential environmental influences, such as differences according to maternal age, parental educational attainment, and sibling genetic nurture. They show that birth order differences are not biological in origin, but pinning down their specific causes remains elusive.

Read the article.

Tags: Birth order, Education, Genetics, Birth weight
Published Nov. 8, 2022 12:00 PM - Last modified Nov. 8, 2022 12:00 PM