Isungset Martin Arstad, Freese Jeremy, Andreassen Ole A, Lyngstad Torkild Hovde
Department of Sociology and Human Geography, University of Oslo, PO Box 1096, Blindern, 0317 Oslo, Norway.
Department of Sociology, Stanford University, Stanford, CA 94305, USA.
PNAS Nexus. 2022 Jun 9;1(2):pgac051. doi: 10.1093/pnasnexus/pgac051. eCollection 2022 May.
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 postnatally. 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.
兄弟姐妹共享许多环境因素以及大部分基因。然而，兄弟姐妹却各不相同。智力和受教育程度受出生顺序影响，出生顺序靠前的兄弟姐妹表现优于靠后的。我们研究教育方面的出生顺序差异是否由出生时就存在的生物学差异导致，即基因差异或子宫内差异。本研究使用跨越两代人的家庭数据，结合登记、调查和基因型信息，基于挪威母亲、父亲和儿童队列研究（MoBa）。我们发现，就教育成就的多基因分数（PGS）而言，出生顺序不存在基因差异。出生顺序靠前的出生体重低于靠后的，这表明子宫环境更差。当我们对PGS和子宫内变量进行调整后，出生顺序靠前的孩子的教育成果仍然更高，这表明出生顺序差异出现在出生后。最后，我们考虑了潜在的环境影响，比如根据母亲年龄、父母教育程度和兄弟姐妹基因培育的差异。我们表明，出生顺序差异并非源于生物学因素，但其具体成因仍难以确定。
