Background: More highly educated parents tend to raise children who go on to complete more education themselves. Strong evidence for environmental transmission arises from the fact that offspring outcomes correlate to parental genotypes even when controlling for the offspring genotype. The process that gives rise to an environmentally mediated correlation between parental genotype and offspring education (“indirect genetic effects”) remains poorly understood. A key question is whether intergenerational transmission reflects within-family processes, such as parenting behaviors (i.e. “Genetic nurture”), or social inheritance that could reflect either genetic ancestry or social stratification (i.e. “Dynastic effects”).
Methods: Baier, Lyngstad and co-authors analyzed data from N = 25,215 genotyped parent-offspring trios participating in the Norwegian Mother, Father, and Child Cohort Study (MoBa), where many of the participants in the parental generation are siblings (N = 3,500 sibling pairs). They correlate genetic differences within the parental family, conditional on offspring genetics to offspring’s educational outcomes. The strategy isolates indirect genetic effects that play out in the nuclear family from indirect genetic effects that arise through social or ancestral genetic stratification. They additionally partition genetic variants associated with EA into those associated with cognitive versus non-cognitive skills.
Results: They find that children’s genetics, measured using polygenic indices (PGIs) for cognitive and non-cognitive components of EA, are associated with their educational performance. Parents’ genetics are also associated with their children’s educational performance, over and above the child’s own genetics. However, they find no evidence that parents’ PGI are specifically related to offspring academic achievement over and above the average PGI of the siblings in the parental generation.
Conclusions: Their result suggests that the effects of the environmental processes captured by genome-wide association studies of EA and characterized as “nurture” are explained less by parents’ specific behaviors and more by dynastic stratification in environments relevant to success in school.