A first-of-its-kind, nationally representative study of siblings supports previously published research on unrelated individuals that links specific genotypes to educational attainment among adults in their mid-20s to early 30s.
The research, published Aug. 20 in AERA Open, a peer-reviewed journal of the American Educational Research Association, found that, within families, an adolescent with a higher “polygenic score”—which summarizes previously identified genome-wide associations for educational attainment—than her or his sibling tended to go on to complete more years of schooling.
The authors of the study used genome-wide data from 1,594 siblings in the National Longitudinal Study of Adolescent to Adult Health, also known as Add Health.
While the predicted difference in actual educational attainment between siblings was small—roughly one-third of a year of schooling—the study provides new evidence that recently discovered genetic factors actually do cause differences in educational outcomes, according to lead author Benjamin Domingue, of Stanford University.
“By examining siblings, this study was able to control for external social aspects, such as schools, neighborhoods and level of parental education, to hone in specifically on the role of genes in this complex process,” said Domingue. “The study provides strong evidence that genotype can predict educational attainment within families.”
The researchers were careful to note that they have not discovered “the gene for education” or that these findings somehow imply that a person’s educational attainment is determined at birth.
“It still only explains a very small and trivial amount of the variation, 2 to 4 percent, which means that 97 percent of the reason why individuals do well in school has nothing to with these genes,” said CU-Boulder Institute of Behavioral Science researcher and Department of Sociology Professor Jason Boardman.
Furthermore, the authors found that the association between genetic predisposition and actual educational attainment was of comparable strength within and between families, indicating that family environments may be magnifying a modest genetic difference between siblings. For example, siblings may seek to differentiate themselves from one another, causing them to form identities that drive them toward more or less academic-related activities. The study found no relationship between a sibling’s birth order and his or her polygenic score.
When looking at only African Americans, the genetic effect was found to be smaller but still statistically significant.
“The social environment appears to be more important for educational outcomes for African Americans,” Boardman said. “This is a classic example of an unfair system. Even though someone has pro-education alleles, they don’t manifest an educational benefit by race.”
Boardman also pointed out the results are highly correlated to a point in time. For instance, in the mid-1960s, researchers found no genetic link to smoking because everyone was doing it. Today, smoking is correlated to a certain genotype.
“What manifested as a genetic resource for education for the 1940s might be completely different than what we’re showing now,” Boardman noted.
In another key finding, the study documented that polygenic scores across a broad population sample, going beyond siblings, are associated with social environmental differences.
European Americans with higher polygenic scores tended to live in more socially advantaged neighborhoods and had mothers with higher levels of educational attainment. While African Americans’ polygenic scores were not related to the social circumstances of their neighborhoods, they were associated with maternal level of education.
“We show, for the first time, clear evidence for socio-geographic patterning of polygenic scores in the contemporary United States,” said Domingue. “Neighborhoods can be important facilitators of, or impediments to, children’s social attainments.”
The authors emphasize that while there is a causal relationship between polygenic educational scores and educational attainment, among the general population, social factors still play a more important role in shaping outcomes. For instance, having a mother who graduated from college was associated with an additional 1.7 years of schooling.
The authors also warn that the predictive power of the polygenic educational score is too weak to be used for individual clinical interventions.
“Eventually, this type of research will help us better understand, across broad groups, the complex relationship between genetics, environments, and traits and behaviors, as well as help us better understand why school or government policies may or may not be generating desired objectives,” Domingue said.
Other study authors are Daniel Belsky, of Duke University; Dalton Conley, of New York University; and Kathleen Mullan Harris, of the University of North Carolina, Chapel Hill.