Genetic Ancestry and General Cognitive Ability in a Sample of American Youths

Abstract

Black and Hispanic children in the United States have lower mean cognitive test scores than White children. The reasons for this are contested. The test score gap may be caused by socio-cultural factors, but the high heritability of g suggests that genetic variance might play a role. Differences between self-identified race or ethnicity (SIRE) groups could be the product of ancestral genetic differences. This genetic hypothesis predicts that genetic ancestry will predict g within these admixed groups. To investigate this hypothesis, we performed admixture-regression analyses with data from the Adolescent Brain Cognitive Development Cohort. Consistent with predictions from the genetic hypothesis, African and Amerindian ancestry were both found to be negatively associated with g. The association was robust to controls for multiple cultural, socioeconomic, and phenotypic factors. In the models with all controls the effects were as follows: (a) Blacks, African ancestry: b = -0.89, N = 1690; (b) Hispanics, African ancestry: b = -0.58, Amerindian ancestry: b = -0.86, N = 2021), and (c) a largely African-European mixed Other group, African ancestry: b = -1.08, N = 748). These coefficients indicate how many standard deviations g is predicted to change when an individual's African or Amerindian ancestry proportion changes from 0% to 100%. Genetic ancestry statistically explained the self-identified race and ethnicity (SIRE) differences found in the full sample. Lastly, within all samples, the relation between genetic ancestry and g was partially accounted for by cognitive ability and educational polygenic scores (eduPGS). These eduPGS were found to be significantly predictive of g within all SIRE groups, even when controlling for ancestry. The results are supportive of the genetic model. Keywords: Ancestry, Admixture, education, Intelligence, ABCD cohort