Racial and ethnic group differences in the heritability of intelligence: A systematic review and meta-analysis

Where you live matters: visualizing environmental effects on reading attainment

BACKGROUND

The way in which socioeconomic status (SES) moderates the etiology of reading attainment has been explored many times, with past work often finding that genetic influences are suppressed under conditions of socioeconomic deprivation and more fully realized under conditions of socioeconomic advantage: a gene-SES interaction. Additionally, past work has pointed toward the presence of gene-location interactions, with the relative influence of genes and environment varying across geographic regions of the same country/state.

METHOD

This study investigates the extent to which SES and geographical location interact to moderate the genetic and environmental components of reading attainment. Utilizing data from 2,135 twin pairs in Florida (mean age 13.82 years, range 10.71-17.77), the study operationalized reading attainment as reading comprehension scores from a statewide test and SES as household income. We applied a spatial twin analysis procedure to investigate how twin genetic and environmental estimates vary by geographic location. We then expanded this analysis to explore how the moderating role of SES on said genetic and environmental influences also varied by geographic location.

RESULTS

A gene-SES interaction was found, with heritability of reading being suppressed in lower- (23%) versus higher-SES homes (78%). The magnitude of the moderating parameters were not consistent by location, however, and ranged from -0.10 to 0.10 for the moderating effect on genetic influences, and from -0.30 to 0.05 for the moderating effect on environmental influences. For smaller areas and those with less socioeconomic variability, the magnitude of the genetic moderating parameter was high, giving rise to more fully realized genetic influences on reading there.

CONCLUSIONS

SES significantly influences reading variability. However, a child's home location matters in both the overall etiology and how strongly SES moderates said etiologies. These results point toward the presence of multiple significant environmental factors that simultaneously, and inseparably, influence the underlying etiology of reading attainment.

Contextualizing Positionality, Intersectionality, and Intelligence in the Anthropocene

The geological epoch of the Anthropocene has challenged traditional definitions of what intellectual abilities are necessary to creatively problem-solve, understand, and address contemporary societal and environmental crises. If we hope to make meaningful changes to how our society addresses these complex issues and pave the way for a better future for generations to come, we must advance traditional theories and measures of higher-order abilities to reflect equity and inclusion. To this end, we must address global issues by integrating the complexities of intersectional identities as they impact our understanding of what constitutes intelligence in individuals, groups, and diverse communities. This re-envisioning of intelligence presents new complexities for understanding and challenges for our field beyond the boundaries of what has been previously touted by many disciplines, including psychology. It is an opportunity to re-envision what it means to be intelligent in a diverse global context while also honoring and recognizing the value of difference, positionality, and other ways of knowing.

Parenting in the Context of the Child: Genetic and Social Processes

The focus on the role of parenting in child development has a long-standing history. When measures of parenting precede changes in child development, researchers typically infer a causal role of parenting practices and attitudes on child development. However, this research is usually conducted with parents raising their own biological offspring. Such research designs cannot account for the effects of genes that are common to parents and children, nor for genetically influenced traits in children that influence how they are parented and how parenting affects them. The aim of this monograph is to provide a clearer view of parenting by synthesizing findings from the Early Growth and Development Study (EGDS). EGDS is a longitudinal study of adopted children, their birth parents, and their rearing parents studied across infancy and childhood. Families (N = 561) were recruited in the United States through adoption agencies between 2000 and 2010. Data collection began when adoptees were 9 months old (males = 57.2%; White 54.5%, Black 13.2%, Hispanic/Latinx 13.4%, Multiracial 17.8%, other 1.1%). The median child age at adoption placement was 2 days (M = 5.58, SD = 11.32). Adoptive parents were predominantly in their 30s, White, and coming from upper-middle- or upper-class backgrounds with high educational attainment (a mode at 4-year college or graduate degree). Most adoptive parents were heterosexual couples, and were married at the beginning of the project. The birth parent sample was more racially and ethnically diverse, but the majority (70%) were White. At the beginning of the study, most birth mothers and fathers were in their 20s, with a mode of educational attainment at high school degree, and few of them were married. We have been following these family members over time, assessing their genetic influences, prenatal environment, rearing environment, and child development. Controlling for effects of genes common to parents and children, we confirmed some previously reported associations between parenting, parent psychopathology, and marital adjustment in relation to child problematic and prosocial behavior. We also observed effects of children's heritable characteristics, characteristics thought to be transmitted from parent to child by genetic means, on their parents and how those effects contributed to subsequent child development. For example, we found that genetically influenced child impulsivity and social withdrawal both elicited harsh parenting, whereas a genetically influenced sunny disposition elicited parental warmth. We found numerous instances of children's genetically influenced characteristics that enhanced positive parental influences on child development or that protected them from harsh parenting. Integrating our findings, we propose a new, genetically informed process model of parenting. We posit that parents implicitly or explicitly detect genetically influenced liabilities and assets in their children. We also suggest future research into factors such as marital adjustment, that favor parents responding with appropriate protection or enhancement. Our findings illustrate a productive use of genetic information in prevention research: helping parents respond effectively to a profile of child strengths and challenges rather than using genetic information simply to identify some children unresponsive to current preventive interventions.

Between-Group Mean Differences in Intelligence in the United States Are >0% Genetically Caused: Five Converging Lines of Evidence

The past 30 years of research in intelligence has produced a wealth of knowledge about the causes and consequences of differences in intelligence between individuals, and today mainstream opinion is that individual differences in intelligence are caused by both genetic and environmental influences. Much more contentious is the discussion over the cause of mean intelligence differences between racial or ethnic groups. In contrast to the general consensus that interindividual differences are both genetic and environmental in origin, some claim that mean intelligence differences between racial groups are completely environmental in origin, whereas others postulate a mix of genetic and environmental causes. In this article I discuss 5 lines of research that provide evidence that mean differences in intelligence between racial and ethnic groups are partially genetic. These lines of evidence are findings in support of Spearman’s hypothesis, consistent results from tests of measurement invariance across American racial groups, the mathematical relationship that exists for between-group and within-group sources of heritability, genomic data derived from genome-wide association studies of intelligence and polygenic scores applied to diverse samples, and admixture studies. I also discuss future potential lines of evidence regarding the causes of average group differences across racial groups. However, the data are not fully conclusive, and the exact degree to which genes influence intergroup mean differences in intelligence is not known. This discussion applies only to native English speakers born in the United States and not necessarily to any other human populations.

Race, Ethnicity, and the Scarr-Rowe Hypothesis: A Cautionary Example of Fringe Science Entering the Mainstream

In 2020, Pesta et al. published an article entitled "Racial and Ethnic Group Differences in the Heritability of Intelligence: A Systematic Review and Meta-Analysis" in the journal Intelligence. The authors framed their analysis as an examination of the Scarr-Rowe hypothesis, which holds that the heritability of intelligence varies as a function of socioeconomic status. Pesta et al. concluded that the heritability of intelligence does not differ across racial and ethnic groups in the United States. They claimed their results challenge the Scarr-Rowe hypothesis and support the hereditarian position that mean differences in IQ among racial and ethnic groups are attributable to genetic differences rather than environmental disparities. In this commentary, we outline severe theoretical, methodological, and rhetorical flaws in every step of Pesta et al.'s meta-analysis. The most reliable finding from Pesta et al. is consistent with the Scarr-Rowe hypothesis and directly contradicts a hereditarian understanding of group differences in intelligence. Finally, we suggest that Pesta et al. serves as an example of how racially motivated and poorly executed work can find its way into a mainstream scientific journal, underscoring the importance of robust peer review and rigorous editorial judgment in the open-science era.