Are Racial Disparities in IQ Primarily Genetic? An Analysis of Scholarly Research

Racial differences in intelligence have been a subject of debate and research for decades. Many studies suggest that these differences may be partly hereditary, and this article aims to analyze some of the key findings from influential works including “The Bell Curve” by Charles Murray, “Thirty Years of Research on Race Differences in Cognitive Ability” by Arthur Jensen and Philippe Rushton, and recent studies on psychometric g.

Psychometric g and Its Heritability

Psychometric g, or general intelligence, is a measurement of overall cognitive ability. Several studies have found that psychometric g is highly heritable, with up to 91% of its variance being heritable (Kirkegaard et al., 2019).

When two breeding groups mix, the resulting hybrid group shows IQs that are positively correlated with the admixture at the individual level. This suggests that genetic factors play a significant role in determining differences in cognitive ability between racial groups.

The Role of Genetics in Intelligence

Intelligence is largely determined by the DNA we inherit from our parents. However, environmental factors such as disease, toxins, and head trauma can also influence cognitive function. According to recent research, there are tens of thousands of single nucleotide polymorphisms (SNPs) within an individual’s DNA that contribute to cognitive abilities, each with an average effect size of only 0.01. In total, there are approximately 4 to 5 million SNPs in a person's genome, and millions more have been identified in populations around the world (Kirkegaard et al., 2019).

Research Evidence: The Bell Curve and Beyond

The Bell Curve by Charles Murray (1994) and Thirty Years of Research on Race Differences in Cognitive Ability by Arthur Jensen and Philippe Rushton (2005) are seminal works in the study of racial disparities in intelligence. Murray's book, though often controversial, is noted for its thorough and scientifically grounded analysis. As Jensen and Rushton point out, many of the points made in the book remain credible even after several decades (Murray, 2021).

The book The Bell Curve carefully examines the evidence for genetic differences in intelligence. While it is widely debated, the core findings of the book regarding the significant role of genetics in cognitive ability are still valid today. For those interested in a detailed exploration of these issues, Murray's recent work Facing Reality is highly recommended (Murray, 2021).

Arthur Jensen and Philippe Rushton summarize decades of research on race differences in cognitive ability in their work, Thirty Years of Research. This summary highlights the substantial and consistent evidence supporting the genetic basis of intelligence differences between breeding groups. Their work confirms Spearman’s hypothesis, which posits that racial differences in intelligence are differences in the general factor of cognitive ability (g). This hypothesis has been repeatedly confirmed in studies comparing test scores across populations (Spearman, 1927).

Specifically, when a group with a low mean IQ is tested with a culture-loaded test and a culture-free test, they tend to perform better on the culture-loaded test. This indicates that cultural factors may influence test performance, but the culture-free tests are more heavily weighted towards the g factor, which is thought to be more heritable (Jensen Rushton, 2005).

Personal Insights and Conclusions

As someone who has interacted with researchers such as Jensen and Rushton, and who continues to engage with the work of Charles Murray, I have gained a deeper understanding of the complexities involved in this field. While the debate over racial disparities in IQ remains intense, the body of evidence supporting a genetic component to these differences is substantial.

This research underscores the importance of considering both genetic and environmental factors in the study of cognitive abilities. It also highlights the need for ongoing scientific investigation to better understand the multifaceted nature of intelligence across different populations.

References:

Kirkegaard, E. O. W., Woodley of Menie, M. A., Williams, R. L., Fuerst, J., Meisenberg, G. (2019). Biogeographic Ancestry, Cognitive Ability, and Socioeconomic Outcomes. Psych, 11(1), 1-25. Herrnstein, R. J., Murray, C. (1994). The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press. Murray, C. (2021). Facing Reality. Encounter Books. Rushton, J. P., Jensen, A. R. (2005). Thirty Years of Research on Race Differences in Cognitive Ability. Psychology, Public Policy, and Law, 11(2), 235-294. Spearman, C. (1927). The ability factor in anthropometric and intelligence tests. American Journal of Psychology, 38(3), 264-276.