Related Experiment Video
Updated: May 18, 2026
09:13
Hypoxia Alters miRNAs Levels Involved in Non-Mendelian Inheritance of Autism Spectrum Disorder in Mice
Published on: July 11, 2025
No narrowing in mean Black-White IQ differences--predicted by heritable g
1Department of Psychology, University of Western Ontario, London, Ontario N6A BC2, Canada. rushton@uwo.ca
The American Psychologist
|September 12, 2012
Summary
This commentary argues that intelligence differences between Black and White individuals have not significantly narrowed, challenging previous claims. Genetic factors, not social influences, are presented as key to understanding these IQ disparities.
Area of Science:
- Psychology
- Behavioral Genetics
- Psychometrics
Background:
- Critiques Nisbett et al.'s (2011) assertion of a 5.5-point narrowing of the Black-White IQ gap between 1972-2002.
- Highlights overlooked objections from Rushton and Jensen (2006) and subsequent evidence regarding IQ gap trends.
- Addresses the role of heritability (g) in understanding racial differences in intelligence.
Purpose of the Study:
- To refute Nisbett et al.'s claims regarding the narrowing of the Black-White IQ gap.
- To re-evaluate the evidence for genetic contributions to intelligence differences between racial groups.
- To challenge the emphasis on environmental factors like age and social class interactions.
Main Methods:
- Re-analysis of existing data and literature on IQ differences.
- Critique of methodologies used in previous studies (e.g., adoption studies of young children).
- Emphasis on findings from twin and adoption studies concerning heritability of intelligence.
Main Results:
- Contends that the Black-White IQ gap has not significantly narrowed as previously claimed.
- Asserts that heritability estimates for intelligence are consistent across racial groups (White, Black, East Asian) by adolescence (approx. 50%).
- Finds no empirical support for unique cultural influences (deprivation, minority status) affecting intelligence in specific groups.
Conclusions:
- Nisbett et al. inaccurately represented the trends in the Black-White IQ gap and the role of genetics.
- Heritability of intelligence (g) provides a more accurate framework for understanding racial differences than environmental factors.
- Evidence suggests consistent genetic contributions to intelligence across diverse racial groups, refuting claims of significant cultural impact.
Related Concept Videos
01:30Biological Influences on Intelligence
Intelligence is often thought to be linked to brain size, but the relationship is more complex than that. While brain size does correlate modestly with some abilities, like verbal skills, the connection is weaker for others, such as spatial reasoning. Other factors, like brain structure, also play crucial roles. For instance, despite Einstein's smaller-than-average brain, his parietal cortex, which is involved in spatial reasoning, was 15% wider, suggesting that neural density might matter more...
01:06Heritability
Heritability is a statistical concept that measures the degree to which genetic differences among individuals contribute to trait variations within a population. It is a fundamental idea in genetics, often prone to misinterpretation. Heritability is expressed as a percentage, reflecting the proportion of variation in a specific trait across a population that can be linked to genetic differences. However, it's important to understand that heritability does not determine how "genetic" a trait is,...
01:29Environmental Influences on Intelligence
Despite the strong genetic influence on traits like intelligence, environmental factors significantly shape outcomes. For example, while over 90% of height variation is due to genetic differences, environmental factors such as nutrition also have a notable impact. Similarly, for intelligence, changes in a child's surroundings can significantly alter their IQ. Research shows that enriched environments boost children's academic success and help them develop key cognitive skills. Children from...
01:11Genetic Lingo
Overview
01:21The Bell Curve
The normal probability distribution, often depicted as a symmetrical, bell-shaped curve, is fundamental in statistics and the study of natural phenomena. This pattern, famously described by mathematician Carl Friedrich Gauss, shows how data points are distributed around a central mean, with most values near the average and fewer observations occurring as they deviate further from it.
This pattern applies to many human characteristics beyond intelligence, such as height. For example, if you...
This pattern applies to many human characteristics beyond intelligence, such as height. For example, if you...
01:18Polygenic Traits
When more than one gene is responsible for a given phenotype, the trait is considered polygenic. Human height is a polygenic trait. Studies have uncovered hundreds of loci that influence height, and there are believed to be many more. Due to the high number of genes involved, as well as environmental and nutritional factors, height varies significantly within a given population. The distribution of height forms a bell-shaped curve, with relatively few individuals in the population at the...