---
title: "Race and intelligence"
chunk: 9/9
source: "https://en.wikipedia.org/wiki/Race_and_intelligence"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:18:16.114269+00:00"
instance: "kb-cron"
---

=== Racial admixture studies ===
Most people have ancestry from different geographical regions. In particular, African Americans typically have ancestors from both Africa and Europe, with, on average, 20% of their genome inherited from European ancestors. If racial IQ gaps have a partially genetic basis, one might expect black people with a higher degree of European ancestry to score higher on IQ tests than black people with less European ancestry, because the genes inherited from European ancestors would likely include some genes with a positive effect on IQ. Geneticist Alan Templeton has argued that an experiment based on the Mendelian "common garden" design, where specimens with different hybrid compositions are subjected to the same environmental influences, are the only way to definitively show a causal relation between genes and group differences in IQ. Summarizing the findings of admixture studies, he concludes that they have shown no significant correlation between any cognitive ability and the degree of African or European ancestry.
Studies have employed different ways of measuring or approximating relative degrees of ancestry from Africa and Europe. Some studies have used skin color as a measure, and others have used blood groups. Loehlin (2000) surveys the literature and argues that the blood groups studies may be seen as providing some support to the genetic hypothesis, even though the correlation between ancestry and IQ was quite low. He finds that studies by Eyferth (1961), Willerman, Naylor & Myrianthopoulos (1970) did not find a correlation between degree of African/European ancestry and IQ. The latter study did find a difference based on the race of the mother, with children of white mothers with black fathers scoring higher than children of black mothers and white fathers. Loehlin considers that such a finding is compatible with either a genetic or an environmental cause. All in all Loehlin finds admixture studies inconclusive and recommends more research.
Reviewing the evidence from admixture studies Hunt (2010) considers it to be inconclusive because of too many uncontrolled variables. Mackintosh (2011, p. 338) quotes a statement by Nisbett (2009) to the effect that admixture studies have not provided a shred of evidence in favor of a genetic basis for the IQ gap.

=== Mental chronometry ===

Mental chronometry measures the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response by the participant. These studies have shown inconsistent results when comparing black and white populations groups, with some studies showing whites outperforming blacks, and others showing blacks outperforming whites. 
Arthur Jensen argued that this reaction time (RT) is a measure of the speed and efficiency with which the brain processes information, and that scores on most types of RT tasks tend to correlate with scores on standard IQ tests as well as with g. Nisbett argues that some studies have found correlations closer to 0.2, and that a correlation is not always found. Nisbett points to the Jensen & Whang (1993) study in which a group of Chinese Americans had longer reaction times than a group of European Americans, despite having higher IQs. Nisbett also mentions findings in Flynn (1991) and Deary (2001) suggesting that movement time (the measure of how long it takes a person to move a finger after making the decision to do so) correlates with IQ just as strongly as reaction time, and that average movement time is faster for black people than for white people. Mackintosh (2011, p. 339) considers reaction time evidence unconvincing and comments that other cognitive tests that also correlate well with IQ show no disparity at all, for example the habituation/dishabituation test. He further comments that studies show that rhesus monkeys have shorter reaction times than American college students, suggesting that different reaction times may not tell us anything useful about intelligence.

=== Brain size ===

A number of studies have reported a moderate statistical correlation between differences in IQ and brain size between individuals in the same group. Some scholars have reported differences in average brain sizes between racial groups, although this is unlikely to be a good measure of IQ as brain size also differs between men and women, but without significant differences in IQ. At the same time newborn black children have the same average brain size as white children, suggesting that the difference in average size could be accounted for by differences in environment. Several environmental factors that reduce brain size have been demonstrated to disproportionately affect black children.

=== Archaeological data ===
Archaeological evidence does not support claims by Rushton and others that black people's cognitive ability was inferior to white people's during prehistoric times.

== Policy relevance and ethics ==

The ethics of research on race and intelligence has long been a subject of debate: in a 1996 report of the American Psychological Association; in guidelines proposed by Gray and Thompson and by Hunt and Carlson; and in two editorials in Nature in 2009 by Steven Rose and by Stephen J. Ceci and Wendy M. Williams.
Steven Rose maintains that the history of eugenics makes this field of research difficult to reconcile with current ethical standards for science.
On the other hand, James R. Flynn has argued that had there been a ban on research on possibly poorly conceived ideas, much valuable research on intelligence testing (including his own discovery of the Flynn effect) would not have occurred.
Many have argued for increased interventions in order to close the gaps. Flynn writes that "America will have to address all the aspects of black experience that are disadvantageous, beginning with the regeneration of inner city neighborhoods and their schools." Especially in developing nations, society has been urged to take on the prevention of cognitive impairment in children as a high priority. Possible preventable causes include malnutrition, infectious diseases such as meningitis, parasites, cerebral malaria, in utero drug and alcohol exposure, newborn asphyxia, low birth weight, head injuries, lead poisoning and endocrine disorders.

== See also ==
Behavioral epigenetics
Melanin theory
Model minority
Nations and IQ
Outline of human intelligence

== References ==

=== Notes ===

=== Citations ===

=== Bibliography ===