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Race and Intelligence

Genes and intelligence: a clear verdict, Race and IQ: not so clear

Throughout human history, people have tended to divide each other into groups. Most often, physical characteristics are used to distinguish between groups, and the groups are called races. Some people have long believed that many characteristics about a person could be determined by simply looking at the person's race. Intelligence is one trait that has been studied in an attempt to correlate it to racial groups. In fact, at present the best evidence does not strongly support the idea that the people of any race are more or less intelligent than those of any other race. In addition, intelligence testing is an imperfect science. Traditional tests are skewed to favor certain segments of society.

Genes and intelligence: a clear verdict

Saying that intelligence is partly genetic—programmed in the genes and inherited from one generation to the next—is vastly different than saying that genes underlie any racial differences. To give a classic example, scatter two identical groups of seed on a rich and a barren, dry plot of land. Within the rich plot, genetics will determine any difference in seed growth. But environment will cause most of the difference between the two plots.

Studies estimate that genes account for between 30 and 80% of our intelligence. Using meta-analysis—a statistical method that allows researchers to compare data from different experiments—a group of researchers showed that, when all these studies are taken together, genetics appear to determine roughly half of intelligence, environment the other half. Interestingly, the meta-analysis also suggested that pre-birth environmental factors such as the mother's nutrition, which are difficult to measure in any study, might underlie most of the environmental difference.

These results make some common sense. We know that intelligent people tend to have intelligent children— but not always. Some studies have also suggested that intensive programs may make a large difference in disadvantaged children's intelligence quotient (IQ) scores.

The problem with this split is that unrecognized differences in either genetic inheritance or environment might skew otherwise carefully crafted studies of race and intelligence. This problem will haunt nearly every single study we discuss.

Race and IQ: not so clear

The question of whether human races possess different intellectual capacities comes, at least in part, from an early twentieth-century observation that African Americans' IQ scores were, on the average, 15 points lower than those of white Americans. Recently, the black/white IQ difference has decreased; today it's closer to 10 points.

It's difficult to see how a five-point change in the IQ difference between black and white Americans could have come about in less than a century if genetics caused the difference entirely. Even more interesting, Americans and western Europeans today score 15 points higher on identical IQ tests than their great-grandparents did. A 15-point difference in IQ is significant (an IQ of 100 is "average," 130 "gifted"); but we clearly aren't more intelligent than our great-grandparents. It seems that environmental factors can and do play havoc with our attempts to measure intelligence.

A number of researchers have undertaken studies to uncover the source of the 10-point IQ difference between the races. One type of study measures the IQs of children of different racial backgrounds who are raised in similar environments. African Americans, on the average, have 70% African and 30% European ancestry. If whites were genetically more intelligent than blacks, we would expect black children with more European ancestry to have higher IQs than those with more African ancestry, even when they're raised in the same family.

Psychologists have used three ways to estimate white ancestry in African Americans. (It is worth noting that there are no "pure" racial groups.) Skin color is an imperfect measure, because not all native African peoples have dark skin. Also, children with lighter skin may be treated differently, even in the same family. Family histories of white ancestry may or may not be accurate. Possibly the best method tests blood groups; different racial groups have different rates of certain blood groups, allowing one to make a statistical estimate of ancestry.

The results of these studies suggest little, if any, intelligence difference between the races. The skin-color studies do tend to show a slight advantage for lighterskinned children—with all the reservations about children with lighter skin getting different treatment. But family history and blood group studies show no difference in IQ, apart from the skin-color effect.

Another approach to these studies measures the IQs of black children brought up in white families. In one study of black, interracial, and white adopted children raised in white families, the white children showed the highest IQ scores, with interracial children scoring in the middle. But it's not clear whether the white families treated the black children differently; whether the black children had suffered from IQ-reducing environments before they were born; or whether the older average age of adoption for the black children in the study prevented a fair comparison.

Another study, of black West Indian (Caribbean) children and English children raised in an orphanage in England, found that the Caribbean children had higher IQs than those from England, with mixed-race children scoring in between. But were the black children given more attention by orphanage staff? Were particularly intelligent Caribbeans emigrating to England for better economic opportunity?

Finally, a study of black children adopted by white versus black families in America showed that the black children raised by whites had higher IQ scores than those raised by blacks—suggesting an environmental cause. When the studies are taken together, the many caveats involved with the role of genetics and environment make it hard to draw firm conclusions. But the balance of data suggests no racial difference in intelligence.

See also Intelligence quotient; Culture-fair test

Kenneth B. Chiacchia

Further Reading

Devlin, B., Michael Daniels, and Kathryn Roeder. "The Heritability of IQ." Nature 388 (1997): 468-71.

Holloway, Marguerite. "Flynn's Effect." Scientific American (January 1999).

Jencks, Christopher and Meredith Phillips, eds. The Black-White Test Score Gap. Washington, D.C.: Brookings Institution Press, 1998.

McGue, Matt. "The Democracy of the Genes." Nature 388 (1997): 417-18.

Plomin, Robert. "Genetics and General Cognitive Ability." Nature 402 (supplement) (1999): C25-C29.

Plomin, Robert and Stephen A. Petrill. "Genetics and Intelligence: What's New?" Intelligence 24, no. 1 (1997): 53-77.

Wickelgren, Ingrid. "Nurture Helps Mold Able Minds." Science 283, no. 5409 (1999): 1832-834.

Additional topics

Psychology EncyclopediaPsychological Dictionary: Perception: early Greek theories to Zombie