College of Liberal Arts

Genetic Potential for Intelligence Adversely Affected by Social Class in U.S. only

Fri, Dec 18, 2015
Photo by cybrarian77, Flickr.
Photo by cybrarian77, Flickr.

Genetic influence on intelligence varies according to people’s social class in the United States, but not in Western Europe or Australia, according to a psychology study at The University of Texas at Austin. 

Research suggests that genes and environment both play critical roles in shaping a person’s intelligence. A longstanding hypothesis in the field of behavioral genetics holds that a person’s potential intelligence, as set by genetics, is more fully expressed in environments that are supportive and nurturing, but is suppressed in conditions of poverty and disadvantages.

That hypothesis holds true only in the U.S., according to research that combines data from 14 independent studies in the United States, Australia, England, Sweden, Germany and the Netherlands.

To better understand the impact of social class on the link between genes and intelligence, UT Austin associate professor of psychology Elliot Tucker-Drob and University of Edinburgh psychology professor Timothy Bates analyzed data from 24,926 pairs of twins and siblings, finding that the relationship between genes, socioeconomic status and intelligence depended on which country the participants were from.

“Genetic influences on intelligence were stronger for Americans raised in higher socioeconomic status circumstances. For Americans raised under impoverished circumstances, genetic influences on intelligence were weaker,” said lead author Tucker-Drob, a research associate in the UT Austin Population Research Center. “There was no evidence for such a gene-by-environment interaction in studies from Western Europe and Australia. Those studies indicated that genetic influences on intelligence were constant across levels socioeconomic status.”

The researchers found that other factors — such as age of testing, whether the tests measured achievement and knowledge or intelligence, or whether the tests were of a single ability or a composite of cognitive measures — influenced the results.

“We believe that one possible factor contributing to the differences observed may be the quality of the social safety net,” says Tucker-Drob, suggesting that the differences may lie in how low socioeconomic status is experienced in each country. That is, the relatively robust social welfare programs in Western Europe and Australia may buffer the suppressive effects of environmental privation on genetic influences on intelligence, Tucker-Drob said.

Bates suggested that future research should identify the specific aspects of a society that “break the link between social class and the expression of genetic potentials for intellectual development.”

“Once such characteristics are identified, they could inform policies directed at narrowing test score gaps and promoting all of the positive consequences of higher IQ, such as health, wealth, and progress in science, art and technology,” said Bates.

The Population Research Center is supported by National Institutes of Health Grant No. R24HD042849. Portions of this article were prepared while Tucker-Drob was supported as a Visiting Scholar at the Russell Sage Foundation. The findings are published in Psychological Science, a journal of the Association for Psychological Science.

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