A new study examines how genes and environment both play a critical role in shaping an individual's intelligence. The findings are published in the journal Psychological Science.
However, researchers found that the influences of genes on intelligence varied based on people's social class in the United States, but not in Western Europe or Australia.
"The hypothesis that the genetic influence on intelligence depends on socioeconomic status was not supported in studies outside of the US," said Elliot Tucker-Drob of the University of Texas at Austin, in a news release. "In the Netherlands, there was even evidence suggestive of the opposite effect."
During the study, researchers conducted a meta-analysis that combines data from both published and unpublished studies containing an objective measure of intelligence that measured participants' family socioeconomic status during childhood. The studies also had to include participants that varied in their genetic relatedness (i.e., siblings versus identical twins) so that the researchers would be able to statistically disentangle genetic and environmental influences.
They analyzed data from a total of 24,926 pairs of twins and siblings who participated in the studies conducted in the United States, Australia, England, Germany, Sweden and the Netherlands--showing that the relationship between genes, intelligence and socioeconomic status really depended on which country the participants came from.
Furthermore, the meta-analysis did not show signs that other factors, including age of testing, whether the tests were of a single ability or composite cognitive measures, whether the tests measured achievement or knowledge of intelligence influenced the results.
Researchers believe that the study results could potentially be explained by the difference between the United States and other countries' differences in how low socioeconomic status is experienced in the areas.
In the future, researchers hope to identify certain 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," he concluded.
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