New research finds that a disadvantaged environment can prevent genetics from doing its job.
The strong new analysis published in the journal Psychological Science suggests that the role of genetics in intelligence indeed varies with socioeconomic status, reports an article on citylab.com.
The findings are just the latest scientific insight into how poverty alters the brain. Lab and field tests have found that scarcity imposes huge strains on mental resources, measured at a drop of 13 IQ points. Imaging studies, meanwhile, have revealed a link between income and the surface area of neural regions related to language and executive functioning in children. The new work tracks longer-term influences—but reaches similarly disturbing conclusions.
For this research, psychologist Elliot Tucker-Drob of the University of Texas at Austin and the paper’s lead author and the psychologist Timothy Bates of the University of Edinburgh in Scotland, identified 14 of the most reliable studies ever conducted on the role of nature and nurture on intelligence—eight from the U.S., and six from other countries. Altogether the data set comprised nearly 25,000 pairs of twins or siblings, for roughly 50,000 total individuals. This sort of meta-analysis heightens the statistical power of the research, lending more confidence to its conclusions.
In the American samples, Tucker-Drob and Bates found a significant “gene-by-socioeconomic status” effect—meaning the genetic influence on IQ scores and achievement varied with social class.
In the non-U.S. samples, the researchers found no significant interaction between genes and socioeconomic status for intelligence outcomes. (They actually reached a conclusion opposite to that of the US in the Netherlands.) The source of the geographical gap might come down to the different types of social programs employed in the US and other parts of the world—specifically those related to literacy, school quality, medical access, income, and upward mobility.
“The differences observed across nations might be explained by weaker social safety nets in the US compared to western Europe and Australia,” says Tucker-Drob.
“The results suggest that large-scale genetically informed research that incorporates careful measurement and consideration of both proximal and national social factors may provide a unique key to understanding the impact of specific policies on individual differences in intellectual development and academic achievement.”
The US finding, resolves an important debate in particular, according to the researchers. It held up to several potential moderating factors, such as childhood age, various measures of socioeconomic status, and single-versus-composite measures of cognitive ability.
One thing the study could not determine was whether race, which overlaps considerably with poverty in the US, played a role in the findings. But Tucker-Drob says he believes the results reflect social disadvantage, not race or ethnicity, because previous work has reached similar conclusions in “racially homogenous samples.” In other words, even when race is held constant, being poor seems to stifle genetic variation on intelligence.
