More than four decades ago, a psychologist’s landmark idea linked family income with children’s cognitive abilities. Now, new findings by a group that includes a University of Florida Health researcher show no evidence for that theory.

“While children from higher socioeconomic status backgrounds have much better cognitive outcomes on average than do those from lower socioeconomic status backgrounds, genetics appears to matter just as much for both groups,” said David Figlio, PhD, dean of the Northwestern University School of Education and Social Policy, the primary author of the study and a former UF economics professor. “Genes matter. Environment matters. But we find no evidence that the two interact.”

In the largest and most diverse study of its kind, the researchers analyzed birth and school records from more than 24,000 twins and nearly 275,000 siblings in Florida. They analyzed math and reading test scores for children in the third through eighth grades who were born between 1994 and 2002.

They found the children’s socioeconomic status was unrelated to the genetic influences that drive cognition and test scores, according to a new study published in the Proceedings of the National Academy of Sciences journal. Cognitive abilities are the brain-based skills used to perform mental tasks, pay attention and communicate. The study focused on twins because they allow researchers to disentangle the role of genes and environment in development.

“There’s been an idea that genetic influences on cognitive development are more important for kids from rich families than kids from poor families. This has been based on studies using twins. We looked at the question using far more twins than anyone else has, and we don’t find any evidence for this idea,” said Jeremy Freese, PhD, a Stanford University sociology professor and primary author of the study.

Jeffrey Roth, PhD, a research professor emeritus in the UF College of Medicine’s department of pediatrics who collaborated on the research, said parents who stayed in school longer are still likelier to have higher-performing children. However, the findings suggest that understanding the gene-environment interaction that ultimately influences children’s cognitive abilities is far more complex and elusive than originally thought.

One particularly encouraging aspect of the findings is that children who are born into modest family circumstances are not presumed to be at a disadvantage for cognitive development, Roth said.

“We did not find that poor environments alone are more harmful to children’s cognitive abilities than a privileged environment,” Roth said.

Renowned psychologist Sandra Wood Scarr’s original 1971 idea that genetic influences on intellectual development differed by socioeconomic status was reaffirmed by David Rowe in 1999 and has been supported by other findings. Other reviews of the so-called Scarr-Rowe interaction have been less conclusive, including inconsistent results and only modest support, especially in non-U.S. settings.

More work is needed to reveal the useful ways that genetic differences matter in cognitive development, said Freese, the Stanford researcher.

“We know poor children face many social disadvantages and there is much we can do to address those to help promote the flourishing of all children,” he said.

In the future, Roth said it may be possible to better understand the gene-environment interaction by using molecular genetic data rather than by simply observing the cognitive abilities of twins in rich and poor families.

“There’s the potential for better predictions about cognitive development if we know the genetic makeup of individuals,” he said.