Scientists have achieved a breakthrough in deciphering the genetics of intelligence. Ironically, they did it by accounting for a key environmental factor.
Breast-feeding boosts children’s IQs by 6 to 7 points over the IQs of kids who weren’t breast-fed, but only if the breast-fed youngsters have inherited a gene variant associated with enhanced chemical processing of mothers’ milk, reports a team led by psychologist Avshalom Caspi of King’s College London.
The new finding supports the controversial hypothesis that fatty acids in breast milk enhance newborn babies’ brain development. Moreover, the results demonstrate that intelligence researchers must examine how children’s genetic natures interact with the ways in which they’re nurtured.
“Genes work via specific environmental experiences to shape intellectual development,” Caspi says.
He and his colleagues present their data in an upcoming Proceedings of the National Academy of Sciences.
Two groups of children participated in the study: 1,037 boys and girls born 34 to 35 years ago in New Zealand, who are still living there; and 2,232 boys and girls born 12 to 13 years ago who are growing up in England.
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In DNA isolated from blood samples, the researchers probed the gene fatty acid desaturase 2, or FADS2. This gene assists in breaking down fatty acids present in human milk. FADS2 comes in two forms, one of which enables the body to process fatty acids more efficiently than the other does.
Only breast-fed children who carried one or two copies of the more efficient gene displayed an IQ advantage.
In the two groups of children, 90 percent of youngsters possessed the critical FADS2 gene variant. Roughly half of all participants were breast-fed regularly during infancy, according to reports collected from the mothers when their children were 1 to 3 years old. The formula-fed infants typically received no fatty acids in their diets.
The New Zealand children completed standard IQ tests at ages 7, 9, 11, and 13. The British children took an IQ test at age five.
The scientists ruled out several alternative explanations of the findings. For instance, normal- and low-birth-weight babies carrying the critical FADS2 gene displayed equal IQ hikes when breast-fed. The same held for children from wealthy and poor families, and for kids with high-IQ and low-IQ mothers.
Also, no evidence indicated that mothers carrying the more efficient FADS2 gene produced better-quality milk or breast-fed more often than mothers carrying the other gene variant did.
Until now, researchers have largely failed in attempts to find genes that affect intelligence independently of environmental factors, Caspi says. However, a new genomewide analysis of more than 10,000 7-year-olds tagged six regions as weakly but significantly associated with IQ, including one on FADS3, another fatty acid gene. That study, directed by King’s College psychologist Lee M. Butcher, appears online Nov. 2 in Genes, Brain and Behavior.
“Both of these new findings suggest an important role for the regulatory mechanism of dietary fatty acids and its possible interaction with environmental factors in intelligence,” remarks biological psychologist Danielle Posthuma of the Free University of Amsterdam.
Adds psychologist Jeremy R. Gray of Yale University, “An IQ advantage of 6 to 7 points is unquestionably large enough to have a real-world impact on individuals.”