(NaturalNews) Babies who are breastfed have higher IQs than babies who are not -- but only if they contain a specific genetic marker, according to a study led by researchers at the King's College London Institute of Psychiatry and published in the "Proceedings of the National Academy of Science USA."
Researchers examined data on 1,000 children from New Zealand in the early 1970s and 2,000 children from the United Kingdom in the mid-1990s.
"Those who were breastfed scored on average three points above the population mean of 100 on the IQ test, whereas those who were not breastfed scored about three points below the population mean," co-author Terrie Moffitt said.
An IQ of 100 is defined as the population mean, or the hypothetical average of all IQ scores. Because of the relative nature of IQ scores, a potentially more accurate comparison is to say that breastfed children scored approximately six points higher on IQ tests than formula-fed children.
But this correlation only held true for the 90 percent of babies with at least one copy of the more common allele (version) of the gene "fatty acid desaturase 2 (FADS2)."
Among the children participating in the study, 50 percent carried two copies of the more common FADS2 allele, while 40 percent had two copies. Ten percent had no copies. Among the latter group, there was no correlation between breastfeeding and IQ.
According to education professor Linda Gottfredson of the University of Delaware, the study shows that it is not possible to identify human traits as solely the part of "genetics" or "the environment."
"[Genes] are more like playbooks," she said. "It's not nature or nurture, but your genes operate frequently by making you more susceptible or less susceptible to certain environmental conditions."
The mechanism by which breastfeeding and FADS2 might interact to affect IQ remains unknown.