CHICAGO: Scientists have identified a gene which leads children to have higher IQs if they are breastfed, a study said.

The study, released on Monday, took a bite out of the nature versus nurture debate by showing that intellectual development is influenced by both environmental and genetic factors.

"There has been some criticism of earlier studies about breastfeeding and IQ that they didn't control for socioeconomic status, or the mother's IQ or other factors," said study co-author Terrie Moffitt, a professor of psychological and brain sciences at Duke University and King's College in London.

"Our findings take an end-run around those arguments by showing the physiological mechanism that accounts for the difference."

Researchers examined more than 3,000 breast-fed infants in Britain and New Zealand and found that the child's IQ was an average of 6.8 points higher if the child had a particular version of a gene called FADS2.

This difference remained after researchers were able to rule out the influence of socioeconomic status, the IQ scores of the mother, birth weight and gestational age as factors.

"The argument about intelligence has been about nature versus nurture for at least a century," Moffitt said. "We're finding that nature and nurture work together."

Ninety per cent of the children had at least one copy of version of the gene which yielded higher IQ if they were breast-fed.