From Nature:
Does breast-feeding a child boost its brain development and raise its intelligence? Only if the child carries a version of a gene that can harness the goodness of breast-milk, say researchers. The results add to the ‘nature versus nurture’ debate over intelligence, by showing how the two effects can interact. The question of whether people are born intelligent or made intelligent by their environment has been debated for decades. Research with identical twins separated at birth has shown that both genetics and rearing conditions are important in determining intelligence.
One of the important environmental effects seems to be breast-feeding. Children who are breast-fed generally perform better in IQ tests than do those fed on other types of milk. Researchers think that this might be because specific fatty acids found in human milk, but not in cow’s milk or infant formulas, improve brain development. Avshalom Caspi and Terrie Moffitt, psychologists at King’s College, London, and their colleagues looked at the relationship between breast-feeding and intelligence to explore the possibility that in this case nature and nurture might be intimately linked.
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