Not all children can harness the full goodness of their mother’s milk. 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...