Nature Via Nurture
Studies have shown that the IQs of breastfed children are, on average, about 6 points higher than those given baby formulas.
Terrie Moffitt and Avshalom Caspi suspected the involvement of a gene called FADS2, which regulates the metabolism of long-chain polyunsaturated fatty acids — which are important for the growth of nerve cells and are abundant in human milk. FADS2 comes in two varieties, known as C and G, and the researchers wondered if these two varieties interacted differently with breast milk.
To find out (see “Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism“), they drew on data from two groups of people, one in New Zealand (born in 1972 and 1973) and one in Britain (born in 1994 and 1995).
The researchers found that the increase in intelligence associated with breastfeeding only happened to people who had inherited at least one copy of the C version of FADS2. (Most genes are present as two copies, one inherited from the mother and one from the father.) The effect did not depend on parental social class or IQ, nor on birthweight (low birthweight has been linked to lower IQ). And the difference in IQ was preserved into adulthood.
Only about 10% of the population is double-G.