The Unrepentant Individual

...just hanging around until Dec 21, 2012

November 11, 2007

Breastfeeding And Evolution

Intelligence is not the most understood of human attributes, and is quite certainly one of the most contentious, especially when the field of genetics become involved.

Breastfeeding has been shown in some studies to be correlated with higher intelligence. But a recent study, reports The Economist, suggests that there is a genetic component as well. But here is where the story gets strange:

Dr Caspi and Dr Moffitt, however, were not so sure. They suspected the involvement of a gene called FADS2. This regulates the metabolism of a group of molecules called long-chain polyunsaturated fatty acids. These are important for the growth of nerve cells and are abundant in human milk but generally absent from formulas. FADS2 comes in two varieties, known as C and G, and the researchers wondered if these two varieties interacted differently with breast milk.

What Dr Caspi and Dr Moffitt found was 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 the social classes or IQs of the parents, nor on the birthweight of the child in question (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, but what is curious about this result is that the G version of the gene has survived at all. If intelligence is valuable, the C version might be expected to have become universal. Indeed, this is the nub of the nurturists’ argument. Natural selection should have pushed intelligence genes as far as they will go, so all variation should be environmental. That it is not suggests there is some unknown countervailing advantage—at least in reproductive terms—to being less than averagely bright.

This is incorrect. That the gene has not disappeared does not show that there is an advantage evolutionary to being dull, only that being dull isn’t a disadvantage to mating. Evolution is not necessarily based on what is optimal, only what is “good enough” to find a mate. I’d say that looks and pheromones are probably much more important traits than pure intelligence. After all, Britney Spears was able to reproduce twice, and nobody will say it was her brainpower that got her knocked up!

PS – I wonder what sort of Google hits this title will bring in!

Posted By: Brad Warbiany @ 7:03 pm || Permalink || Comments (2) || Trackback URL || Categories: Baby, News, Science


  1. That the gene has not disappeared does not show that there is an advantage evolutionary to being dull, only that being dull isn’t a disadvantage to mating.

    First off, evolutionary advantages are, by definition, advantages to mating, while evolutionary disadvantages are disadvantages to mating. That’s how evolution works.

    Secondly, I think it’s well-established that there *is* an evolutionary advantage to intelligence–and therefore it would be reasonable to surmise, for instance, that since these particular intelligence-linked genes have not won out, there must be another factor working the other way.

    Comment by Phil Welch — November 11, 2007 @ 7:34 pm
  2. One way or the other, breast feeding is better for the baby, and the mother, than bottle feeding.

    Comment by Lucy Stern — November 13, 2007 @ 8:09 pm

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