In “The nature of nurture” (Science and Technology November 10th 2007) you state:
“Making stupid comments about the second question (racial differences in intelligence) can be a career-killing move, as James Watson, a co-discoverer of the structure of DNA, recently found. He suggested that he was “inherently gloomy about the prospect of Africa” because “all our social policies are based on the fact that their intelligence is the same as ours [presumably he meant white people]—whereas all the testing says not really”. Such remarks are not merely offensive, they are scientifically weird. If the term race has any useful scientific meaning, then Africa, the continent where modern humanity began, is the most racially diverse place on the planet.”
On this argument there could only be dark-skinned humans on the planet, as there are no light-skinned Africans. The mistake is to ignore adaptations subsequently forced on those early humans who left Africa to colonise colder climates, whose descendants survived the ice ages. The existence of adaptations in physiology, intelligence, and/or personality traits in non-African populations is a matter for empirical research, not an eventuality ruled out in principle.
Later in the article you state “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. It is a nice irony, given the traditional association of the naturist position with eugenic arguments, that if variation in intelligence really is caused by underlying genetic variation, then the dull are as evolutionarily fit as the clever. But that is the logical conclusion.”
In fact it is quite unusual for environmental selection to create a completely uniform genotype, especially when the trait is as complex as intelligence. One might as well wonder why human beings are not all exactly the same height genetically, with all variance being down to ‘nurture’ (e.g. diet).
IQ measurements are standardised on European populations with mean 100 and standard deviation 15. This means that 68% of the population will lie between IQ 85 and IQ 115. In this context the 6 IQ points difference found in the differing genetic response to breastfeeding is well within average.
NOTE (Nov. 14th 07): I doubt the short version of this letter I did actually submit to The Economist will be published, but I received a friendly letter from their science editor conceding I was correct.