Robin was very impressed by Malcolm Gladwell's piece on IQ and the Flynn effect in The New Yorker. I wasn't; Gladwell leaves out a lot. (He also falsely attributes a bizarre view to Murray and Herrnstein, which the magazine has already had the grace to correct).
However, Gladwell does repeat two arguments that are persuasive, but don't really prove much. Lucky me: I've been waiting years for a chance to answer them!
If I.Q. is innate, it shouldn’t make a difference whether it’s a mixed-race child’s mother or father who is black. But it does: children with a white mother and a black father have an eight-point I.Q. advantage over those with a black mother and a white father.
The problem is that there is a simple genetic explanation: In all likelihood, the black man who marries a white woman will be above his group average in success and IQ; the white man who marries a black woman will be below his group average in success and IQ. You might see an offsetting effect in the women (i.e., white women who marry black men may be below their group average in success and IQ, black women who marry white men may be above their group average in success and IQ). But since men's prospects in the marriage market are much more heavily linked to success than women's, the offset will probably be modest.
This doesn't mean that the genetic explanation is right, just that the mixed-race IQ pattern Gladwell highlights does not distinguish between the environmental and genetic stories.
And it shouldn’t make much of a difference where a mixed-race child is born. But, again, it does: the children fathered by black American G.I.s in postwar Germany and brought up by their German mothers have the same I.Q.s as the children of white American G.I.s and German mothers.
The problem with this famous Eyferth study, which formed the backbone of Flynn's Race, IQ, and Jensen, is that it was a study of children. So? After Flynn wrote this book, behavioral geneticists gradually made the amazing discovery that the heritability of IQ (and many other traits) sharply rises as children grow up, while family effects on IQ fade out. The Eyferth results tip the scales modestly in an environmental direction, but primarily confirm what we already know: Children's environment has a substantial effect on their IQs when they are children. The truly probative study would have tested the IQs of the Eyferth subjects in adulthood. As far as I know that never happened, and now it's probably too late.
Again, none of this confirms the genetic explanation. My point is merely that a popular piece of counter-evidence is quite a bit weaker than it seems.