> the Flynn effect changes the absolute scores, but not the difference.

I'm going to go out on a limb and suggest that if a test indicates that me and my fellow white English thirtysomethings produce average scores a standard deviation ahead of (i) thirtysomething black people living in my country and (ii) my white grandparents' generation when they were my age, what's actually measured by the observed one standard deviation average differences across cohorts probably isn't genetic differences....