2. The question of Occam's Razor is quite interesting. Now both D'Souza and Jensen argue that by Occam's Razor, the postulate of deep heritable racial differences is the simplest hypothesis to account for the persistence of the one standard deviation gap in black/white test scores and thus to be preferred. On this ground they argue against the more "complex" interactive effects of contemporary racism, history and socio economic status. But what is Occam's Razor? Occam famously argued that "one should not needlessly increase the number of abstract entities." He did not so much argue for simple over complex explanations. That is, Occam was a nominalist who held that there were only singular individuals and that words designating a group of individuals or a concept were useful conventions, but did not designate a reality and were therefore to be mistrusted. Now given everything we know about polymorphic variation, Occam's Razor means we should be quite skeptical of the concept of race as a real biological entity.
So I agree with the following and underline once again that the Bell Curve does not recognize such arguments, even for the point of refutation. For a simple development of what you are getting at for those who want to follow up, see Richard Lewontin, Human Diversity; John VanderMeer Reconstructing Biology; Jonathan Marks, Human BioDiversity. .These are all first year college level biology/genetics texts
>Race is, for scientific purposes, an arbitrary categorization.
>Even diseases that are tied to race have nothing to do with race and
>everything to do with place. Genetically isolated populations develop
>genetic disease. Thus sickle-cell anemia is not a disease of black
>people, but a disease which developed in an isolated population that
>happened to be black and happened to be from the area where African slaves
>were taken. There is no reason to believe and every reason to disbelieve
>that American blacks are a genetically isolated population to an extent
>that they would show a consistent divergence in brain function and
>certainly not to the extent that Murray demonstrates. He's cut his own
>throat and he's too stupid to see it.
3. As for identical twins raised together, what most studies miss is not only the similar external environment they share but also the interactive, mirroring effect they have on each other.. As for identical twins raised apart, this turns out not to have been the case in many instances; they were raised by different aunts or uncles or whatever. At any rate, whatever intra group variation is heritable does not mean of course that inter group variation is heritable. Jensen did not understand that originally but now everyone does.
best, rakesh