Avery Tooley has posted a response to an argument that the high incidence of low birth weight among black Americans is a sign that slavery's legacy still has a biological impact. There are places the argument isn't careful enough. Avery points out one. It would be more helpful to figure out what's different between cases of blacks with low birth weight and blacks with more normal birth weight than simply to notice a difference on average between blacks and whites. The details of the particular cases might make all the difference.
But there are other problems with the argument also. [What follows comes from a comment I left on Avery's post.] They notice that blacks in the U.S. have lower birth weight than blacks born in Africa living in the U.S. But that's the same comparison used in the IQ debate, and it's still a debated comparison. Thomas Sowell, John McWhorter, and others cite it to show that black kids in the U.S. don't have as high a cultural expectation to develop their natural potential in certain kinds of intelligence. But those on the other side of the issue point out that the immigrants to the U.S. are self-selecting. They're more inclined to be smarter and harder-working to begin with. Perhaps they're more inclined to be healthier too, since healthier people are more likely to be positive and looking to improve their lot in life. Perhaps.
Where that response fails with IQ is that second-generation studies show that the drive to do well falls rapidly among immigrants' children and especially grandchildren if the children weren't themselves born here). That means it's cultural in some way, but that cultural impact could be because racism gets them down, from cultural opposition to acting white, or some combination of those and maybe other things too. But it's clearly not entirely a biological thing, even one resulting from the effects of slavery. So the question is whether birth weight falls rapidly in the second generation of black immigrants. Then we'd have some sense of whether it's a biological effect that continues to the next generation or a cultural effect, which could again have several explanations, perhaps many of which contribute to a larger story. I'd have to say that I'm skeptical of this proposed biological effect myself.