From a response to a different attack on Lynn and Vanhanen:

Right. As I pointed out in my VDARE.com review in 2002, Lynn and Vanhanen's finding of an average IQ of 70 in black Africa is strong evidence in favor of the nurture position that a better environment can raise IQs, because African Americans, who appear to be about 4/5th black, score 15 points higher.

. . .

Moreover, there are still some low-hanging fruits where 3rd World countries would benefit from public health programs that succeeded in the U.S. in the first half of the 20th Century in boosting IQ directly or or in boosting mental energy. Fortifying salt with iodine eliminated the medical syndrome cretinism. while fortifying wheat with iron also eliminated an IQ-sapping medical condition. The Rockefeller Foundation's war on hookwarm greatly benefited the physical and economic energy of Southerners by ridding them of a parasite.