"The Bell Curve" is full of $h!t. There's nothing wrong with black Americans that can't be attributed to one form or other of cultural malaise, or to lower levels of prenatal and early childhood nutrition, possibly including a lower incidence of breastfeeding among many black mothers.
IMHO *all* of the "bell curve" difference is resolvable if the right cultural factors and expectations were changed.
Genetic differences between races are small compared with the genetic differences between one individual and the next, even when the individuals compared are of the same race.