Did Bell actually specifically claim those things, or is this some reviewers "interpretation" of what he said?? IMO, a low IQ can also cause low income, low job performance, pregnancy out of wedlock, etc., etc. Chicken?? Or egg??
If I remember correctly, Murray and Herrnstein’s conclusion was that social welfare programs to “fix” problems of education levels or socio-economic status in “under-privileged” communities were not successful. The Great Society was inherently flawed because social engineering did not lead to improved individual outcomes in terms of income, job performance, pregnancy out of wedlock, and crime.
What mattered, statistically, was IQ. Which is much harder to “fix”. People with lower IQs tended to have bad outcomes in terms of income, job performance, pregnancy out of wedlock, and crime.
Murray and Herrnstein were pretty careful to say that this was not a skin problem. It’s not really race. It’s an IQ problem. But, all studies agree that there are racial disparities when it comes to IQ. And so there is a tie between these things. But social engineering won’t fix anything.