Thomas Sowell, “New Light on Black I.Q.” New York Times Magazine, March 27, 1977, pp. 57ff
James R. Flynn, “Mean IQ of Americans: Massive Gains 1932 to 1978” Psychological Bulletin 95 (1984): 29-51.
“Massive IQ Gains in 14 Nations” Psychological Bulletin 101 (1987): 171-91.
Eka Roivainen,“Economic, educational, and IQ gains in eastern Germany 1990-2006” Intelligence 40 (2012): 571-75.
William T. Dickens & James R. Flynn, “Black Americans Reduce the Racial IQ Gap: Evidence from Standardization Samples” Psychological Science, October 2006.
I have come to believe that it is not so simple as IQ, although IQ plays a major part.
It is certainly not a black/white issue, either. One of the authors noted the Ashkenazi Jews were the most highly rated group, followed by East Asians, as noted in the book. The evidence certainly seems to support the hypothesis.
Of course, the next question is, is it genetics or environment? My belief is that it is both. Not a simple answer.
Anyway, as someone who has studied and read extensively on this topic for decades, I'll share my opinion later.
While I don't dispute your comment regarding black IQ, I also note that all IQs, in general, throughout the world have risen over the decades since that book. In fact, they have risen steadily since IQ was first identified and tracked.