One salient difference: 90% of the black children of Harlem in 1910 and 1920 --- as recorded by the census --- lived in a household headed by a married mother and father.
Way higher than the figure for white children today. According to the Census Bureaus 2016 "America's Families and Living Arrangements" report, the number of U.S. children under the age of 18 living with 2 parents, father/mother, is now 78% for whites, 85% for Asians.
And blacks? Just 38% are living with two parents, including 22% who are living with two parents who are both in their first marriage.
Nobody is doing as well as the Harlem Renaissance cohort.
Something to think about.
“Something to think about.”
It called the dumbing down of America. The dumb among us set the standards. So, back to your point that IQ means something but it isn’t everything. Ya gotta use it for it to count.