See the book “the bell curve”.
I think he was alluding to that book when he posted those bell curves. Another conclusion of the book is that unfortunately, the blacks on the low end of the IQ spectrum reproduce at far greater frequency than the Clarence Thomases, Thomas Sowells, Ben Carsons, et al. Instead, low IQ mates with low IQ and gives birth to low (or lower) IQ.
I read it long ago.
It pretty much explains everything you see regarding races and their differences with respect to success in life. It’s not the only factor but definitely a dominant one.
It’s a tragic reality, but a reality nonetheless. Denying it is what has brought us to the dysfunctional society we’re in today.
The best, but not easy, answer is separation, otherwise the dysfunction we see today will only accelerate.