Murray clearly overstates the immutability of human intelligence when he tacitly premises that the architecture and neural functioning of the brain are static. A case in point is the enhancement of neuroplasticity by Adderall (already being prescribed off-label for that specific purpose, eg for professional musicians).
He is also spouting BS in claiming that he is g-constrained from understanding a proof in a mathematical journal.
He accepts that low intelligence leads to emotional deficit and so to social and economic problems, but lacks the wisdom if not the wit to acknowledge causation in the other direction (neurons cannot be recruited to higher centers if they are in high demand below for coping mechanisms because of ubiquitous stressors, eg racial demonization of white children by grade school curricular materials, worrying about getting killed on the way to an inner city school, etc.).
If society needs more g in aggregate, and public schools are first and foremost stress factories, then the indicated course is an end to public education.