Culture and environment have a huge impact on IQ. For instance, a thread from yesterday mentioned the Romanian orphans who were discovered after the fall of communism, who were barely functioning. They spent their lives in a crib with little to no human interaction. I have heard from colleagues working with Africans that in general, because of high infant mortality, mothers do not place nearly the value on their infants as we do in the west. A child gains in value only as it ages, as the investment into it has been greater and has a likelier chance of “paying off” as a productive adult family member. I would imagine that an infancy strapped to a mother’s back as she works and generally ignored other than for the most basic maintenance would have an impact on brain development.
That, plus substance abuse during pregnancy...fetal alcohol syndrome.
There’s likely a parallel between ghetto life and conditions on an Indian reservation. Both groups have a tendency to stay put, and suffer.