I believe culture affects IQ.
I don't know why anyone would even argue it doesn't.
The acrimony always comes up when folks debate what comprises and forms particular culture.
I think geographic isolation has always been a big factor.
Anyhow....you've pushed the big button here and many new age Conservatives prefer to ignore that area of realism.
I've spent a lot of time in Africa too....a whole lot in Sierra Leone in the 80s.
I do not believe one can bring entire cultures through massive change from near bronze age to our era in an historical overnight. Of course, it can be done with individuals and it helps if good leaders are found....something Lower Africa has never had.
Culture is the prime determining factor of success. Here I define "culture" according to the group's attitudes on what is considered admirable and what is contemptable.
A group that confers high status to scholars (as Asian and Jewish culture does) will turn out lots of excellent scholars, as parents will be very focused on the kids learning starting at birth. A culture that reserves its highest status for athletes, musicians, and gangsters will produce lots of those instead
That said, there is an identifiable genetic component, as seen by studies comparing kids adopted and raised by parents of a different racial group to kids raised by parents of their own group