Some simple math here shows that one cannot believe in a purely genetic explanation for the gap between Africans & Americans and the gap between black & white americans. I don't think Watson said he believed in a purely genetic explanation though. I would also note that environment is not always all that malleable, Judith Harris (author of "The Nurture Assumption") discusses "non-shared environment" in "No Two Alike", while genes may become more and more malleable with time. Attempts to raise IQ have not been all that successful, with Head Start gains disappearing after a few years, though efforts to introduce iodine into the diets of third worlders may work as they seem to have in the first world.
The remarkable observation that medical spending has zero net marginal effect is shocking, but not completely unprecedented.
According to Spiegel in "Too Much of a Good Thing: Choking on Aid Money in Africa", the Washington Center for Global Development calculated that it would require $3,521 of marginal development aid invested, per person, in order to increase per capita yearly income by $3.65 (one penny per day).
The Kenyan economist James Shikwati is even more pessimistic in "For God's Sake, Please Stop the Aid!": The net effect of Western aid to Africa is actively destructive (even when it isn't stolen to prop up corrupt regimes), a chaotic flux of money and goods that destroys local industry.
What does aid to Africa have in common with healthcare spending? Besides, of course, that it's heartbreaking to just say no -