How much of the failure of the African countries is due to their average lower intelligence and how much is that a consequence of other systemic problems (e.g. lack of institutions) that also make the maintenance of modern technologies difficult?

I get the impression that "average lower intelligence" is a big cause of systemic problems, like lack of institutions. I'm reminded of Yvain's example that, in Haiti, they could not understand sorting things numerically or alphabetically. This meant bureaucratic institutions were basically worthless: "where is your file? Let me look at all of the files and try to find yours."

Edit: Also, see this paper.