I wonder if you read this article yourself, or if you found it and threw it at me.
The idea that the average intelligence of Africans is severely decreased relative to that of people in other parts of the world simply does not accord with the experience of people who have worked on or even visited that continent…
Africanist archaeology itself for a long time shared many of those assumptions, particularly expressed by an unwillingness to accept evidence for indigenous African cultural advance…
African history is entirely comparable to that of other regions and other continents in terms of the human capabilities that it evokes…
This implies African domestication of millet, sorghum and cowpea during the fifth millennium BP. This is certainly later than was the case in many other areas of the world…
The picture provided by African archaeological data is entirely incommensurate with claims by Rushton and his colleagues that African populations suffer severe cognitive deficits or other behavioural disadvantages when compared with human populations from Europe and Asia…
Examination of archaeological data on the culture history of African populations, and comparison of those data with data from other parts of the world, yields no evidence for the behavioural and cognitive disparities claimed by Rushton. African cultural history is entirely comparable with that of other regions of the world.
http://nilevalleypeoples.blogspot.ca/2010/05/blog-post.html
The author maintains that the performance of blacks in Africa in the economy belies the assertion that their average IQ is 70. Most businesses in Africa, even small businesses are operated by people form outside the area. This is also true in the United States. Small shops, grocery stores, and so on are usually owned and operated by immigrants.
The author also maintains that the archaeological record of sub Saharan Africa does not indicate intelligence differences with other races. Agriculture began ten thousand years ago in the Near East. Whites began it. Civilization began five thousand years ago in the Near East. Whites began it. The Bantu may have begun agriculture four thousand years ago, but they never created a civilization in any way equivalent to those in Mesopotamian and Egypt, or even in the New World.
The Bantu did build towns with brick and stone buildings, but they never developed their own systems of writing and mathematics the way the Mayans did in the New World. They adopted iron age technology about two and a half thousand years ago, but they learned if from the Nubians, who learned it from the Egyptians.
Professor Rushton does seem to give too much importance to living in a cold climate. The Neanderthals lived in Europe during several ice ages, but they were less intelligent than the Cro Magnons who displaced them.
The 10,000 Year Explosion, which I reviewed here:
Attributes the superior intelligence of whites and Orientals to many more thousands of years of experience with agriculture than Negroes have, and to several thousand years of urban civilization.