African IQ and mental retardation

Rushton and Jensen (2005), in an extensive review of racial differences in intelligence test scores, assert that some part of the difference between blacks and whites in mean intelligence (IQ) scores is genetic in origin. They cite earlier reviews by Lynn (1991) and by Lynn and Vanhanen (2002), as well as several more recent studies, which are said to indicate that the mean IQ of sub-Saharan black Africans is about 70 - at the borderline of mental retardation. The present article reviews critically both the original studies and the ways in which the reviewers have described the findings of the studies.