In a previous post, I argued that the black-white cognitive ability gap is responsible for many of the undesirable social disparities that we find between blacks and whites in the United States – including disparities in income, education, occupation, and crime. This means that the cause of the cognitive ability gap is extremely important, as this informs how (and if) we can reduce these social disparities. In another post, I examined some arguments on whether the gap is due to genetic differences or environmental differences. In that post, I concluded that we must use direct data to quantify the degree to which the black-white cognitive ability gap is due to genetic differences vs environmental differences. In this post, I will attempt to review all such direct data. I conclude that a primarily environmental explanation of the gap is most compatible with all the relevant direct data.