Blacks in predominantly black countries therefore score nearly two full standard deviations below whites and one standard deviation below American blacks. Why do American blacks score higher than sub-Saharan Africans and Afro-Caribbeans? It is primarily because American blacks have an average admixture of 20-25 percent white genes.135 Their IQs have been enhanced by this admixture so that they occupy an intermediate position between whites and those blacks without any white ancestry. But social environment is important also, as the environments of American blacks are considerably better than
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