This paper, focusing on differences between Caucasians and Negroes in the United States, summarizes from a "scientific standpoint" the main facts and theoretical issues involved in the study of human racial differences and behaviors. Three principles are considered to govern the orientation of this document: (1) objective research and knowledge are possible and should not be entangled with political and social policy; (2) phenomena are better explained by theory as opposed to ad hoc explanations; and (3) conclusions expressed in terms of statistics and probabilities must be accepted, with their tentative nature kept in mind. Among the topics dealt with are: (1) mutation and drift, migration, and selection processes affecting evolutionary differentiation; (2) formulation of heritability of group differences; (3) psychometric evidence for the author's conclusions; and (4) hypotheses of culture-biased tests and environmental foci. It is reiterated that it is highly probable that genetic as opposed to environmental factors are involved to a substantial degree in the lower average IQ of American Negro groups. (Author/AM)