A study of illegitimate children conceived as the result of liaisons between U.S. serviceman and German women during the occupation of Germany after the Second World War found no overall difference in average IQ between whose fathers were black and those whose fathers were white.

Since these children were reared in similar environmental circumstances (i.e., by a German mother under comparable conditions of social status and matched when possible with agreements in the same school classroom), the results provide strong support for environment as the major determinant of racial IQ differences.