Race differences in IQ: Hans Eysenck’s contribution to the debate in the light of subsequent research

Hans Eysenck was one of the earliest protagonists in the controversy over race and intelligence. He believed that the observed variability in IQ scores is genetically determined to a high degree (80% heritability) and that, in consequence, the Black–White IQ gap in the US is due predominantly to genetic factors. Subsequent investigations have confirmed that IQ is indeed heritable, though at a level substantially below 80%, and a deeper understanding of population genetics has shown that race differences in IQ could be determined entirely by environmental factors even if its heritability were as high as Eysenck believed it to be. Several lines of research, notably racial admixture studies, racial crossing studies involving interracial parenting or adoption, and especially investigations using more recent techniques of molecular genetics, have provided evidence suggesting that the Black–White IQ gap is not determined significantly by genetic factors.