Genetics of Intelligence
At the end of the 1960s, before Arthur Jensen’s Harvard Educational Review monograph appeared, most contemporary behavioral genetic research was conducted with non-human animals, primarily for the purpose of demonstrating that genetic differences among individuals in a population are related to observed behavioral variability. Although Erlenmeyer-Kimling and Jarvik’s (1963) Science review of familial correlations for IQ was reprinted in some psychology and education textbooks and Heston’s (1966) adoption study of schizophrenia had made an impact in the area of psychopathology, the Zeitgeist did not accept the idea that genetic influence on IQ scores is substantial. The data, mostly from the 1920s and 1930s, were largely ignored. Jensen’s (1969a) article made it no longer possible to avoid the issue. He clearly and carefully described quantitative genetic theory with a minimum of jargon, reviewed the data, and concluded that individual differences in IQ scores are substantially due to genetic differences. The section of the mongraph entitled ‘The Inheritance of Intelligence’ (pp. 2859) is still the best introduction to the genetics of intelligence. What is most impressive to me is that this monograph was written only one year after his first article on behavioral genetics appeared (Jensen, 1967).