The fact that a reasonable hypothesis has not been rigorously proved does not mean that it should be summarily dismissed. It only means that we need … - Arthur R. Jensen

I had begun by trying, for the sake of scholarly thoroughness, merely to write a short chapter for my book on the ‘culturally disadvantaged’ that I expected would succinctly review the so-called nature-nurture issue only to easily dismiss it as being of little or no importance for the subsequent study of the causes of scholastic failure and success. I delved into practically all the available literature on the genetics of intelligence, beginning with the works of the most prominent investigator in this field, Sir Cyril Burt, whom I had previously heard give a brilliant lecture entitled The Inheritance of Mental Ability’ at University College, London in 1957. The more I read in this field, the less convinced I became of the prevailing belief in the all-importance of environment and learning as the mechanisms of individual and group differences in general ability and scholastic aptitude. I felt even somewhat resentful of my prior education, that I could have gone as far as I had—already a fairly well-recognized professor of educational psychology—and yet could have remained so unaware of the crucial importance of genetic factors for the study of individual differences.

[Interview: Responding to a question about whether it was smart to publish his 1969 article at the time he did] In retrospect, however, I would hope that I would not have changed a thing in that article, even if I had been able to imagine the supposed "storm" it caused. I will be ashamed the day I feel I should knuckle under to social-political pressures about issues and research I think are important for the advance of scientific knowledge.

The study of inbreeding depression seems to me especially important in the study of human abilities, because inbreeding depression indicates genetic dominance, and the presence and degree of dominance are related to natural selection for the trait in the course of its biological evolution. It was of great interest to me to discover, for example, that of the several ability factors that can be extracted from the various subtests of the Wechsler Intelligence Scale for Children, the one that shows the greatest susceptibility to inbreeding depression is the g factor (Jensen, 1983b). This finding indicates that one of our most widely used standard psychometric tests of intelligence yields scores that reflect some part of the variance in the biological intelligence that has developed in the course of human evolution.