THE SATURDAY EVENING POST The Her it ability of Intelligence of l.Q.'s going from 90 to 110. l.Q. children in later adulthood markedly excelled ARTHUR R. JENSEN Significance of the LQ. the general population on every indicator of Can the LQ. tell us anything of practical im- achievement that was examined: a higher level of The question of why people differ in intelli- portance? Is it related to our commonsense education completed; more scholastic honors and gence bas been asked for centuries, but a scientifi- notions about mental ability as we ordinarily think awards; higher occupational status; higher income; cally acceptable answer did not become wholly of it in connection with educational and occupa- production of more articles, books, patents, and possible until psychologists devised techniques for tional performance? Yes, indeed, and there is no other signs of creativity; more entries in Who's measuring intelligence quantitatively and objec- doubt about it. The massive evidence from psy- Who: ii lower mortality rate; better physical and tively. The first really useful intelligence test was chological, educational and industrial research, mental health; and a lower divorce rate. Also, they devised in 1905 by the French psychologist Alfred and research in the armed forces, is unequivocal. have much brighter children than the average; their Binet. Binet's early test was later revised and im- We know, for example, that no other single fact average LQ. is 133, a level which is exceeded by proved by Lewis Terman at Stanford University; that we are now able to ascertain about a child only 2 percent of all the children in the general the now-famous test that resulted from these ef- gives us a better prediction ofhis future scholasfic population. forts is known as the Stanford-Binet Intelligence performance than his LQ. obtained after age 5 or Findings such as these establish beyond a doubt Scale. It is stiU the most widely used test of general 6. (Below this age LQ. tests become less accurate that LQ. tests measure characteristics that are intelligence. indicators of the child's later mental development, obviously of considerable importance in our pres- There are other intelligence tests, and although and below 2 or 3 years of age test scores have prac- ent technological society. To say that the kind of many of them appear to be quite different from tically no predictive value.) ability measured by intelligence tests is irrelevant one another, all actually measure much the same The LQ. obtained after 9 or 10 years of age also or unimportant would be tantamount to repudi- general ability. That is to say, if we administer predicts final adult occupational status to almost ating civilization as we know it. several seemingly quite different intelligence tests as high a degree as it predicts scholastic per- The Causes of LQ. Differences to a large number of persons, their scores on all the formance. When various occupations are ranked The layman usually asks: "Is intelligence due to tests will be in pretty much the same rank order. for average income and for the general public's heredity or environment?" The scientist promptly Those who score high on one test will tend to score average judgment of the occupation's prestige and answers: "Both." WitlKJut heredity and environ- high on the others, and those who score low on one desirability, this rank order is found to be highly ment there simply is no intelligence. Obviously test will usually score low on all the others. This related to the average LQ. level of the persons in every person must have had a biological inheri- fact of correlation among all tests of intelligence these occupations. There is of course a wide spread tance of genes from his parents and must have led Charles Spearman, the famous English psy- of l.Q.'s in nearly every occupation, but the aver- grown in an environment, or he wouldn't even be chologist, to conclude that there is a general fac- age LQ. of persons within a particular occupation here to take an LQ. test. So, of course, both hered- tor, "g," which is common to all tests of intelli- is closely related to that occupation's standing in gence. We know that it is practically impossible to ity and environment are essential for the exis- terms of its average income and the amount of tence of the individual or any of his physical and make up a mental test having any degree of com- prestige accorded to it by the general public. plexity which does not involve "g." We can per- mental characteristics. One of the most convincing demonstrations haps most clearly characterize "g" as an ability for But when scientists actually study this prob- that LQ. is related to "real life" indicators of abil- abstract reasoning and problem solving, for seeing lem, we find that they do not even ask the lay- ity was provided in a classic study by Terman and relationships, and for grasping concepts. man's question. The question to which scientists his associates at Stanford University. In the 192O's have sought an answer can be stated as follows: A person's score on an intelligence test is usu- they selected a total of 1,528 children with Stan- How much of the variation among persons in a ally expressed as an LQ. (for Intelligence Quo- ford-Binet l.Q.'s above 140. The average LQ. of given population is attributable to differences in tient). The test is standardized in the general popu- the group was 152. These children were investi- their environments and how much to differences lation in such a way that the average LQ. at any age gated periodically over the years up into their in their genetic endowments? adulthood. (Most of them are now in their fifties.) is set at IOO, and the middle 50 percent of the Numerous studies conducted by psychologists Terman found that for the most part these high- population falls within the so-called average range and geneticists over the last 40 or 50 years provide Arthur R. Jensen is Professor of Educational Psychology and Research Psychologist at the Institute of Human Learning at the Univer- sity of California (Berkeley). Since 1958 his research has included individual differences in human learning, and cultural, develop- mental, and genetic determinants of intel- ligence in learning ability. He has published over 100 articles and chapters in psychological and educational Journals and books. His re- searches have suggested a strong genetic fac- tor in human intelligence. His article in the Harvard Educational Review (Winter 1969) has caused considerable controversy. 13 THE SATURDAY EVENING POST Summer 1972 an answer to this question. The answer is un- Do I.Q. Tests Measure that there are other important human qualities be- ambiguous and is generally agreed upon by all Intelligence? sides the ability to take scholastic aptitude tests, scientists who have considered all the evidence. but as Wing and Wallach (1971) have shown, This evidence strongly supports the conclusion DAVID c. MCCLELLAND admissions officers may believe they take these that genetic factors are much more important than Psychology has one great practical success to its other qualities into account but in fact their selec- environmental influences in accounting fot indi- credit in the twentieth century-namely the intelli- tion decisions can be almost perfectly predicted by vidual differences in I.Q. How much more impor- gence testing movement. Many tests have been aptitude-test scores alone. The desite to select tant? The evidence indicates that genetic factors devised which predict success in school with re- more "intelligent" people for schooling or for account for at least twice as much of the variation markable regularity. Literally tens of thousands of almost any occupation proves overpowering. It in l.Q.'s as environmental factors. This conclusion validity coefficients have been calculated, demon- quickly reduces other qualifications to insignifi- has one main limitation. Since all of the major strating that those who score higher on aptitude or cance. studies in this field were conducted with samples intelligence tests usually do better in their school of Caucasian European and North American popu- work. Selecting, at random, a finding which is While the intelligence-testing movement in the lations, we cannot confidently generalize their quite typical for the United States, I recently ob- United States has been moving on from one tri- conclusions to other populations, especially those served in a longitudinal study to be reported by umph to the next, some questions have been raised with very dissimilar environments. Costa (1972) that Kuhlman-Anderson I.Q. scores about its theoretical underpinnings, both by obtained in the sixth grade correlated 0.59 with scholars and by policy makers who wonder if its What are the kinds of evidence that lead to the twelfth-grade rank in class. In other words know- growing power over people's lives is justified. One conclusion that genetic differences outweigh ing how a child scores on an intelligence test when difficulty with tests has long been known but little environmental differences in accounting for indi- he is eleven or twelve years old enables you to pre- commented on perhaps hecause its seriousness has vidual differences in I.Q.? Most of this evidence, as dict fairly accurately how well he will be doing in not been fully appreciated. It is very simply that if it is found in the scientific hterature, depends school some six or seven years later. Rank in class academic achievement tests are taken seriously as upon quite technical methods of analysis de- at graduation from secondary school in turn pre- measures of real competence, then the quality of veloped in a specialty known as quantitative genet- dicts whether he can go on to the university and education does not seem to contribute to improv- ics or population genetics.