ALMOST a century ago Alfred Binet, a gifted psychologist, was asked by the French Ministry of Education to help determine who would experience difficulty in school. Given the influx of provincials to the capital, along with immigrants of uncertain stock, Parisian officials believed they needed to know who might not advance smoothly through the system. Proceeding in an empirical manner, Binet posed many questions to youngsters of different ages. He ascertained which questions when answered correctly predicted success in school, and which questions when answered incorrectly foretold school difficulties. The items that discriminated most clearly between the two groups became, in effect, the first test of intelligence.
Binet is a hero to many psychologists. He was a keen observer, a careful scholar, an inventive technologist. Perhaps even more important for his followers, he devised the instrument that is often considered psychology's greatest success story. Millions of people who have never heard Binet's name have had aspects of their fate influenced by instrumentation that the French psychologist inspired. And thousands of psychometricians -- specialists in the measurement of psychological variables -- earn their living courtesy of Binet's invention.
Although it has prevailed over the long run, the psychologists' version of intelligence is now facing its biggest threat. Many scholars and observers -- and even some iconoclastic psychologists -- feel that intelligence is too important to be left to the psychometricians. Experts are extending the breadth of the concept -- proposing many intelligences, including emotional intelligence and moral intelligence. They are experimenting with new methods of ascertaining intelligence, including some that avoid tests altogether in favor of direct measures of brain activity. They are forcing citizens everywhere to confront a number of questions: What is intelligence? How ought it to be assessed? And how do our notions of intelligence fit with what we value about human beings? In short, experts are competing for the "ownership" of intelligence in the next century.
THE outline of the psychometricians' success story is well known. Binet's colleagues in England and Germany contributed to the conceptualization and instrumentation of intelligence testing -- which soon became known as IQ tests. (An IQ, or intelligence quotient, designates the ratio between mental age and chronological age. Clearly we'd prefer that a child in our care have an IQ of 120, being smarter than average for his or her years, than an IQ of 80, being older than average for his or her intelligence). Like other Parisian fashions of the period, the intelligence test migrated easily to the United States. First used to determine who was "feeble-minded," it was soon used to assess "normal" children, to identify the "gifted," and to determine who was fit to serve in the Army. By the 1920s the intelligence test had become a fixture in educational practice in the United States and much of Western Europe.
Early intelligence tests were not without their critics. Many enduring concerns were first raised by the influential journalist Walter Lippmann, in a series of published debates with Lewis Terman, of Stanford University, the father of IQ testing in America. Lippmann pointed out the superficiality of the questions, their possible cultural biases, and the risks of trying to determine a person's intellectual potential with a brief oral or paper-and-pencil measure.
Perhaps surprisingly, the conceptualization of intelligence did not advance much in the decades following Binet's and Terman's pioneering contributions. Intelligence tests came to be seen, rightly or wrongly, as primarily a tool for selecting people to fill academic or vocational niches. In one of the most famous -- if irritating -- remarks about intelligence testing, the influential Harvard psychologist E. G. Boring declared, "Intelligence is what the tests test." So long as these tests did what they were supposed to do (that is, give some indication of school success), it did not seem necessary or prudent to probe too deeply into their meaning or to explore alternative views of the human intellect.
Psychologists who study intelligence have argued chiefly about three questions. The first: Is intelligence singular, or does it consist of various more or less independent intellectual faculties? The purists -- ranging from the turn-of-the-century English psychologist Charles Spearman to his latter-day disciples Richard J. Herrnstein and Charles Murray (of The Bell Curve fame) -- defend the notion of a single overarching "g," or general intelligence. The pluralists -- ranging from L. L. Thurstone, of the University of Chicago, who posited seven vectors of the mind, to J. P. Guilford, of the University of Southern California, who discerned 150 factors of the intellect -- construe intelligence as composed of some or even many dissociable components. In his much cited The Mismeasure of Man (1981) the paleontologist Stephen Jay Gould argued that the conflicting conclusions reached on this issue reflect alternative assumptions about statistical procedures rather than the way the mind is. Still, psychologists continue the debate, with a majority sympathetic to the general-intelligence perspective.
The public is more interested in the second question: Is intelligence (or are intelligences) largely inherited? This is by and large a Western question. In the Confucian societies of East Asia individual differences in endowment are assumed to be modest, and differences in achievement are thought to be due largely to effort. In the West, however, many students of the subject sympathize with the view -- defended within psychology by Lewis Terman, among others -- that intelligence is inborn and one can do little to alter one's intellectual birthright.
Studies of identical twins reared apart provide surprisingly strong support for the "heritability" of psychometric intelligence. That is, if one wants to predict someone's score on an intelligence test, the scores of the biological parents (even if the child has not had appreciable contact with them) are more likely to prove relevant than the scores of the adoptive parents. By the same token, the IQs of identical twins are more similar than the IQs of fraternal twins. And, contrary to common sense (and political correctness), the IQs of biologically related people grow closer in the later years of life. Still, because of the intricacies of behavioral genetics and the difficulties of conducting valid experiments with human child-rearing, a few defend the proposition that intelligence is largely environmental rather than heritable, and some believe that we cannot answer the question at all.
Most scholars agree that even if psychometric intelligence is largely inherited, it is not possible to pinpoint the sources of differences in average IQ between groups, such as the fifteen-point difference typically observed between African-American and white populations. That is because in our society the contemporary -- let alone the historical -- experiences of these two groups cannot be equated. One could ferret out the differences (if any) between black and white populations only in a society that was truly color-blind.
One other question has intrigued laypeople and psychologists: Are intelligence tests biased? Cultural assumptions are evident in early intelligence tests. Some class biases are obvious -- who except the wealthy could readily answer a question about polo? Others are more subtle. Suppose the question is what one should do with money found on the street. Although ordinarily one might turn it over to the police, what if one had a hungry child? Or what if the police force were known to be hostile to members of one's ethnic group? Only the canonical response to such a question would be scored as correct.