Beginning in the 1900s, scientists began to develop different methods for measuring intelligence. These tests were used often to justify racial and ethnic discrimination. The results of these intelligence tests were influential in shaping U.S. immigration policy that limited immigrants from Southern and Eastern Europe, and in justifying race-based segregation in public education, and U.S. conscription during World War I. Previously, the scientific debate centered largely on perceived differences in racial intelligence based on cranial size.
French psychologist Alfred Binet is credited with creating the the first modern intelligence test, the Binet-Simon intelligence scale, in 1905. Binet's objective in developing the test was to identify students who needed special help in school. However, Binet recognized the limitations of the test in understanding cognition and intellect; he did not intend that the test be used as a measurement of intelligence. Binet and his colleague Theodore Simon published revisions of the intelligence scale in 1908 and 1911. Lewis M. Terman of Stanford University, a prominent eugenist ("eugenics" is the science of improving a human population through selective breeding) and member of the Human Betterment Foundation, published his refinement of the Binet-Simon scale in 1916. Terman incorporated German psychologist William Stern's concept that mental age/chronological age times 100 would quantify intelligence, thus creating the intelligence quotient or IQ. Terman's test, which he renamed the Stanford-Binet Intelligence Scale, formed the basis for one of the modern intelligence tests, although IQ is calculated differently today.
Harvard-educated psychologist, ethologist and primatologist, Robert Mearns Yerkes, known for his work in Army intelligence testing in World War I and in the field of comparative psychology, was an early standout in the field of primate intelligence and chimpanzee and gorilla behavior. The theory of behaviorism was developed by Yerkes and his colleague John B. Watson.
In 1917, Yerkes, as the president of the American Psychological Association, urged the group to initiate several programs during World War I. The Army's Alpha and Beta intelligence tests were his creation, and they were administered to over a million U.S. soldiers during the war. The results of the tests led to the conclusion that recent immigrants from Southern and Eastern Europe had considerably lower scores than earlier immigrants from Northern Europe. Eugenicists relied on these results as ammunition for their campaign for immigration restrictions. The test results, however, were later criticized as having been more a measure of acculturation than of intelligence, since the test scores correlated closely with the number of years spent living in the U.S.
Psychologist Cyril Burt was influenced by the British class system, and decried what he saw as the decline of the "British race." Influenced by Francis Galton's work, Burt was also drawn to the theories of Charles Spearman—and in fact tried to claim Spearman's g-factor theory of intelligence as his own—in an effort to substantiate his theory of the heritability of intelligence with quantitative analysis. Burt was a member of the British Eugenics Society. He was appointed professor and chair of psychology at University College, London, in 1931 taking over Spearman's position. At the university, Burt influenced many students, among them Arthur Jensen and Chris Brand.