The establishment and proliferation of mental testing seems scientifically and culturally at odds with the development of a functionalist perspective in general and behaviorism in particular. While mental testing is founded on the assumptions of relatively fixed mental abilities that differ in degree and kind among individuals, the functionalist proviso, with its focus on performance or adaptive action, eschews individual differences and abstract mental abilities. In some senses, these two programs do champion distinct models of human psychology, one highlighting the organism in its environment and the other fixing on the native content of the organism. However, in their modern form, these models shared intellectual origins in Darwinian Theory: functionalism represented the evolutionary theses of adaptation and selection, and individual differences assessment reflected the evolutionary notion of natural variation.
Interest in classifying and measuring individual differences has not always been linked with evolutionary theory. Nineteenth-century phrenologists and anatomists attempted to measure physical differences, assuming them to be correlates of psychological differences. In the same century, physicians concerned with mental competence devised tests to classify degrees and types of intelligence. However, it was the work of Darwin’s cousin Francis Galton (1822-1911) that set the stage for modern studies of individual differences in psychological abilities. Following Darwinian Theory, Galton’s interest was in measuring various human physical and psychological faculties and demonstrating the heritability of these traits. His design of measuring instruments and statistical methods influenced American psychologists in their efforts to assess individual differences. Inspired by Galton, for instance, James McKeen Cattell developed what he called mental tests and employed them in several studies.
Meanwhile, in France Alfred Binet (1857-1911) and Theodore Simon’s (1873-1961) work on individual differences resulted in the construction of a test of intelligence. Their test was designed in response to the French government’s request for a means to assess schoolchildren whose mental ability was below average. The resultant 1908 Binet-Simon test was therefore practical (not linked to evolutionary theory) and involved calculation of a mental age that took chronological age into account. The scale assumed that mental age increases with chronological age and that these are norms or averages for intelligence at each chronological age.
Binet and Simon’s work quickly made its way to the United States, and its early revisions by two American psychologists illustrate the discipline’s (and culture’s) multiple interests in measuring individual differences. The various projects for quantifying the mind and distinguishing differences between minds, especially in regard to what was believed to be intelligence, clearly if unfortunately demonstrates just how psychology was infused with cultural interests. Henry H. Goddard (1866-1957) studied with Hall at Clark University and undertook research in education and mental deficiency. He employed the early version of the Binet scale to assess and classify grades of the mentally deficient (using classificatory terms such as idiot, imbecile, and moron). Influenced also by evolutionary ideas about the inheritance of individual attributes, Goddard made provocative claims (including his 1913 book The Kallikak Family) about the tendency for feeblemindedness to run in families. A cultural preoccupation with genetic fitness fueled theory and observation alike. Another student of Hall, Lewis M. Terman (1877-1956), found the Binet-Simon test invaluable to his scientific attempts to measure degrees of intelligence. His revisions of their test resulted in a highly successful scale for measuring intelligence and enabled him to further his studies of exceptional or “gifted” children. Terman soon was involved in the preparation of tests for army recruits during World War I. These new tests, Army Alpha for men who could read English and Army Beta for those who could not, introduced a significant alteration in mental testing techniques. As a paper-and-pencil measure it was the first successful use of group testing that provided substantial time savings over individual testing.
In the United States, tests of individual differences met with acceptance and proliferated largely for practical purposes. Intelligence tests were used in education, and other mental tests, devised to assess specific abilities or skills, were developed to aid in personnel selection and vocational training. Yet, in addition to this practical impetus, mental testing served racist purposes; some psychologists wanted to develop theories of individual differences that were in accord with the Darwinian notion of the inheritance of characteristics. Numerous psychologists, for instance, utilized the newly devised intelligence tests and test data to examine supposed racial and ethnic differences in intelligence. Once again, these projects to quantify mental traits were undergirded by dominant cultural beliefs: in many cases, these were racist and sexist. Carl C. Bingham thus analyzed the army test data and concluded that intelligence varied according to nationality. Many psychologists used the tests to ascertain differences in intelligence between Whites and African Americans, most of them concluding that the latter were the inferior group. Yet another use of testing involved development of tests of personality or internal psychic states that could differentiate groups of individuals. For example, in 1936, Terman and Catherine Cox Miles created a test of masculinity and femininity that measured differences between normal men and women, which the intelligence tests purportedly failed to do. Such developments in tests and test usage indicate that the measurement of differences was intimately connected with theories of inheritance (and nature-nurture debates) as well as with the political dynamics of American culture.
Maturing side by side, behaviorism and mental testing both reflected and fostered a major debate about humankind that was to continue for the entire century. The data and theories from these scientific projects provided the framework for debating whether the central psychological characteristics of humans were determined by their biology (nature) or their experiences in the world (nurture). These research programs produced a discourse on nature versus nurture: was intelligence inherited, was educational success the result of learning, do early childhood experiences influence the formation of personality? At no point were these debates simply or only academic. Psychologists’ involvement in eugenics campaigns and their lobbying for immigration laws, for instance, were linked with their deterministic belief in the biological basis of psychological attributes. Likewise, researchers’ arguments for improving the social and educational environment of Negro youth and their appeals for child guidance clinics were guided by belief in the environmental determinants of behavior. The high stakes in nature-nurture controversy were set by such political as well as scientific implications, and the intractability of the debate was established by its historical origins in modern science’s metaphysical distinction between culture and nature.