Theories Of Intelligence Essay

Ideas about the nature of human intelligence have long historical roots. However, it was not until the late nineteenth century that modern theories of intelligence emerged among European and American researchers. These theories, which stressed the importance of scientific measurement, also marked the rise of experimental psychology as an academic discipline. The ways in which experimental psychologists conceptualized and measured intelligence would have a profound impact on American society, especially in relation to how American public schools structured learning opportunities for students in the first half of the twentieth century. This entry looks at the evolution of theories about intelligence during the nineteenth and twentieth centuries.

Early Influences

During much of the nineteenth century, theories of intelligence focused on measuring the size of human skulls. Physical anthropologists such as Samuel Morton and Paul Broca attempted to correlate cranial size and capacity with intellectual potential. This line of inquiry was marked by faulty methods of data collection and errors in experimental design. It also was infused with an ideology that purported the existence of innate intellectual differences between “superior and inferior races,” reflecting the dominant White European and American cultural bias at the time.

By the second half of the nineteenth century, Charles Darwin’s theory of evolution also began to influence how European and American social scientists thought about intelligence. Darwin’s notion that some species were destined to die off and others adapt and survive was appropriated by many social scientists, arguing that cultures, races, and classes of people probably adhered to the same evolutionary dynamic. Like their earlier nineteenth-century counterparts, these Social Darwinists believed that superior intellectual abilities were associated with Western European culture and the upper classes. At the beginning of the twentieth century, this preoccupation with individual and group differences in intelligence would form the conceptual foundation for the first modern theories of intelligence.

Modern theories of intelligence emerged with the rise of experimental psychology as an academic discipline. Psychology had been seen as a branch of philosophy in the nineteenth century, but this shifted as major advances occurred in the medical sciences. Beginning in the 1870s, laboratory experiments in biology produced dramatic breakthroughs in the diagnosis, cure, and prevention of contagious diseases. These methods were soon applied to investigations of the human mind by researchers in the “new psychology” who sought a more empirical approach to the study of intelligence.

As early as the 1870s, the first experimental psychologists in Germany began clinical experiments that studied the relationship between the mind and body. Wilhelm Wundt established the first laboratory dedicated to uncovering the structure of the mind. Wundt and other German researchers believed that intellectual thought was rooted in the nervous system and that by measuring reaction times to physical sensations, they could discover underlying mental functions.

Wundt’s work attracted attention among both European and American researchers. Most prominent among the European researchers was English statistician Francis Galton. Galton was greatly influenced by Darwin’s theory of evolution, inspiring him to found the eugenics movement. Eugenics claimed that some individuals and “racial” groups were hereditarily predisposed to low intelligence, crime, and poverty. Galton believed that scientific experiments in the 1880s attempted to prove that there were fundamental intellectual differences between classes and races of people. Instead of measuring skull sizes, Galton thought that experiments in reaction time would reveal these differences. Although Galton’s experiments never yielded the results he expected, American psychologists were impressed with his research and wanted to bring the scientific rigor of European experimental methods to the United States.

One of the first American psychologists to adapt the work of Wundt and Galton was James Cattell. He had studied under Wundt and was influenced by Galton’s eugenics ideas. Like Wundt, his experiments focused on stimulus/response protocols, but Cattell also added his own tests of memory and judgment. In 1890, Cattell published what is considered the first “mental test.” Unlike Wundt, Cattell was less interested in using experiments to uncover the general structure of the mind but was more concerned in measuring individual and group differences in people’s reactions to a variety of tests, believing that a person’s heredity would have a greater influence on a particular test score than one’s environmental background. Cattell could never ascertain the relative influence that heredity and environment had on how people responded to his test items, but his experiments foreshadowed debates later in the twentieth century about the nature of intelligence.

Alfred Binet And Intelligence Tests

Although American interest in the nature of intelligence gained momentum in the first decade of the twentieth century, it would be the experiments of French psychologist Alfred Binet that laid the foundation for the measurement of intelligence in the twentieth century. Ironically, Binet approached his work with little theoretical conception of how the mind worked, yet he created a test that would be the means for actualizing the dominant theories of intelligence among American researchers in the first decades of the twentieth century. Unlike previous experimental psychologists who were interested in reaction times, Binet sought to measure the higher, complex functions of the mind that people might encounter in real-life situations.

His experiments with French schoolchildren in the early 1900s aimed to discover intellectual differences between “normal” achieving students and those who were “subnormal.” Binet and his colleague, Theodore Simon, devised a series of tasks of ascending difficulty that could be done in a relatively short time. He discovered that, on average, the older the students were, the better they did. Those above the average were considered to have a “mental age” beyond their chronological age, and those below the average were considered to have one that was lower. At the time, this was a major contribution to how intelligence was thought of and measured by psychologists in Europe and the United States.

Binet himself was unsure of what intelligence ultimately was but remained convinced that it was, to a certain degree, pliable and subject to change depending upon the educational interventions employed by teachers. American psychologists were quick to adapt his new intelligence test to an American setting while ignoring Binet’s cautions that intelligence was probably not a fixed and unchangeable cognitive function.

The U.S. Approach

Henry Goddard was the first American psychologist to bring Binet’s test to the United States. Goddard and other prominent psychologists in the 1910s, such as Lewis Terman and Robert Yerkes, believed that the test measured a fixed intellectual quantity that was relatively unchanged over a person’s lifetime. Where Binet was tentative about the nature of intelligence, the American creators of intelligence tests believed that intelligence was principally determined by heredity and was a fixed entity that could be objectively measured and ranked in a standardized manner.

This new approach to intelligence by American experimental psychologists occurred within a historical context of dramatic social change. Large-scale immigration from southern and eastern Europe and internal migrations from rural areas swelled the populations of American cities. Concomitantly, the growth of American industry resulted in the need for an expanding and increasingly differentiated workforce. Schools were caught up in the changes occurring in the cities and industry. Urban school officials in particular were looking for new ways to educate a growing and diverse student body.

It is within this social milieu that modern theories of intelligence and the intelligence test emerged. Both theory and the test came together with the testing of 1.7 million Army recruits in 1917. The publicity given to the tests and the ranking of scores into such categories as “moron,” “normal,” and “genius” generated intense fears and hopes among the public. Many interpretations of the test scores suggested that intelligence was unevenly distributed among different ethnic groups. Nativists argued that something needed to be done to stop the influx of “inferior immigrant stock.” At the same time, school administrators hoped that the new IQ test could be a scientific instrument capable of efficiently ranking and sorting their growing school population into appropriate learning tracks.

After World War I, the new IQ test became the sine qua non for measuring intelligence. The conception of intelligence as fixed, hereditarily determined, relatively unchangeable, and measurable through timed individual and group tests became the dominant theory within the experimental psychological community. In turn, both the theory and test were embraced by large numbers of school districts across the United States. By 1924, nearly 70 percent of American urban school districts were using IQ tests to assist in the placement of students into ability-based learning groups. By 1930, more than 130 standardized IQ and achievement tests were being used by American schools to classify their student population.

Dissents to the dominant theory of a fixed and hereditarily determined theory of intelligence emerged within the research community in the 1920s and increased throughout the 1930s. By the mid-1930s, there was no longer a consensus among researchers that intelligence was hereditarily determined. Since that time, there have been recurring debates about the relative influence of environment and heredity upon a person’s intellectual potential. And even though racial theories of intelligence have largely been discredited, the notion that an externally timed and standardized test can provide an accurate and objective measure of one’s intelligence has endured to this day.


  1. Cianciolo, A. T., & Sternberg, R. J. (2004). Intelligence: A brief history. Malden, MA: Blackwell.
  2. Cravens, H. (1988). The triumph of evolution: American scientists and the heredity-environment controversy (2nd ed.). Baltimore, MD: Johns Hopkins University Press.
  3. Gould, S. J. (1996). The mismeasure of man (2nd ed.). New York: W. W. Norton.
  4. Sokal, M. (1990). Psychological testing and American society: 1890–1930. New Brunswick, NJ: Rutgers University Press.
  5. Zimmerman, B. J., & Schunk, D. H. (Eds.). (2003). Educational psychology: A century of contributions. Mahwah, NJ: Lawrence Erlbaum.

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