Chapter 5 – The Hereditarian Theory of IQ

An American Invention

Alfred Binet and the Original Purposes of the Binet Scale

Alfred Binet, a Parisian psychology professor, began his study of intelligence with craniometry. However, after publishing several studies measuring the skulls of young students, he grew skeptical Paul Broca’s popular method. More times than not, Binet found no significant differences in skull size of the students, and sometimes, the differences he did find contradicted Broca’s belief that more intelligent people had bigger skulls. Eventually, Binet realized his preexisting beliefs about intelligence were unconsciously affecting the accuracy of his measurements

After coming to this realization, Binet nearly gave up his studies of intelligence. However, tasked by the French government to create an exam that detected school children in need of extra help, he later returned with a new approach to the problem of intelligence. Rather than test knowledge the students may have learned in school, the exam tested reasoning skills with a series of tasks. The students were then given a single number to rate their intelligence, based on the most complicated task the students could perform at their age. Known as their “mental age,” this number was then divided by the student’s actual age to produce the “intelligence quotient,” or “IQ” as it is still known today. 

Though Binet worked hard to develop such a test, it was clear he believed intelligence was a phenomenon far too complex for any test to accurately measure. As such, he became afraid the test would be misused by teachers, and children might be labeled as unintelligent. Later, when Binet’s IQ test was brought to the United States, his worst fears came true. 

Gould views the American misuse of IQ tests as being based on two fundamental errors: reification and hereditarianism. According to Gould, American psychologists reified Binet’s IQ scoring system and assumed it had the capability to measure something as complex as intelligence. With hereditarianism, the view that an individual’s mental and physical traits are largely inherited and not susceptible to change after birth, Gould believed American psychologists equated inheritance with inevitability. Though Gould does not dispute mental ability is, to a certain extent, inherited, he recognizes just because a mental ability is inherited does not make that ability inevitable. 


H.H. Goddard and the Menace of the Feeble-Minded

One person who embraced Binet’s IQ tests was H.H. Goddard, director of the Vineland Training School for Feeble-Minded Girls and Boys in New Jersey and, more notably, the man who coined the term “moron.” In embracing Binet’s IQ tests, Goddard did so with both reification and hereditarian errors: he believed the IQ score did capture the sum total of an individual’s intellectual ability, and intelligence is almost 100% inheritable and unalterable. 

Based on his beliefs about intelligence, Goddard became a leading figure in the eugenics movement. He advocated no morons should be allowed to marry or reproduce and no morons should be allowed to enter the country via immigration. 


Lewis M. Terman and the Mass-Marketing of Innate IQ

Another person who embraced, but modified, Binet’s IQ tests was Stanford University psychology professor Lewis M. Terman. According to Gould, Terman’s modification decreased the reliability of the IQ test by marking creative answers to questions as wrong, thus falsely lowering the IQ score. Terman also modified the test by creating a written version that could be administered to hundreds of students and introducing a new point scale scoring system. This new modified IQ test became known as the Stanford-Binet test. 

Terman’s motivation in modifying Binet’s IQ test was to mass administer the test to students and segregate the morons from the non-morons. According to Terman, this would be a major benefit to society, as morons would be surveilled and protected by the system. Terman also wanted to use scores from the new Stanford-Binet test as a means of helping workers decipher the most appropriate occupation for them. Finally, Terman predicted IQ testing of nonwhite groups would reveal significant differences between the various races in general intelligence.


R.M. Yerkes and the Army Mental Tests: IQ Comes of Age

The final person who embraced Binet’s IQ tests was Harvard University psychologist professor Robert M. Yerkes. With World War I looming, Yerkes administered IQ tests to 1.75 million army recruits, ushering in the era of mass intelligence testing in the United States.

From the data, Yerkes drew two main conclusions: the average mental age of white male adults was only 13, just above that of morons, and black people lie at the bottom of the IQ scale.

Though several non-hereditarian explanations of these results existed, Yerkes and his colleagues rejected all of these explanations and insisted their results proved the heritability of intelligence. 

The results from these tests were further used to support eugenicist and racial movements for years afterwards; the inferiority of nonwhites and immigrants was no longer a theory, but a proven fact. Society could no longer ignore the burden of these groups on national progress. Thus Yerkes and C.C. Brigham, a Princeton psychology professor, proposed restrictions on immigration and reproduction to prevent “defective strains” in the American population.