Robert Yerkes Was Influential in Comparative Psychology

Robert Yerkes in his office at Harvard
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Robert Yerkes (May 26, 1876 - February 3, 1956) was an American psychologist best remembered for his work in the areas of intelligence testing and comparative psychology. He is also known for describing the Yerkes-Dodson law with his colleague John Dillingham Dodson. The Yerkes-Dodson law suggests that there is a relationship between arousal levels and performance.

During Yerkes' tenure as President of the APA, he became involved in developing the Army's Alpha and Beta Intelligence Tests as part of the World War I effort. The tests were extensively used during this time and were taken by millions of U.S. soldiers.

While Yerkes believed that the tests measured native intelligence, later findings revealed that education, training, and acculturation played an important role in performance. Yerkes also became a prominent figure in the eugenics movement, which advocated for harsh immigration restrictions in order to combat what he referred to as "race deterioration."

Best Known For

Early Life

Robert Yerkes grew up on a farm in Breadysville, Pennsylvania. He attended Ursinus College originally intending to become a medical doctor. After graduating in 1897, Harvard University offered him a spot doing graduate work in biology. During his studies at Harvard, he took an interest in animal behavior and began studying comparative psychology. In 1902, Yerkes earned his Ph.D. in psychology.

After graduating, Yerkes took a number of positions to pay the debts he had acquired while completing his education. He started as an instructor at Harvard, later getting promoted to assistant professor of comparative psychology, and taught courses in general psychology during the summer at Radcliffe College. He also took a part-time job as the director of psychological research at the Boston Psychopathic Hospital in Boston, Massachusetts.


In 1917, he was elected President of the American Psychological Association. After the U.S. entered World War I, Yerkes urged the APA to get involved in contributing psychological expertise to the war effort. A number of committees were formed, including one designed to measure intelligence in order to identify Army recruits who were particularly suited for special positions.

The work of the committee, which included psychologists such as Lewis Terman, Henry Goddard, and Carl Brigham, led to the development of the Army Alpha and Army Beta tests. The tests had been administered to approximately two million men by the time the war was over.

The tests are important in psychology history because they were the first group intelligence tests and helped popularize the concept of intelligence testing. The results of the tests were also used by eugenicists to advocate for harsher immigration laws since recent immigrants tended to score lower on the tests. While Yerkes suggested that the tests measured only native intelligence, the questions themselves clearly indicated that education and training had an impact on the results.

Contributions to Psychology

Robert Yerkes contributed greatly to the field of comparative psychology. He founded the first primate research laboratory in the United States and served as its director from 1929 until 1941. The lab was later renamed the Yerkes National Primate Research Center.

His work with John D. Dodson led to the development of what is known as the Yerkes-Dodson Law. This law states that performance increases with arousal, but only up to a certain point. When arousal levels become too high, performance actually decreases.

While Robert Yerkes' use of eugenics to interpret the results of his intelligence tests was incorrect, his work in the field of intelligence testing also left a lasting mark on psychology.

Selected Publications

Yerkes, R. M., Bridges, J. W., & Hardwick, R. S. (1915). A Point Scale for Measuring Mental Ability. Baltimore: Warwick & York.

Yerkes, R. M. (1916). The Mental Life of Monkeys and Apes: A Study of Ideational Behavior. Delmar, NY: Scholars' Facsimiles and Reprints.

Yerkes, R. M. (Ed.) (1921) Psychological Examining in the United States Army. U.S. Government Printing Office.

Yerkes, R. M. (1941). Man-power and military effectiveness: The case for human engineering. Journal of Consulting Psychology, 5(5), 205-209.

Yerkes, R. M. (1943). Chimpanzees: A Laboratory Colony. New York: Johnson Reprint Corporation.

2 Sources
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  1. Yerkes RM, Dodson JD. The relation of strength of stimulus to rapidity of habit-formationJournal of Comparative Neurology and Psychology. 1908;18:459-482. doi:10.1002/cne.920180503

  2. Warne RT, Burton JZ, Gibbons A, Melendez DA. Stephen Jay Gould’s analysis of the Army Beta Test in The Mismeasure of Man: Distortions and misconceptions regarding a pioneering mental test. Journal of Intelligence. 2019;7(1):6. doi:10.3390/jintelligence7010006

Additional Reading
  • Fancher, RE. The intelligence men: Makers of the IQ controversy. New York: W. W. Norton & Company; 1985.

  • Greenwood J. Psychologists go to warBehavioral Scientist. Published May 22, 2017.

  • McGuire, F. (1994). Army alpha and beta tests of intelligence. In: Sternberg RJ, ed. Encyclopedia of Human Intelligence. Vol 1. New York: Macmillan; 1994:125-129.

  • Murchison, C (ed.). (1930). History of Psychology in Autobiography. Vol 2. Worcester, MA: Clark University Press; 1930:381-407.

  • The Editors of Encyclopaedia Britannica. Robert M. Yerkes. Encyclopaedia Britannica. Updated January 30, 2020.

By Kendra Cherry, MSEd
Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."