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Yerkes, Robert M.

Yerkes, Robert M.



Robert Mearns Yerkes (1876-1956) described himself as a “psychobiologist,” a term he used to pinpoint the scientific disciplines that guided his work. His contributions to his self-named field were outstanding; in retrospect, however, his contributions to the development of psychology as a profession, rather than to the science as such, appear to have been even more far-reaching.

Yerkes was born on a prosperous farm in Bucks County, Pennsylvania. He enjoyed observing flowers and birds; he kept as pets both wild and domestic animals. As he grew older, he became progressively disenchanted with working on the farm, considering it a challenge to perform the irksome farm tasks with the minimum effort possible and with the simplest procedure. Farming interfered with his major interest—obtaining an education; he recalled staying home from school to help on the farm and keeping up with his classmates by studying late at night. He always carried a pocket dictionary and studied it during free minutes in the fields or barn, thus mastering vocabulary, spelling, and pronunciation.

The positive influences in his early years were his mother, whom he described as sweet of disposition, wise, and unusually able; a capable young German hired man, possessed of good sense and understanding; and his maternal grandfather, who encouraged his intellectual interests. His father was an industrious worker but unlike his son intellectually; he instilled fear, and later strong resentment and dislike, as did Yerkes’ paternal grandfather. The negative feelings Yerkes harbored toward them doubtless strengthened his determination to avoid farming and to succeed against odds in achieving an education.

Yerkes made his first career choice, medicine, when he was ill with scarlet fever at the age of seven, and he planned a medical career until the early part of his graduate studies. The choice was encouraged by a kindly cousin, the family doctor, who took him to Philadelphia to visit hospitals and physicians at work. After seven years in a country school and one year in normal school in West Chester, Pennsylvania, he would have “read” medicine with his cousin and entered Jefferson Medical College had not a physician uncle in Collegeville offered him a chance to earn his way through Ursinus College. Yerkes eagerly accepted, spending one year at the academy and four years at the college, where the biologist-physician P. C. Mensch aroused his interest in research. After graduation he entered Harvard as a provisional undergraduate, and at the end of a year there he received an A.B. degree. He then faced the decision of entering either medical school or graduate school.

The offer of an assistantship and scholarship led him to choose graduate school. He studied zoology for one year and psychology for two, receiving his doctorate in psychology in 1902 and then remaining as instructor and professor at Harvard until 1917. The transfer from zoology, where he worked with such brilliant men as Edward L. Mark, George H. Parker, Charles B. Davenport, and William E. Castle, to psychology was not a drastic shift, for he was primarily interested in animal psychology. This was generally a golden period for Harvard in the division of philosophy, ethics, and psychology, and Yerkes profited from the presence of Josiah Royce, George H. Palmer, William James, Hugo Münsterberg, Francis Peabody, George Santayana, Dickinson Miller, William McDougall, Edwin B. Holt, and Ralph Barton Perry.

Early in his career, in 1905, he married Ada Watterson. He wrote of his marriage as a partnership “which perfectly blended our lives and incalculably increased our professional and social usefulness” (1932, p. 391). He and his wife collaborated on various papers and on the book The Great Apes (1929).

While still a graduate student, Yerkes conceived the idea of an institute of comparative psychobiology and soon thereafter went to Germany and Switzerland to learn about the organization and equipment of psychological and physiological institutes. For almost three decades he clung tenaciously to his idea and worked hard to promote it, finally bringing it to fruition in 1930, when the Yale (later Yerkes) Laboratories of Primate Biology at Orange Park, Florida, were opened.

In the intervening years Yerkes engaged in a wide variety of projects. He published papers on subjects ranging from jellyfish to apes, from sensation to ideation. His first book was The Dancing Mouse (1907), a comprehensive series of investigations of this distinct breed. He wrote an Introduction to Psychology (1911) at the same time he was teaching summer and extension courses and classes at Radcliffe to supplement his salary. He worked with Edward Thorndike at the Marine Biological Laboratory at Woods Hole, Massachusetts, and collaborated with John Watson on methods for the comparative study of vision in animals (1911) [see Thorndike; Watson]. He studied neurosurgery with Harvey Cushing at Johns Hopkins University. With Gilbert V. Hamilton he developed the multiple-choice method of testing. During a sabbatical leave in 1914-1915, he worked with monkeys and an orangutan in Hamilton’s Montecito laboratory, and this experience intensified his desire for a primate laboratory; in 1916 he published a plan for one, under the title “Provision for the Study of Monkeys and Apes,” but no one volunteered financial support. From 1912 to 1917 he worked half-time as a psychologist at Boston Psychopathic Hospital, became interested in comparative research in psychopathology and in tests and measurements as an aid to psychiatry, and developed with James W. Bridges and Rose S. Hardwick a point scale for measuring mental ability (1915). This last achievement probably had more influence on psychology during the next decades than any other of his projects, for it was the starting point for the development of the Army Alpha.

The year 1917 was an important one for Yerkes. He resigned from his professorship at Harvard and from his hospital post to accept the chairmanship of the department of psychology at the University of Minnesota. He had become disenchanted with Harvard and was excited by the opportunity to develop both the department and the psychology laboratory at Minnesota. The war intervening before he occupied the chair, he directed the department in absentia for two years, during which he effected many changes.

Soon after the outbreak of war in 1917, Yerkes became a major in the Army Medical Department. He and a group of colleagues who believed that psychology could be useful to the war effort had established relations with that department and within 18 months developed the Army Alpha, promoted it against overwhelming odds, and had it accepted. Once they had overcome military and civilian resistance to the test, they trained officers and enlisted men in its administration and tested more than 1.7 million soldiers in 35 army camps. The program ended abruptly with the armistice, but the test had proved its usefulness, assuring psychology a fixed place in the military establishment. Moreover, the results constituted the largest intelligence test sample to that date and provided further impetus to the development of group tests.

After the war Yerkes resigned his Minnesota post and accepted an appointment with the National Research Council in Washington, D.C., seeing this move as the best method both for publishing the results of the army testing program and for finding support for a primate institute. He was unable to realize the latter aim, but he did publish the war materials (1919; 1920; 1921). He firmly established the place of psychology in the National Research Council and the National Academy of Sciences, and he promoted and facilitated grants for research on sex and human migration.

Yerkes bought his first chimpanzees in 1923, housing them in his Washington home. With Blanche Learned, he published the results of his observations in Chimpanzee Intelligence and Its Vocal Expressions (1925). In 1924 he left the National Research Council to become a professor at the new Institute of Psychology at Yale: James R. Angell, the president of Yale, promised Yerkes that he could devote himself to comparative psycho-biology and seek aid for an ape research center. He was, indeed, finally able to obtain such aid. With Carnegie funds, he spent the summer of 1924 studying a private primate colony in Cuba. The following year he received a Rockefeller grant for a pilot laboratory in New Haven and for several chimpanzees; he hoped thereby to demonstrate the feasibility of a larger laboratory in a warm climate. In three successive winters he also studied a gorilla in Florida and published his findings in three monographs (1927; 1928).

In 1930 his dream at last materialized: financed by the Rockefeller Foundation, the Yale Laboratories of Primate Biology, stocked with chimpanzees, opened. Yerkes directed the laboratories until his retirement in 1941 and then went back to New Haven to continue teaching until 1944. During his Yale years, his laboratories published 214 papers, and he produced his two greatest books, The Great Apes (1929) and Chimpanzees (1943).

During World War II he was chairman of the Survey and Planning Committee of the National Research Council’s Emergency Committee in Psychology. One outcome of the committee’s work was the amalgamation of psychological organizations into an enlarged American Psychological Association; many years earlier, in 1917, Yerkes had served that association as president. In his last years he renewed his interest in the gorilla and promoted research on it at the San Diego Zoo; he also wrote his still unpublished “Testament,” an autobiographical manuscript. The last of the ten items in the “personal creed” at the end of his “Testament” fittingly characterizes Yerkes: it is his belief in “the priority of life over death, effort over prayer, knowledge over faith, and resolution over wishfulness.”

Harry F. Harlow

[For discussion of the subsequent development of Yerkes’ ideas, seeIntelligence and Intelligence Testing; Psychology, article On Comparative Psychology; Sexual Behavior, article on Animal Sexual Behavior; Social Behavior, Animal.]


1907 The Dancing Mouse: A Study in Animal Behavior. New York: Macmillan.

1911 Introduction to Psychology. New York: Holt.

1911 Yerkes, Robert M.; and Watson, John B. Methods of Studying Vision in Animals. Behavior Monographs 1, no. 2.

(1915) 1923 Yerkes, Robert M.; and Foster, JosephineA Point Scale for Measuring Mental Ability. Rev. ed. Baltimore: Warwick & York. → Yerkes, J. W. Bridges, and R. W. Hardwick wrote first edition.

1916 Provision for the Study of Monkeys and Apes. Science 43:231-234.

1919 Report of the Psychology Committee of the National Research Council. Psychological Review 26:83-149.

1920 Yoakum, Clarence S.; and Yerkes, Robert M. Army Mental Tests. New York: Holt.

1921 Yerkes, Robert M. (editor) Psychological Examining in the United States Army. Volume 15 of National Academy of Sciences, Memoirs. Washington: Government Printing Office. 1925 Yerkes, Robert M.; and Learned, Blanche W. Chimpanzee Intelligence and Its Vocal Expressions. Baltimore: Williams & Wilkins.

1927 The Mind of a Gorilla. Parts 1, 2. Genetic Psychology Monographs 2:1-193, 375-551.

1928 The Mind of a Gorilla. Part 3. Comparative Psychology Monographs 5, no. 2:1-94.

(1929) 1945 Yerkes, Robert M.; and Yerkes, Ada W. The Great Apes. New Haven: Yale Univ. Press.

1932 Robert Mearns Yerkes: Psychobiologist. Volume 2, pages 381-407 in A History of Psychology in Autobiography. Worcester, Mass.: Clark Univ. Press.

1943 Chimpanzees: A Laboratory Colony. New Haven: Yale Univ. Press; Oxford Univ. Press.


Boring, Edwin G. 1956 Robert Mearns Yerkes: 1876-1956. Pages 133-140 in American Philosophical Society, Yearbook. Philadelphia: The Society.

Carmichael, Leonard 1957 Robert Mearns Yerkes. Psychological Review 64:1-7.

Elliott, R. M. 1956 Robert Mearns Yerkes: 1876-1956. American Journal of Psychology 69:487-494.


See Adolescence; Age Differentiation; Delinquency; Developmental Psychology; Labor Force, article on Participation; Life Cycle.

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