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Robert Yerkes

1876-1956
American psychologist who made important contributions to the fields of comparative animal psychology, particularly in the areas of animal intelligence and behavior.

Robert Yerkes was born in Pennsylvania, and was educated at Harvard University, where he received his doctorate in psychology in 1902. He served as professor of psychology at Harvard, the University of Minnesota, and Yale University, and as a member of the National Research Council. In 1919, Yerkes founded the Yale Laboratories of Primate Biology and served as its director from 1929 to 1941, when the lab was moved to Orange Park, Florida. A year later, it was renamed the Yerkes Laboratories of Primate Biology. A pioneer in the field of comparative psychology, Yerkes studied the intelligence and behavior of many forms of animal life, from jellyfish to humans, but he focused most of his attention on primates. Among his findings were the discovery that chimpanzees imitate both each other and human beings, and the observation that orangutans can pile boxes on top of one another to reach food after seeing this demonstrated, thus transferring this experience to other learning problems.

Yerkes also worked on the Yerkes-Dodson Law, which states that for every task there is an optimum level of motivation, and that motivation that is too strong can actually interfere with the ability to perform a difficult task. Yerkes also pioneered the use of monochromatic light to study color vision in animals. In 1911, he developed the first multiple-choice test for animals, designed to test abstraction abilities. A row of nine or fewer boxes were shown to the animal, which had to determine which of the open boxes had food in it and then remember that box in subsequent rounds of testing.

Turning his attention to human testing, Yerkes revised the Stanford-Binet Intelligence scales in 1915 to create a widely used point scale for the measurement of

Robert Mearns Yerkes (The Library of Congress. Reproduced with permission.)

human mental ability. He was also a principal figure in the development of human multiple choice testing. During World War I, Yerkes directed a team of 40 psychologists charged with assessing the abilities of army recruits for training, assignment, and discharge purposes. Together they developed the Army Alpha test, a written intelligence test, and Army Beta, a pictorial test for the 40 percent of draftees who were functionally illiterate. By the end of the war, these tests had been used to classify some 1.75 million men. As a result of taking these tests, some 8,000 had been discharged as unfit, while the Alpha test played a role in the selection of two thirds of the 200,000 men who served as commissioned officers during the war.

In addition to its impact on the military, the wartime testing developed by Yerkes and his colleagues had a farreaching effect on civilian life after the war. Unlike the Stanford Binet scale, which had to be individually administered by a tester, the Alpha and Beta tests were developed to be administered to groups, making them faster, simpler, and far less expensive to use. After the war, this breakthrough in mental measurement led to a dramatic expansion in intelligence testing. Yerkes and several colleagues devised one of several pencil-and-paper tests that were marketed to school administrators throughout the country. The National Research Council, the test's sponsor, described it as deriving from "the application of the army testing methods to school needs." By 1930, it had been administered to seven million schoolchildren. (The Scholastic Aptitude Test was developed by one of Yerkes' colleagues during this same period.) Yerkes' books include: Introduction to Psychology (1911), The Mental Life of Monkeys and Apes (1916), The Great Apes (1929) (coauthored with Ada Yerkes), and Chimpanzees: A Laboratory Colony (1943).

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