YERKES, ROBERT MEARNS (1876- 1956)

During his years as a graduate student at Harvard, Yerkes shifted from an early interest in medicine to research on the evolution of behavior from the lowest organisms to man. His first work was done in the laboratory of comparative zoology, and soon after publishing a book entitled The Dancing Mouse (1907), he was appointed to the comparative psychology staff. The book was followed by many apers on a wide range of organisms and, in 1909, by a review in which he and S. Margulis introduced Pavlov’s work to American psychologists. In 1911 he published his Introduction to Psychology, which stressed the importance of a comparative approach to behavior.Yerkes left Harvard to accept an appointment as full professor at the University of Minnesota in 1917, and in the following year became president of the American Psychological Association. When America entered the war he was put in charge of the psychologists who developed the Army intelligence tests, and helped to devise a point scale to be used in testing recruits. He also served as chief of the psychological division of the Surgeon-Gen- eral’s Office and chairman of the Information Service of the National Research Council, later becoming chairman of its Committee on Research in Problems of Sex. In 1924 he accepted the post of research professor at Yale’s Institute of Human Behavior, and established the Yale Laboratories of Primate Biology at Orange Park, Florida. This center fulfilled a dream he had as a graduate student, that of breeding and experimenting on chimpanzees under ideal conditions. His work at the laboratories made him the world’s leading authority on higher primates, and a year after his retirement in 1942, the name was changed to the Yerkes Laboratories in his honor.Yerkes is responsible for a wealth of new information on the mental processes of monkeys and apes. He discovered that chimpanzees will imitate each other and also imitate human beings when they are in situations that capture their interest. He anticipated Kohler in showing that an orang-utan will stack several boxes and stand on them to reach for food, provided he first sees how it is done. He also found that once the problem is learned, the animal can repeat it and transfer the solution to a similar problem.Yerkes combatted the widespread use of instinctual explanations by proving that mouse-killing in kittens is not innate but depends on learning experiences. He developed a “multiple choice” method for testing the mental ability of lower animals by lining up a series of boxes and placing food in one of them. The subject was then tested to see if it could remember that a box placed in a certain position contained food. He also collaborated in formulating the Yerkes-Dodson Law which states that strong motivation usually interferes with learning a difficult discrimination task, but has a positive effect on the learning of easier tasks. As an example, excitement might prevent us from threading a needle but help us with the easier task of picking out a friend in a crowd.