Individuality, Temperament, and 

 Genius in Animals 



FROM SUCH RESEARCH WE LEARN TO APPRECIATE HUMAN INDIVID- 

 UALITY. AND TO REALIZE THAT ANY FUTURE CONSCIOUS CON- 

 TROL OF HUMAN LIFE MUST COME THROUGH A STUDY OF 

 THE CONDITIONS UNDER WHICH VARIED TYPES OF 

 TEMPERAMENT WILL DEVELOP THE HIGHEST 

 CHARACTER AND THE GREATEST GENIUS 



Bv ROBERT M. YERKES^ and ADA AV. YERKES 



EXPERIMEXTAL studies of ani- 

 mal behavior, pursued for the 

 solution of definite problems of 

 sense, instinct, or habit, frequently 

 yield as by-products interesting and 

 important information concerning in- 

 dividual, sex, species, and race differ- 

 ences. Such observations commonly 

 fail to get recorded because of the pri- 

 mary importance to the observer of the 

 problem on which his attention is fo- 

 cused. In preparing his results for 

 publication he would gladly report 

 everything of significance, were it not 

 that exigencies of time and space ren- 

 der this either impracticable or impos- 

 sible. It is largely because of our con- 

 viction that certain of the unrecorded 

 by-products of our investigations are in 

 various respects more important than 

 the data which we have published, that 

 we are attempting to write on evidences 

 of individuality in various organisms. 

 In this field of naturalistic and ex- 

 perimental observation, there is always 

 the risk of confusing age, sex, or race 

 differences with those which are truly 

 individual. The casual observer read- 

 ily overlooks the fact that his pet ca- 

 naries, kittens, or dogs, differ by sev- 

 eral weeks in age or are otherwise not 

 suitable for comparison, for as a natu- 



ralist he is less concerned with strict 

 comparability than with that know- 

 ledge which will lead to sympathetic in- 

 sight. But to those who are trained in 

 critical and well-controlled observation, 

 it is an easy task to eliminate such 

 sources of error and to obtain fairly 

 comparable data concerning individual- 

 ity. Field naturalists and the born lov- 

 ers of animals know by intimate ac- 

 quaintance that important individual 

 differences exist in many species of 

 organism, but experimentalists are less 

 generally aware of this fact, for their 

 attention tends to be monopolized by 

 problems of species characteristics and 

 of general organic functions or reactive 

 capacity. 



Even in invertebrates individuality 

 becomes conspicuous with familiarity. 

 Among earthworms we have observed 

 that specimens, comparable in all essen- 

 tial points and existing under the same 

 conditions of observation, exhibit sur- 

 prisingly different modes of response. 

 Thus, one individual adapts itself to 

 the demands of a situation, works 

 smoothly, steadily — as it were will- 

 ingly; another, slowly and haltingly 

 meets the experimenter's requirements. 

 Its tendency to do the wrong thing 

 seemingly amounts to perversity or 



^ Dr. Robert M. Yerkes is assistant professor of comparative psychologj- at Harvard University, man- 

 aging editor of the Journal of Animal Behavior, and editor of the Animal Behavior Series. 



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