Individuality, Temperament, and Genius in Animals

Research that lets us appreciate human individuality

Our space will not permit us to recite in detail, as we are tempted to do, the peculiarities which these birds exhibited during a memorable summer. We must content ourselves with the simple statement that in reactions which may be designated as those of wildness, fear, timidity, curiosity, suspicion, initiative, sociability, the individuals differed most obviously and importantly. We hope sometime, in justice to the problem of crow temperament, to devote a summer to the intensive study of sex and individual differences in these extremely intelligent birds.

Concerning temperament, character, and genius in the Primates, our materials are at once abundant and to us absorbing. Everyone who knows anything about primates, high or low, realizes that in them individuality is more conspicuous for the human observer than in most other organisms. But our results do not justify the conclusion that temperamental differences are more obvious or more important in monkeys, anthropoid apes, or man, than in crows, pigs, or rats. We have come to suspect that the popular opinion concerning the matter is due chiefly to similarity of structure and behavior—in a word, to felt kinship. It is simply because we are more like monkeys and apes that we more readily notice and more highly value their individual characteristics.

Not so very long ago, we had a splendid opportunity to become intimately acquainted with two adult male monkeys of the species Pithecus irus [Macaca irus]. The one, we shall call Skirrl; the other, Jimmie. It would be easier to tell what these individuals had in common than to enumerate their differences. Their temperamental divergences constantly amazed us. But here we must content ourselves with an account of a few of the most remarkable differences in behavior.

The monkey was provided with a suitable hammer, nails, and a board. He went to work immediately and although be exhibited no constructive ability, his skill, without tuition, in handling hammer and nails and in driving the latter into the board or elsewhere, according to his taste, more than equaled that of the unpracticed human.

Skirrl’s attitude toward the friendly experimenter was frankly aggressive, but not vicious. Jimmie was extremely vicious; he never could be trusted. Skirrl’s interest in objects which he could play with or in any wise manipulate proved inexhaustible, whereas Jimmie exhibited slight interest in other objects than the members of his species, his enemies, or foods. By a competent observer who had studied him carefully prior to our acquaintance, we were told that Skirrl was feeble-minded. And it certainly seemed so, when, as frequently happened, he sat before an experiment box, yawning repeatedly, and from time to time interrupting these expressions of ennui by half-hearted attempts to solve his problem. Whereas Skirrl rather quickly became accustomed to unusual experimental situations, Jimmie was so wary and distrustful that we finally gave up our attempts to observe his behavior under rigidly controlled conditions, and treated him merely as a visitor in the laboratory.

One day we noticed Skirrl pounding with a stick a nail which he had found in his cage. We were quick to follow this cue. The monkey was provided with a suitable hammer, nails, and a board. He went to work immediately and although be exhibited no constructive ability, his skill, without tuition, in handling hammer and nails and in driving the latter into the board or elsewhere, according to his taste, more than equaled that of the unpracticed human. In the presence of the same outfit of tools, Jimmie threw the hammer into one corner of his cage, scattered the nails about the floor, and proceeded to tear the board to pieces with his teeth. Never did he exhibit the least inclination to use hammer and nails independently or together as tools or implements.

When given a saw, rendered indestructible by metallic guards for the handle, and a heavy wooden block on which the saw might be used, Skirrl was manifestly pleased. He used the saw in quite as many and varied ways as might a boy of four or five years. By sawing before him at various times, the observer tried to teach him to use it in the conventional human way. But to this he paid scant attention, preferring, it seemed, to work out his own modes of amusement. Finally, he hit upon a way of using the saw which we have been told is in vogue among certain peoples of the East. Sitting on the floor, he held it teeth uppermost, his feet grasping the handle tightly and holding the saw firmly in position. He then grasped a nail by both ends and rubbed it rapidly over the teeth of the saw, thus producing a noise which evidently delighted his soul.

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It is clear enough from the responses of other monkeys of the same and opposite sex (the same and other species) to saw, hammer, and nails, as well as to other implements, that Skirrl’s behavior must be described as highly individual or temperamental. Never have we observed anything comparable with it in any untaught Primate other than the human. We have agreed to call Skirrl’s behavior an expression of genius, for the more we consider the matter the more certain we feel that this particular individual possesses remarkably strong tendencies to react to certain objects as tools or mechanical devices. From our point of view, he possesses an unusual type of interest or the same to an unusual degree. Feeble-minded though he may be as far as most intellectual requirements are concerned, he is a genius in mechanical manipulation, and to him we feel indebted for a new point of view and for new insight into the meaning of genius.

The anthropoid apes are so manlike in appearance and behavior that we should be surprised were they not highly individualized and possessed of temperamental traits as well as forms of genius strikingly similar to our own. Our opportunities for intimate acquaintance with the higher apes have been disappointingly few, but with one young orang-utan whom we knew as Julius, we came into delightfully friendly relations. Julius was not born in captivity—few anthropoid apes have that advantage, or disadvantage—but he was captured young, and when we knew him in California, he was probably not far from five years old. Already we have recorded in print many interesting features of his behavior, as well as our strong conviction of the supreme importance to science and to other aspects of civilization of the thorough study of the anthropoid apes.

When threatened with punishment or actually punished, and when, out of sorts or ill, the young orang-utan behaved so like a child of two or three years that he caused the observers to feel uncomfortably sympathetic.

Julius one day was resting placidly in his good-size cage. A workman passing the cage stopped and offered him a banana. He hurried over to get the proffered food, but just as he reached out his hand for it, the man unkindly drew it away and started to walk off. Julius, evidently disappointed and seemingly resentful, turned, and by a series of somersaults rapidly rolled the whole length of his cage. Later, the same sort of behavior was observed in quite different situations. When, for instance, after working persistently to solve an experimental problem, he failed to obtain the desired reward of food, Julius would bring his head to the floor with a thump and turn a few somersaults. In thus expressing his feelings of disappointment and resentment, he seemed to relieve himself, for afterward be would go to work, sometimes with energy and a fair show of cheerfulness. It may be remarked, by the way, that similar modes of response have been observed in children of two to six years of age. We recall an instance in which a little boy who for some time had been working unsuccessfully on an ideational problem bumped his head several times, carefully it is true, against a wooden partition, and then remarked, by way of explanation, that he wished to stir things up.

When threatened with punishment or actually punished, and when, out of sorts or ill, the young orang-utan behaved so like a child of two or three years that he caused the observers to feel uncomfortably sympathetic. Many aspects of his behavior, which unhappily we may not now stop to describe, reminded us of our observations of children, and we found ourselves involuntarily comparing him with human subjects.

How surprising it is, as one stops to reflect on this matter of temperament, that in the same household, as children of the same parents, we find individuals who seem to be opposites in the most varied respects. The one child is sympathetic; the other tends to be cold, unresponsive, or even cruel. The one is frank, naturally honest; the other sly, secretive, and unreliable. The one kindly, good-natured; the other sour and resentful. As these children develop, their temperamental traits may be molded perhaps by educational influences into equally valuable types of character. But never by any chance can they come to possess similar temperamental characteristics.

Surely we shall do well to observe diligently and develop means of studying carefully and measuring the various constituents of temperament, and the factors which enter into character. We should study the constitution and varieties of genius, and especially the conditions which, as experience, operate upon temperamental traits to develop the responses of genius and to elaborate character. For in our efforts to control and direct human life knowledge of those aspects of individuality is of fundamental importance, and there are today unmistakable indications that the future will require of us a science of human behavior which shall consider as carefully the individual as the species. We live in the era of the biological sciences, and we look forward to an unprecedented development of the sciences of organic function, and especially of those which, like physiology, psychology, and sociology, attempt to inform us concerning phenomena of behavior. These sciences promise to become of supreme importance to civilization.


Basset, G. C. “Habit Formation in a Strain of Albino Rats of Less Than Normal Brain Weight.” Behavior Monographs 2: Serial No. 9, 1914.

Coburn, Charles A. “The Behavior of the Crow, Corvus americanus, Aud.” Journal of Animal Behavior 4:185–201, 1914.

Coburn, Charles A., and Robert M. Yerkes. “A Study of the Behavior of the Crow, Corvus americanus, Aud., by the Multiple–Choice Method.” Journal of Animal Behavior 5:75–114, 1915.

Utsurikawa, Nenozo. “Temperamental Differences Between Outbred and Inbred Strains of the Albino Rat.” Journal of Animal Behavior 2:111–129, 1917.

Yerkes, Ada W. “Comparison of the Behavior of Stock and Inbred Albino Rats.” Journal of Animal Behavior 6:267–296, 1916.

Yerkes, Robert M. “The Heredity of Savageness and Wildness in Rats.” Journal of Animal Behavior 3:286–296, 1913.

Yerkes, Robert M., and Charles A. Coburn. “A Study of the Behavior of the Pig, Sus scrofa, by the Multiple–Choice Method.” Journal of Animal Behavior 5:185–225, 1915.

Yerkes, Robert M. “The Mental Life of Monkeys and Apes: A Study of Ideational Behavior.” Behavior Monographs 3: Serial No. 12, 1916.

Yerkes, Robert M. “Provision for the Study of Monkeys and Apes.” Science N. S. 43:231–234, 1916.

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