Experimental studies of animal behavior, pursued for the solution of definite problems of sense, instinct, or habit, frequently yield as by-products interesting and important information concerning individual, sex, species, and race differences. Such observations commonly fail to get recorded because of the primary importance to the observer of the problem on which his attention is focused. In preparing his results for publication he would gladly report everything of significance, were it not that exigencies of time and space render this either impracticable or impossible. It is largely because of our conviction 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 experimental observation, there is always the risk of confusing age, sex, or race differences with those which are truly individual. The casual observer readily overlooks the fact that his pet canaries, kittens, or dogs, differ by several weeks in age or are otherwise not suitable for comparison, for as a naturalist he is less concerned with strict comparability than with that knowledge which will lead to sympathetic insight. 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 individuality. Field naturalists and the born lovers of animals know by intimate acquaintance 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.
Field naturalists and the born lovers of animals know by intimate acquaintance 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 essential points and existing under the same conditions of observation, exhibit surprisingly different modes of response. Thus, one individual adapts itself to the demands of a situation, works smoothly, steadily—as it were willingly; another slowly and haltingly meets the experimenter’s requirements. Its tendency to do the wrong thing seemingly amounts to perversity or stubbornness. And so the observer gains the feeling that the two organisms are quite as different in reactive tendency as are two men.
It has often been remarked that the individuals of a human race with which one is unfamiliar look alike. This we always discover to be due to our failure to notice marked individual differences. As our familiarity with the type increases, these individual traits become increasingly obvious. Now precisely what is true in our experience with our fellow men is still more true of other types of organism. We note at first only the species or racial differences, or perhaps if they be equally conspicuous, certain age and sex differences, but as we continue to live with the organisms and to observe them carefully day by day, we come to appreciate those qualitative and quantitative peculiarities which constitute individuality. As far as we can see, there is no significant difference in degree of individuality between earthworm and man, ant and monkey.
Even in invertebrates individuality becomes conspicuous with familiarity. Among earthworms we have observed that specimens, comparable in all essential points and existing under the same conditions of observation, exhibit surprisingly different modes of response.
Intimacy of relation with a wide range of organic types has served, among other things, to convince us that temperament, character, and genius are terms, which, like individuality, may be used quite as appropriately in connection with one type of organism as with another. We wish especially, in this paper, to report certain of our observations concerning these aspects of life. Temperament we have come to think of as the sum of fundamental, inborn reactive tendencies,—they are sometimes called primary instincts; character, as these same tendencies organized through environmental contact or experience into a complex and more or less highly adaptive system of behavior; genius, as exceptionally strong or well-marked temperamental traits of a particular order. The conventional and ancient classification of temperaments according to strength and duration of response as choleric, melancholic, sanguine, and phlegmatic seems unduly simple in the light of our observations, for there are at least several important ingredients or constituents of temperament which apparently vary independently or in groups with respect to strength and duration of response, and possibly also in other important ways. We may not here further dwell upon definitions, but we shall hope to render these suggestions more significant by the facts which we have to record.
Some years ago we undertook a comparative study of two strains of albino rat, the one closely inbred for many generations, the other outbred. Save for this difference, the individuals of the strains were entirely comparable. We attempted by various experimental means to discover peculiarities of behavior in these animals. Soon it became apparent that the inbred individuals adapted themselves less readily to new environmental demands. They proved less apt pupils in tests of habit formation. We were struck, as our observations progressed, by certain peculiarities of behavior which appeared to be characteristic of the strains rather than of individuals. Among them fear, timidity, savageness, curiosity, sociability were conspicuous. In general, the inbred rats seemed more timid, fearful, more likely to defend themselves by biting if disturbed, One rat is extremely fearful of anything new or unusual, it shrinks timidly from the experimenter. It can only with difficulty be induced to run its way through the experimental apparatus. Another individual of the same age and sex, born in the same litter, is by contrast aggressive and exhibits marked initiative in new situations. less ready to try new things, more suspicious of the experimenter, slower to acquire obviously profitable modes of response than were the outbred animals. These differences in behavior seemed to us to account for an apparent difference in intelligence, and we finally concluded that it is really quite beside the mark to contrast the two strains by saying that the one is the more or the less intelligent.