Subsequently, increasingly definite and well-controlled studies were made, in which were recorded observations concerning the preferred position of an individual in its cage or nest box; the relative positions at different hours of the two individuals, male and female, in a given cage; the degree or amount of activity; savageness, or the tendency to bite; and the quickness and amount of response to various stimuli. These and similar observations shortly indicated that savageness designates certain tendencies to reaction, as does also fear, timidity, or wildness, and that our only intelligible way of defining these terms is by enumerating the several types of activity. Wildness, for example, is indicated by attempts to hide in the cage or in the observer’s hand, random and excited running about with repeated attempts to escape, squeaking, and various other forms of response. Timidity, which seemingly is not identical with wildness or fear, involves the avoidance of the experimenter, a kind of chattering or gnashing of the teeth, cowering, or even trembling.
Although most of our studies have been concerned with relations of behavior to inbreeding or to the crossing of individuals which differ markedly in some trait, we have incidentally obtained abundant evidence of important individual differences of the temperamental sort. One rat for example, 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. When cornered, it defends itself by biting the experimenter’s hand. Its wildness is indicated by persistent efforts to hide or to escape. It responds quickly and markedly to any sudden and unexpected stimulus; peculiarly startling stimuli at times cause it to tremble. Another individual of the same age and sex, born in the same litter, is by contrast aggressive and exhibits marked initiative in new situations. Its fear or timidity is readily overcome by its curiosity. It quickly becomes accustomed to the experimenter, and allows him to touch it or take it up in his hand without attempting to bite, and shortly without effort to escape. It responds slowly and only slightly to most stimuli and is disturbed only by strong stimulation. In a word, the two rats are temperamentally as different as any two human beings one is likely to meet. It is such observations as these, made on many different individuals, that have wholly convinced us of the desirability of a careful analysis of temperament and the reduction to terms of measured description of its chief constituents.
We once undertook to study experimentally the ideational behavior of pigs. For this purpose two young animals were chosen, the one a male, the other a female. They were observed daily, and for several hours each day, the whole of one summer. We became sufficiently well acquainted with their characteristics to appreciate alike their varying degrees of intelligence and their temperamental peculiarities. What we have not published in our report on the behavior of these creatures certainly would interest the general reader much more than our printed contribution toward the solution of our problem. We therefore venture to present certain of the fascinating byproducts of our summer’s work. That the differences which we are about to emphasize are not necessarily individual, we readily admit; that they are not age or species differences, we are certain. We expect that some, at least, are sex differences.
Nip and Tuck, for thus we early decided to designate our subjects, soon made us feel their individuality. Both, under the spur of the hunger motive, worked remarkably well toward the solution of ideational problems, and their success in this work fully justified the popular impression that the pig is one of the more intelligent among mammals. Nip, the male, was less active and energetic than his sister, Tuck. He also was less greedy, and showed rather less initiative and a more limited range of reactions. Tuck it was who usually led if there was opportunity for competition, while Nip followed. Both quickly became accustomed to the experiment, but Nip showed more persistent wariness, timidity, and suspicion than did Tuck. She, however, was much quicker in response, more alert, curious, and quick to discover new opportunities for pig satisfaction. When at work on experimental problems, Nip much more easily discouraged and tended earlier than Tuck to give up his search for the reward of success. Tuck constantly acquired new and profitable tricks, which as a rule sooner or later appeared in Nip also, sometimes spontaneously and again by reason of the imitative tendency.
One summer we removed a brood of four young crows from their nest just before they were able to fly. We could not identify the sexes at the time, so the differences we observed may be either sex or individual, but at any rate, the four specimens were as sharply contrasted in temperament as are the children of any household.
As day after lay we observed these two specimens of a mammalian type whose life under domestication gives its intelligence slight opportunity for display, we were strongly impressed, as we had been in the case of rats also, by the importance of temperamental reactive tendencies in responses to any experimentally arranged situation. The experimenter who ignores individuality or temperament in his subjects runs a grave risk of misunderstanding or wrongly evaluating his results. Our descriptions sound anthropomorphic, but that, the alert reader will appreciate, is due to our avoidance of stilted and unnatural terminology. We are attempting to describe in an intelligible way, and briefly, behavior which, if we should restrict ourselves to wholly objective terms, would require pages of unusual behavioristic statement.
Among the birds, there is probably no more interesting object of study than the crow. Its species characteristics are notably alluring to the psychologist, but to us, as a result of varied observations in the corn fields of Pennsylvania and on the wooded hills of New Hampshire, sex, age, and individual differences are no less fascinating. One summer we removed a brood of four young crows from their nest just before they were able to fly. We could not identify the sexes at the time, so the differences we observed may be either sex or individual, but at any rate, the four specimens were as sharply contrasted in temperament as are the children of any household.
We set about rearing these birds by hand, the while taming them for experimental purposes. Within a few days, one of the four began to exhibit the characteristic fear reaction of its species, and at once it became extremely difficult to feed. For a few days we persisted in our attempts, and then as he or she, as the case may have been, was no less persistent, we decided to devote our time and energies to his three companions. Thus, at the very outset, temperamental peculiarities, perhaps amounting to nothing more than exceptionally strong and persistent fear reactions, served to eliminate one of the individuals from our collection.