Robert Mearns Yerkes

“ We have here an expression of the tendency to the repetition of an act. It is only after an animal acquires considerable familiarity with a situation that it begins to vary its behavior in accordance with relatively unimportant factors in the situation. It is this fact, illustrations of which may be seen in human life, as well as throughout the realm of animal behavior, that renders it imperative that an animal be thoroughly acquainted with the apparatus for experimentation and with the experimenter before regular experiments are begun. ”

“ I conclude from my experimental study of vision that although the dancer does not possess a color sense like ours, it probably discriminates the colors of the red end of the spectrum from those of other regions by difference in the stimulating value of light of different wave lengths, that such specific stimulating value is radically different in nature from the value of different wave lengths for the human eye, and that the red of the spectrum has a very low stimulating value for the dancer. ”

“ If a dancer which knows how to escape to the cage by way of the ladder be placed in the wooden box with one which, despite abundant opportunity, has proved unable to form the habit on his own initiative, will the latter profit by the activity of the former and thus learn the method of escape? ”

“ That this inference of functional facts from structural conditions is correct I am by no means certain, but at any rate all of the experiments which I have made to determine the visual ability of the dancer go to show that color vision, if it exists at all, is extremely poor. It is gratifying indeed to learn, after such a study of behavior as has just been described, that the structural conditions, so far as we are able to judge at present, justify the conclusions which have been drawn. ”

“ If my time and attention had not been fully occupied with other problems, I should have determined the efficiency of various methods of training in terms of the duration of habit, as well as in terms of the rapidity of its formation. As these two measures of efficiency might give contradictory results, it is obvious that a training method cannot be fairly evaluated without consideration of both the rapidity of habit formation and the permanency of the habit. A priori it seems not improbable that slowness of learning should be directly correlated with a high degree of permanency. ”

“ From my own experience in the use of the labyrinth with the dancer and with other animals, I am forced to conclude that its chief value lies in the fact that it enables the experimenter so to control the factors of a complex situation that he may readily determine the importance of a given kind of sense data for the formation or the execution of a particular habit. ”

“ As I shall hope to make clear in a subsequent discussion of the dancer's peculiarities of behavior, in a chapter on individual differences, there is no sufficient reason for doubting the general truth of Cyon's description, although there is abundant evidence of his inaccuracy in details. If, for the present, we accept without further evidence the statement that there is more than one variety of dancer, we shall be able to account for many of the apparent inaccuracies of description which are to be found in the literature on the animal. ”

“ I have quoted his description as an illustration of the weakness which is characteristic of most popular accounts of animal behavior. It proves that it is not sufficient to watch and then describe. The fact is that he who adequately describes the behavior of any animal watches again and again under natural and experimental conditions, and by prolonged and patient observation makes himself so familiar with his subject that it comes to possess an individuality as distinctive as that of his human companions. ”

“ Very early in my study of the dancer, I learned that a single experience in a given experiment day after day had so little effect upon the animal that a perfect habit could not be established short of several weeks or months. Similarly, experiments in which two tests per day were given proved that even a simple discrimination habit cannot be acquired by the animal under this condition of training with sufficient rapidity to enable the experimenter to study the formation of the habit advantageously. ”

“ Finally, when the mouse runs first to one box and then to the other, and repeats this anywhere from one to fifty times, the choice may be described as comparison of the boxes; therefore, I call it choice by comparison. Certain individuals choose first by comparison, and later almost uniformly by affirmation and negation. Whenever the conditions are difficult to discriminate, choice by comparison occurs most frequently and persistently. ”

“ The casual observer of the dancer gets an impression that it turns to the left more often than to the right; he verifies his observation a few times and then asserts with confidence that such is the truth about turning. That such a method of getting knowledge of the behavior of the animal is worse than valueless is clear in the light of the results of the systematic observations which have just been reported. ”

“ In writing this account of the dancing mouse I have attempted to lay as much stress upon the development of my methods of work as upon the results which the methods yielded. In fact, I have used the dancer as a means of exhibiting a variety of methods by which the behavior and intelligence of animals may be studied. As it happens the dancer is an ideal subject for the experimental study of many of the problems of animal behavior. It is small, easily cared for, readily tamed, harmless, incessantly active, and it lends itself satisfactorily to a large number of experimental situations. ”

“ The females, especially during periods of sexual excitement, are much more likely to squeak than the males. At such times they give their shrill cry whenever they are touched by another mouse or by the human hand. A slight pinching of the tail will frequently cause the female to squeak, but the male seldom responds to the same stimulus by crying out. The most satisfactory way to demonstrate the existence of a voice in the male is to subject him to the stimulating effect of an induced current, so weak that it is barely appreciable to the human hand. ”

“ For it appears that a pair of mice dancing together, or near one another, sometimes collide, and that it is only those holes with which the animal is familiar that are entered skillfully. In fact, the longer one observes the behavior of the dancer under natural conditions, the more he comes to believe in the importance of touch, and motor tendencies. Sight, which at first appears to be the chief guiding sense, comes to take a secondary place. In this chapter it is my purpose to show by means of simple experiments what part sight plays in the dancer's life of habit formation. ”

“ The dancing, waltzing, or circus course movement, as it is variously known, varies in form from moment to moment. Now an individual moves its head rapidly from side to side, perhaps backing a little at the same time, now it spins around like a top with such speed that head and tail are almost indistinguishable, now it runs in circles of from 5 cm. to 30 cm. in diameter. If there are any objects in the cage about or through which it may run, they are sure to direct the expression of activity. A tunnel or a hole in a box calls forth endless repetitions of the act of passing through. ”

“ I propose in this chapter to present certain facts concerning the inheritance of individual peculiarities of behavior, and to state the results of a series of experiments by which I had hoped to test the inheritance of individually acquired forms of behavior.
My study of the nature of the whirling tendency of the dancer has revealed the fact that certain individuals whirl to the right almost uniformly, others just as regularly to the left, and still others now in one direction, now in the other. ”

“ But from my experiments it has become apparent that the average of the results given by five individuals of the same sex, age, and condition of health, when kept in the same environment and subjected to the same experimental tests, is sufficiently constant from group to group to warrant its use as an index of modifiability for the race. This expression, index of modifiability, is a convenient mode of designating the average number of tests necessary for the establishment of a perfect habit of white-black discrimination. ”

“ Usually in experiments with mammals hunger has been the motive depended upon. The animals have been required to follow a certain devious path, to escape from a box by working a button, a bolt, a lever, or to gain entrance to a box by the use of teeth, claws, hands, or body weight and thus obtain food as a reward. There are two very serious objections to the use of the desire for food as a motive in animal behavior experiments—objections which in my opinion render it almost worthless in the case of many mammals. ”

“ Too frequently investigators, in their work on vision in animals, have assumed that brightness vision and color vision are inseparable; or, if not making this assumption, they have failed to realize that the same wave-length probably has markedly different effects upon the retinal elements of the eyes of unlike organisms. In a study of the sense of sight it is extremely important to discover whether difference in the quality, as well as in the intensity, of a visual stimulus influences the organism; in other words, whether color sensitiveness, as well as brightness sensitiveness, is present. ”

“ So far as I have been able to learn, no investigator has carefully examined the brain and spinal cord in comparison with those of the common mouse, and only those who have failed to find any structural basis for the facts of behavior in the organs of the ear have attempted to account for the dancer's whirling and deafness by assuming that the cerebellum is unusual in structure. We are, therefore, forced to conclude that our knowledge of the nervous system of the dancing mouse does not at present enable us to explain the behavior of the animal. ”

“ It is fairly certain that individuals with a tendency to move in circles appear at rare intervals in races of common mice. It seems highly probable, in view of these facts, that the Chinese took advantage of a deviation from the usual form of behavior to develop by means of careful and patient selectional breeding a race of mice which is remarkable for its dancing. Even if it should be proved that the mutation as it appears among common mice is not inherited, the view that slight deviations were taken advantage of by the breeders would still be tenable. ”

“ Several times I have observed nests so poorly built that almost all of the young perished because they got too far away to find their way back to the mother. It is surprising that the female should not take more pains to keep her young safe by picking them up in her mouth, as does the common mouse, and carrying them to a place where they can obtain warmth and nourishment. This I have never seen a dancing mouse do. For the first day or two after the birth of a litter the female usually remains in the nest box almost constantly and eats little. ”

“ It must have room to dance. This furnished a sufficiently strong motive for the entering of the electric-boxes. It must avoid disagreeable and unfavorable stimuli. This is a basis for attempts to choose, by visual discrimination, the electric-box in which the shock is not given. It may safely be said that the success of the majority of the experiments of this book depended upon three facts: (1) the dancer's tendency to avoid disagreeable external conditions, (2) its escape-from-confinement- impelling need of space in which to dance freely, and (3) its abundant and incessant activity. ”

“ Evidently the dancer is exceptionally strong in certain respects, although it may be weak in others. Such general statements as are usually made fail to do justice to the facts.
The supposition that light determines the periodicity of dancing is not borne out by my observations, for I have found that the animals continue to dance most vigorously toward evening, even when they are kept in a room which is constantly illuminated. In all probability the periodicity of activity is an expression of the habits of the mouse race rather than of the immediate influence of any environmental condition. ”

“ A brief description of the behavior of the dancer in the brightness discrimination experiments which have been described may very appropriately form the closing section of this chapter. For the experimenter, the incessant activity and inexhaustible energy of the animal are a never-failing source of interest and surprise. When a dancer is inactive in the experiment box, it is a good indication either of indisposition or of too low a temperature in the room. In no animal with which I am familiar is activity so much an end in itself as in this odd species of mouse. ”

“ For three years my mice have bred frequently and reared almost all of their young. During one year, after I had learned how to care for the animals, when the maximum number under observation at any time was fifty and the total number for the year about one hundred, I lost two by disease and one by an accident. I very much doubt whether I could have done better with any species of mouse. There can be no doubt, however, that the dancer is delicate and demands more careful attention than do most mice. ”

“ In the prime of its life (from the second to the tenth month) the dancer is active, full of energy, quick to learn; in its senility (during the second year) it is inactive, but at times even more docile than during the period of greatest physical development. Frequently I have noticed in connection with labyrinth tests that individuals of the age of a year or more learn much more quickly than do individuals of the age of two or three months. But, on the other hand, I have contradictory observations, for now and then I obtained just the opposite result in experiments to test docility. ”

“ My observations of differences in sensitiveness to other forms of stimulation were made in connection with training tests, and although they are not quantitative, I venture to call attention to them. Indeed, I am led by the results of my study of various aspects of the dancer's behavior to conclude that the race exhibits individual differences in discriminating sensitiveness to a far greater extent than do most mammals, not excepting man. ”

“ To this query Rawitz has replied that the lack of certain senses compels the animal to strive through varied movements to use to the greatest advantage those senses which it does possess. In Rawitz's opinion the lack of hearing and orientation is compensated for by the continuous use of sight and smell. The mouse runs about rapidly, moves its head from side to side, and sniffs the air, in order that it may see and smell as much as possible. In support of this interpretation of the restlessness of the dancer, Rawitz states that he once observed similar behavior in an albino dog which was deaf. ”