The Dancing Mouse - A Study in Animal Behavior
by Robert M. Yerkes
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As I have on hand results for ten individuals of the age of one month, and for four individuals of the age of four months, it has seemed desirable to state the problem, method, and incomplete results of this study of the relation of modifiability to age. The indices of modifiability for these two groups of dancers differ so strikingly that I feel justified in persisting in my efforts to obtain comparable data for the seven ages which have been mentioned.



Number of Errors in Successive Daily Series of Ten White-Black Tests, with Dancers Four Months Old


NO. 76 NO. 78 AV. NO. 75 NO. 77 AV. GENERAL AV.

A 7 7 7.0 4 8 6.0 6.50 B 8 6 7.0 6 5 5.5 6.25

1 5 5 5.0 5 5 5.0 5.00 2 5 4 4.5 2 2 2.0 3.25 3 4 5 4.5 2 5 3.5 4.00 4 3 4 3.5 1 1 1.0 2.25 5 5 2 3.5 0 1 0.5 2.00 6 3 2 2.5 1 0 0.5 1.50 7 2 1 1.5 1 2 1.5 1.50 8 5 1 3.0 0 0 0 1.50 9 1 3 2.0 0 0 0 1.00 10 1 2 1.5 1 0 0.5 1.00 11 1 1 1.0 0 0 0.50 12 1 1 1.0 0 0 0.50 13 0 0 0 0 0 0 14 0 0 0 0 15 0 0 0 0

The detailed results for the one-month old individuals appear in Table 43; those for the four-month individuals in Table 52. The general averages for the former are to be found in the third column of Table 46, under the heading "10 tests per day"; those for the latter in the last column of Table 52. Mere inspection of these tables reveals the curious sex difference which goes far towards justifying the presentation of this uncompleted work. The index of modifiability for the ten one-month individuals is 88 (that is, 88 tests were necessary for the establishment of a habit); for the four-month individuals it is 102.5. The heavy solid line of Figure 33 joins the points on the ordinates at which these values are located. Apparently, then, the dancer acquires the white-black discrimination habit less readily at the age of four months than at the age of one month.

Further analysis of the results proves that this statement is not true. When the averages for the two sexes are compared, it appears that the males learned much less quickly at four months than at one month, whereas just the reverse is true of the females. The dash and dot line of the figure extends from the index of modifiability of the one-month males (72) to that of the four-month males (120); and the regularly interrupted line similarly joins the indices of the one-month (104) and the four-month (85) females. In seeking to discover age differences in docility or ability to profit by experience we have stumbled upon what appears to be an important sex difference. Perhaps I should add to this presentation of partial results the following statement. Since there are only four individuals in the four-month group, two of each sex, the indices are not very reliable, and consequently too much stress should not be laid upon the age and sex differences which are indicated.

In view of this impressive instance of the way in which averages may conceal facts and lead the observer to false inferences, I wish to remark that my study of the dancer has convinced me of the profound truth of the statement that the biologist, whether he be psychologist, anthropologist, physiologist, or morphologist, should work with the organic individual and should first of all deal with his results as individual results. Averages have their place and value, but to mass data before their individual significance has been carefully sought out is to conceal or distort their meaning. Too many of us, in our eagerness for quantitative results and in our desire to obtain averages which shall justify general statements, get the cart before the horse.

Figure 33 presents the beginning of what I propose to call plasticity curves. When these three curves are completed on the basis of experiments with five dancers of each sex for each of the ages indicated on the base line of the figure, they will indicate what general changes in plasticity, modifiability of behavior, or ability to learn (for all of these expressions have been used to designate much the same capacity of the organism) occur from the first month to the nineteenth in the male and the female dancer, and in the race without respect to sex. So far as I know, data for the construction of plasticity curves such as I hope in the near future to be able to present for the dancing mouse have not been obtained for any mammal.

At present it would be hazardous for me to attempt to state any general conclusion concerning the relation of docility to age.

The initiative of the dancer certainly varies with its age. In scope the action system rapidly increases during the first few months of life, and if the animal be subjected to training tests, this increase may continue well into old age. The appearance of noticeable quiescence does not necessarily indicate diminished initiative. Frequently my oldest mice have shown themselves preeminent in their ability to adjust their behavior to new conditions. However, I have not studied individuals of more than eighteen months in age. One would naturally expect initiative to decrease in senility. All that I can say is that I have seen no indications of it.

We may now briefly consider the principal sex differences which have been revealed by the experiments. In sensitiveness I have discovered no difference, but it should be stated that no special attention has been given to the matter. In docility the males usually appeared to be superior to the females. This was especially noticeable early in my visual discrimination tests. The males almost invariably acquired a perfect habit quicker than the females. I may cite the following typical instances. Number 14 acquired the black-white habit with 40 tests; No. 13, with 60 (Table 10, p. 109). Of the five pairs of individuals whose records in white-black training appear in Table 43, not one contradicts the statement which has just been made. It is to be noted, however, that under certain conditions of training, for example, 20 tests per day, the female is at an advantage. Recently I have with increasing frequency obtained measures of docility which apparently favor the female. That this difference in the results is due to a difference in age is probable.

In labyrinth tests the female is as much superior to the male as the male is to the female in discrimination tests. From the tables of Chapter XIII I may take a few averages to indicate the quantitative nature of this difference. A degree of proficiency in labyrinth B attained by the males after 7.0 trials was equaled by the females after 6.2 trials. In labyrinth C the males acquired a habit as a result of 18.7 trials; the females, as a result of 13.8. And similarly in labyrinth D, 6.1 trials did no more for the males than 5.9 did for the females.

That at the age of about one month the male dancer should be able to acquire a visual discrimination habit more rapidly than the female, whereas the female can acquire a labyrinth habit more readily than the male, suggests an important difference in the nature of their equipment for habit formation. One might hazard the suggestion that the male depends more largely upon discrimination of external conditions, whereas the female depends to a greater extent than does the male upon the internal, organic changes which are wrought by acts. At any rate the female seems to follow a labyrinth path more mechanically, more accurately, more easily, and with less evidence of sense discrimination than does the male.

Finally, in concluding this chapter, I may add that in those aspects of behavior which received attention in the early chapters of this volume the dancers differ very markedly. Some climb readily on vertical or inclined surfaces to which they can cling; others seldom venture from their horizontally placed dance floor. Some balance themselves skillfully on narrow bridges; others fall off almost immediately. My own observations, as well as a comparison of the accounts of the behavior of the dancer which have been given by Cyon, Zoth, and other investigators, lead me to conclude that there are different kinds of dancing mice. This may be the result of crosses with other species of mice, or it may be merely an expression of the variability of an exceptionally unstable race.

I can see no satisfactory grounds for considering the dancer either abnormal or pathological. It is a well-established race, with certain peculiarities to which it breeds true; and no pathological structural conditions, so far as I have been able to learn, have been discovered.

I have presented in this chapter on differences a program rather than a completed study. To carry out fully the lines of work which have been suggested by my observations and by the presentation of results would occupy a skilled observer many months. I have not as yet succeeded in accomplishing this, but my failure is not due to lack of interest or of effort.



In a general way those peculiarities of behavior which suggested the name dancing mouse are inherited. Generation after generation of the mice run in circles, whirl, and move the head restlessly and jerkily from side to side. But these forms of behavior vary greatly. Some individuals whirl infrequently and sporadically; others whirl frequently and persistently, at certain hours of the day. Some are unable to climb a vertical surface; others do so readily. Some respond to sounds; others give no indications of ability to hear. 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. On the basis of this observation, the animals have been classified as right, left, or mixed whirlers. Does the dancer transmit to its offspring the tendency to whirl in a definite manner?

Records of the direction of whirling of one hundred individuals have been obtained. For twenty of these mice the determination was made by counting the number of complete turns in five-minute intervals at six different hours of the day. For the remaining eighty individuals the direction was discovered by observation of the activity of the animals for a brief interval at five different times. Naturally, the former results are the more exact; in fact, they alone have any considerable quantitative value. But for the problem under consideration all of the determinations are sufficiently accurate to be satisfactory.

The distribution of the individuals which were examined as to direction of whirling is as follows.


Males 19 19 12 50 Females 12 23 15 50

The frequency of occurrence of left whirlers among the females is unexpectedly high. Is this to be accounted for in terms of inheritance? In my search for an answer to this question I followed the whirling tendency from generation to generation in two lines of descent. These two groups of mice have already been referred to as the 200 line and the 400 line. The former were descended from Nos. 200 and 205, and the latter from Nos. 152 and 151. Individuals which resulted from the crossing of these lines will be referred to hereafter as of mixed descent. There were some striking differences in the behavior of the mice of the two lines of descent. As a rule the individuals of the 200 line climbed more readily, were more active, danced less vigorously, whirled less rapidly and less persistently, and were in several other respects much more like common mice than were the individuals of the 400 line. It is also to be noted (see Table 5) that few of the litters of the 200 line exhibited auditory reactions, whereas almost all of the litters of the 400 line which were tested gave unmistakable evidence of sensitiveness to certain sounds. These differences at once suggest the importance of an examination of the whirling tendency of each line of descent.

The results for the several generations of each line which I had opportunity to examine are unexpectedly decisive so far as the question in point is concerned.



First generation No. 200, ? No. 205, ? Second generation No. 210, Mixed whirler No. 215, Left whirler Third generation No. 220, Mixed whirler No. 225, Mixed whirler Fourth generation No. 230, Right whirler No. 235, Mixed whirler Fifth generation No. 240, Right whirler No. 245, Left whirler



First generation No. 152, Left whirler No. 151, Left whirler Second generation No. 410, Left whirler No. 415, Right whirler Third generation No. 420, Left whirler No. 425, Left whirler

One line of descent exhibited no pronounced whirling tendency; the other exhibited a strong tendency to whirl to the left. Are these statements true for the group of one hundred individuals whose distribution among the three classes of whirlers has been given? In order to obtain an answer to this question I have reclassified these individuals according to descent and direction of whirling.



Males 7 6 8 21 Females 5 8 8 21 12 14 16 42



Males 4 9 1 14 Females 6 9 4 19 10 18 5 33


9 10 6 25

Three interesting facts are indicated by these results: first, the inheritance of a tendency to whirl to the left in the 400 line of descent; second, the lack of any definite whirling tendency in the 200 line; and third, the occurrence of right and left whirlers with equal frequency as a result of the crossing of these two lines of descent.

It is quite possible, and I am inclined to consider it probable, that the pure dancer regularly inherits a tendency to whirl to the left, and that this is obscured in the case of the 200 line by the influences of a cross with another variety of mouse. It is to be noted that the individuals of the 200 line were predominantly mixed whirlers, and I may add that many of them whirled so seldom that they might more appropriately be classed as circlers.


The white-black discrimination experiments which were made in connection with the study of vision and the modifiability of behavior were so planned that they should furnish evidence of any possible tendency towards the inheritance of modifications in behavior. The problem may be stated thus. If a dancing mouse be thoroughly trained to avoid black, by being subjected to a disagreeable experience every time it enters a black box, will it transmit to its offspring a tendency to avoid black?

Systematic training experiments were carried on with individuals of both the 200 and 400 lines of descent. For each of these lines a male and a female were trained at the age of four weeks to discriminate between the white and the black electric-boxes and to choose the former. After they had been thoroughly trained these individuals were mated, and in course of time a male and female, chosen at random from their first litter, were similarly trained. All the individuals were trained in the same way and under as nearly the same conditions as could be maintained, and accurate records were kept of the behavior of each animal and of the number of errors of choice which it made in series after series of tests. What do these records indicate concerning the influence of individually acquired forms of behavior upon the behavior of the race?



Number of Errors in Daily Series of Ten Tests



No. 210 No. 220 No. 230 No. 240 No. 215 No. 225 No. 235 No. 245

A 6 5 6 7 8 4 4 7 B 6 8 8 8 8 7 6 5

1 6 7 6 5 7 6 5 4 2 4 3 1 5 5 6 4 5 3 3 1 4 5 3 4 4 3 4 5 0 3 4 2 1 3 1 5 3 0 4 2 1 3 3 0 6 2 1 4 2 2 1 1 1 7 1 0 3 1 1 1 2 0 8 0 0 1 0 0 0 2 3 9 0 0 0 1 1 0 0 0 10 0 0 1 0 2 1 1 11 0 0 0 3 0 0 12 0 0 0 0 0 13 0 0 0 0 14 0

I have records for four generations in the 200 line and for three generations in the 400 line.[1] As the results are practically the same for each, I shall present the detailed records for the former group alone. In Table 53 are to be found the number of errors made in successive series of ten tests each by the various individuals of the 200 line which were trained in this experiment. The most careful examination fails to reveal any indication of the inheritance of a tendency to avoid the black box. No. 240, in fact, chose the black box more frequently in the preference series than did No. 210, and he required thirty more tests for the establishment of a perfect habit than did No. 210. Apparently descent from individuals which had thoroughly learned to avoid the black box gives the dancer no advantage in the formation of a white-black discrimination habit. There is absolutely no evidence of the inheritance of this particular individually acquired form of behavior in the dancer.

[Footnote 1: This experiment was interrupted by the death of the animals of both lines of descent.]


Abnormal dancers. Acquired forms of behavior. Act, useless, repeated. Activity, periods of. Affirmation, choice by. Age, peculiarities; maximum age; and intelligence. Albino cat; dog. Alexander and Kreidl, young dancer; behavior; tracks of mice; behavior in cyclostat; behavior of white mouse and dancer; structure of ear; deafness. Allen, G. M., drawing of dancer; heredity in mice. Alleys, width of, in labyrinths. Amyl acetate for photometry. Anatomy of dancer. Animals, education of. Appuun whistles. Audition. See Hearing. Averages, dangers in.

Baginsky, B., model of ear of dancer. Bateson, W., breeding experiments. Behavior, of dancer; inheritance of; when blinded; equilibration; dizziness; structural bases of; of young; changes in; useless acts; under experimental conditions; in indiscriminable conditions; value of sight; in labyrinth experiments; modifiability of; history of; explanations of; individual differences in. Blinded dancers, behavior of. Blue-orange tests; blue-red tests; blue-green tests; blue-green blindness. Bradley papers. Brain, structure of. Breeding of dancers. Brehm, A. E., "Tierleben". Brightness vision; preference; check experiments; relation to color vision.

Cages for dancers. Candle meter. Candle power. Cardboards, for tests of vision; positions of. Care of dancer. Castle, W. E., drawing of mouse; cages. Cat, albino; training of. Cerebellum of dancer. Characters, acquired. Check experiments. China, dancers of. Choice, exhibition of; by affirmation; by negation; by comparison; methods of. Circling, a form of dance. Circus course mice. Cleghorn, A. G. Climbing of dancer. Cochlea, functions of. Color blindness. Color discrimination apparatus. Colored glasses. Colored papers. Color patterns of dancers. Color vision, problem; methods of testing; tests with colored papers, tests with ray filters, orange-blue tests, yellow-red tests, light blue-orange tests, dark blue-red tests, green-light blue tests, violet-red tests, green-blue tests, green-red tests, blue-green tests, blue-red tests, structure of the retina, conclusions, of different animals, Comparative pedagogy, Comparison, choice by, Cones, lacking in eye of dancer, Corti, organ of, in dancer, Cotton mouse, Curves, of habit formation, irregularities of, of labyrinth habit, of discrimination habit, of learning and re-learning, of plasticity, Cyclostat, behavior of dancer in, Cyon, E. de, dancer pathological, behavior, behavior of blinded dancers, varieties of dancer, space perception, individual differences, anatomy of dancer, hearing of dancer, pain cries.

Dancers, occurrence among common mice, varieties of, hybrid, Dancing, forms of dance movement, whirling, circling, figure-eights, manege movements, solo dance, centre dance, direction of, periods of, amount of, causes of, sex differences in, individual differences in, Darbishire, A. D., breeding experiments with dancers, Deafness of dancer, causes of, Descent, lines of, Development of young dancer, Differences, individual, sex, Direction of movement, choice by, Direction of whirling, Discrimination, visual, box, of brightness, white-black and black-white, of grays, habits, by odor, by form, method, habit defined, Diseases of dancer, Dizziness, visual, rotational, Docility, Dog, albino, training of, fear of electric shock.

Ear, structure of, structural types, model of, of rabbit, functions of, movements of, Educability of dancer, Education, human, methods of, of vision, Efficiency of training, Electric-box for visual tests, Electric-labyrinth for habit experiments, Electric-shock as punishment for mistakes, Epidemic among dancers, Equilibration in dancer, Error curves, form of, Error records versus time records, Errors, in labyrinths, nature of, types of, value of, number of, Even numbers to designate males, Excitability of dancer, Experience, value of, influence of, Eyes, of dancer opening of retina of

Fear, in dancer Females, designated by odd numbers dancing of voice of See Sex Fighting of dancers Figure eight dance Filters for obtaining colored light Food of dancer Form discrimination Frog, reactions of repetition of act by Functions of eye

Galton whistle Gestation, period of, in dancer Gray papers Green blue tests Green-red tests Grouping for averages Guaita, G von, breeding experiments with dancers

Haacke, W, description of dancer, origin of dancer breeding experiments Habit, of dancing, discrimination, useless labyrinth, duration of, reacquisition of, relations of, Habit formation, and the senses, versus habit performance, in the dancer and in the common mouse, curves of, speed of Habituation to sounds Hacker, dancing shrews Hair, appearance of Hamilton, G V, experiments with dog Hatai, S, the dancer Head, shape of, in dancer Hearing, in dancer in young in adult methods of testing, in frog Hefner unit of light Heredity See Inheritance Hering, E, colored papers History, of dancer of acts Hunger as motive in experiments Hybrid dancers

Imitation in dancer Index of modifiability Individuality Inheritance Inhibition of an act Initiative of dancer Insight of dancer Intelligence, measures of, comparisons Interrupted circuit for experimental use Irregular labyrinths

Janssen-Hoffman spectroscope Japan, dancers in Judgment in dancer

Kammerer, P, dancing wood mice, Kishi, K, dancer in Japan origin of race, equilibration, blinded dancer, structure of ear, wax in ears, tests of hearing Koenig tuning forks, steel bars Kreidl, A See Alexander

Labyrinth, forms of, labyrinth A, errors in, tests, labyrinth B, tests, labyrinth C, labyrinth D, a standard labyrinth, regular and irregular labyrinths Labyrinth errors and individual tendencies Labyrinth habits, Labyrinth method, Labyrinth path, formula, method of recording, Ladder climbing tests, Landois, H, account of dancer, Lathrop, A, dancers, Learning, process, methods of in dancer, by being put through act, by imitation, by rote, rapidity of, permanency of, learning and relearning, curves of, Left whirlers, Life span of dancer, Light, reflected, transmitted, unit of measurement, control of, Litter, size of, in dancer, Lummer-Brodhun photometer.

Males, dancing of, fighting and killing young, designation of, voice of, See Sex Manege movements, Mark, E L, cages, Maze See Labyrinth Measurements, of light, of rapidity of habit formation, of intelligence, of efficiency of training, Memory, defined, for ladder climbing, tests of, measurements of, span of, for brightness, for color, Method, of studying dance, for testing hearing, indirect, for testing vision, motives, for brightness vision, for color vision, of shifting filters, of testing form discrimination, of testing Weber's law, development of methods, of choice, food box, labyrinth, of recording errors, of training problem method, labyrinth method, discrimination method, of recording labyrinth path, qualitative versus quantitative, of studying senses, values of methods, of measuring intelligence, quantitative, comparisons of, Milne-Edwards, origin of dancer, Mitsukun, K, the dancer in Japan, Mixed whirlers, Modifiability, of behavior, of useless acts, index of, Motives, for activity, for choice, avoidance of discomfort, in labyrinths, desire to escape, to get food, to avoid pain, Motor, tendencies, ability, capacity Movements, of ears, Mus musculus L, Mus spiciosus L, Mus sylvaticus L.

Nankin nesumi, name for dancer, Negation, choice by, Nendel, R, gray papers, Nerve, eighth, Nervous system, Nest materials, Noises, effects of, Numbers, odd for females, even for males, reference, See Bibliographic List.

Odors, discrimination by, Old Fancier's description of dancer, Olfactory sense See Smell Orange-blue tests, Orientation of dancer, Origin of dancer; by selectional breeding; by inheritance of an acquired character; by mutation; by pathological changes; by natural selection.

Panse, R., structure of ear; explanation of deafness. Papers, Nendel's grays; Bradley's colored; Hering's colored. Parker, G. H. Path in labyrinth, record of. Pathological condition of dancer. Pedagogy, comparative. Perception, of brightness; of color; of movement; of form. Peru, dancers in. Petromyzon, semicircular canals of. Photometer, Lummer-Brodhun. Plasticity of dancer; curves of. Position choice by, of cardboards. Preference for brightness, tests of. Preliminary tests. Probable error. Problems, of structure; of method. Punishment versus reward. Putting-through, training by.

Qualitative methods. Quantitative methods.

Rabbit, ear of. Rawitz, B., behavior of dancer; structure of ear; deafness of dancer; hearing in young. Ray filters. Reactions, to sounds; to disagreeable stimuli; valueless. Reasoning, implicit. Reconstruction method. Records, of markings of dancers; of time; of errors; of path. Red, stimulating value of; vision. Reference numbers to literature. See Literature on Dancer. Reflected light. Refrangibility and vision of dancer. Regular labyrinth. Re-learning, relation to learning; curves of. Reliability of averages. Repetition of useless acts. Rest-interval. Restlessness, of dancer; cause of. Retina of dancer. Retzius, ear of rabbit. Reward, for performance of act; versus punishment. Right whirlers; behavior in labyrinth; occurrence of; inheritance of tendency. Rods of retina. Rotational dizziness. Rubber stamps of labyrinths.

Saint-Loup, R. Schlumberger, C.; wood carving with dancers. Selenka, ear of rabbit. Semicircular canals. Sense organs. Senses, and habit formation; differences in. Sensitiveness Sex, recognition of, designation of, peculiarities Shellac to coat cards Shrews, dancing Sight, role of, See Vision, Brightness Vision, and Color Vision Smell sense of, in labyrinth habits Sniffing by dancer Solutions as ray filters Sorex vulgaris L Sound, reactions to Space perception Spectroscope Spectrum, stimulating value of Standard, candle, light, labyrinth Stine, W M, photometrical measurements Strength of dancer Structure, of brain, of ear, of eye Swinhoe, mice in China

Temperament of animal Temperature sense Tests, visual, number of, per day, Threshold of discrimination Time records Touch, and labyrinth habits Training conditions of, Weber's law, methods of, and retraining, in labyrinths, efficiency of, two test, ten-test, twenty-test, continuous, relation to methods, spread of Transmitted light.

Variability of dancer, Variable light. Varieties of dancer Violet red tests Vision, brightness vision, color vision, training of, importance of, conclusions concerning Visual dizziness Voice of dancer

Watson, J B, habit formation Waugh, K, color vision apparatus, retina of mouse Wax, plugs of, in ear of mouse Weber's law, tests of, apparatus Weldon, W F R, breeding experiments, Whirling of dancer

Yellow Red tests Young dancers, killing of, by male, description of, development of, hearing of, intelligence of, size of

Zoth, O, origin of dancer, size of young mice, the senses of dancer, behavior, dancing, equilibration, climbing dancers, individual differences, tests of hearing, vision


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