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The Dancing Mouse

R >> Robert M. Yerkes >> The Dancing Mouse




[Footnote 1: I have not been able thus far to determine the average length
of the dancer's life. The greatest age to which any of my individuals has
attained is nineteen months.]

To test the same individuals month after month would be the ideal way of
obtaining an answer to our question, but I could devise no satisfactory
way of doing this. The effects of training last so long, as the results of
the previous chapter proved, and the uncertainty of their entire
disappearance is so serious, that the same training process cannot be used
at successive ages. The use of different methods of training is even more
unsatisfactory because it is extremely difficult to make accurate
quantitative comparison of their results. It was these considerations that
forced me to attempt to discover the relation of docility to age by
carrying out the same experiments with groups of individuals of different
ages.

As my plan involved the execution of precisely the same set of tests with
at least seventy individuals whose age, history, and past experience were
accurately known, and of which some had to be kept for nineteen months
before they could be trained, the amount of labor and the risk of mishap
which it entailed were great. To make possible the completion of the
investigation within two years, I accumulated healthy individuals for
several months without training any of them. In March, 1907, I had
succeeded in completing the tests for the age of one month, and I had on
hand for the remaining tests almost a hundred individuals, whose ages
ranged from a few days to eighteen months. Had everything gone well, the
work would have been finished within six months. Suddenly, and without
discoverable external cause, my mice began to die of an intestinal
trouble, and despite all my efforts to check the disease by changing food
supply and environment, all except a single pair died within a few weeks.
Thus ended a number of experiments whose final results I had expected to
be able to present in this volume. However, the work which I have done is
still of value, for the single pair of survivors have made possible the
continuance of my tests with other individuals of the same line of descent
as those which perished, and I have to regret only the loss of time and
labor.

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.



TABLE 52

PLASTICITY (RELATION or MODIFIABILITY TO AGE)

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



SERIES MALES FEMALES

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



[Illustration: FIGURE 33.--Plasticity curves. In the left margin are given
the indices of modifiability (the number of tests necessary for the
establishment of a perfect habit). Below the base line the age of the
individuals is given in months. Curve for males, --•--•--•--; curve for
females, - - - -; curve for both males and females,----. When these three
plasticity curves are completed, they will represent the indices of
modifiability as determined for ten individuals at the age of 1 month, and
similarly for the same number of individuals at each of the ages, 4, 7,
10, 13, 16, and 19 months.]

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 preëminent 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.




CHAPTER XVIII

THE INHERITANCE OF FORMS OF BEHAVIOR

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.



RIGHT WHIRLERS LEFT WHIRLERS MIXED WHIRLERS TOTAL

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.



INDIVIDUALS OF THE 200 LINE

MALES FEMALES

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

INDIVIDUALS OF THE 400 LINE

MALES FEMALES

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.



INDIVIDUALS OF THE 200 LINE

RIGHT WHIRLERS LEFT WHIRLERS MIXED WHIRLERS TOTAL

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




INDIVIDUALS OF THE 400 LINE

RIGHT WHIRLERS LEFT WHIRLERS MIXED WHIRLERS TOTAL

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

INDIVIDUALS OF MIXED DESCENT

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 INHERITANCE OF INDIVIDUALLY ACQUIRED FORMS OF
BEHAVIOR

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?



TABLE 53

THE INHERITANCE OF THE HABIT OF WHITE-BLACK DISCRIMINATION

Number of Errors in Daily Series of Ten Tests


MALES FEMALES

SERIES FIRST SECOND THIRD FOURTH FIRST SECOND THIRD FOURTH
GENERA- GENERA- GENERA- GENERA- GENERA- GENERA- GENERA- GENERA-
TION TION TION TION TION TION TION TION

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.]





INDEX


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.

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