The Dancing Mouse | Page 8

the
peculiarities of behavior of the parents appeared.
In view of this proof of the occurrence of dancing individuals among
common mice, Saint Loup believes that the race of dancers has resulted
from the inheritance and accentuation of an "accidental" deviation from
the usual mode of behavior. It is scarcely necessary to say that this
opinion would be of far greater weight had he observed, instead of
postulating, the inheritance of the peculiarities of movement which he
has described. It might be objected, to the first of his so-called facts,
that the litter resulted from the mating of mice which possessed dancer
blood. Until the occurrence of dancers among varieties of mice which
are known to be unmixed with true dancers is established, and further,
until the inheritance of this peculiar deviation from the normal is
proved, Saint Loup's account of the origin of the dancing mouse race
must be regarded as an hypothesis.
The occurrence of dancing individuals among common mice has been
recorded by several other observers. Kammerer (20 p. 389) reports that
he found a litter of young wood mice (Mus sylvaticus L.) which
behaved much as do the spotted dancers of China. He also observed,
among a lot of true dancers, a gray individual which, instead of

spinning around after the manner of the race, turned somersaults at
frequent intervals. It is Kammerer's opinion, as a result of these
observations, that the black and white dancers of China and Japan have
been produced by selectional breeding on the basis of this occasional
tendency to move in circles. Among albino mice Rawitz (25 p. 238) has
found individuals which whirled about rapidly in small circles. He
states, however, that they lacked the restlessness of the Chinese dancers.
Some shrews (Sorex vulgaris L.) which exhibited whirling movements
and in certain other respects resembled the dancing mouse were studied
for a time by Professor Häcker of Freiburg in Baden, according to a
report by von Guaita (17 p. 317, footnote). Doctor G. M. Allen of
Cambridge has reported to me that he noticed among a large number of
mice kept by him for the investigation of problems of heredity[1]
individuals which ran in circles; and Miss Abbie Lathrop of Granby,
Massachusetts, who has raised thousands of mice for the market, has
written me of the appearance of an individual, in a race which she feels
confident possessed no dancer blood, which whirled and ran about in
small circles much as do the true dancers.
[Footnote 1: Allen, G.M. "The Heredity of Coat Color in Mice." Proc.
Amer. Academy, Vol. 40, 59-163, 1904.]
Although it is possible that some of these cases of the unexpected
appearance of individuals with certain of the dancer's peculiarities of
behavior may have been due to the presence of dancer blood in the
parents, it is not at all probable that this is true of all of them. We may,
therefore, accept the statement that dancing individuals now and then
appear in various races of mice. They are usually spoken of as freaks,
and, because of their inability to thrive under the conditions of life of
the race in which they happen to appear, they soon perish.
Another and a strikingly different notion of the origin of the race of
dancers from those already mentioned is that of Cyon (11 p. 443) who
argues that it is not a natural variety of mouse, as one might at first
suppose it to be, but instead a pathological variation. The pathological
nature of the animals is indicated, he points out, by the exceptionally
high degree of variability of certain portions of the body. According to

this view the dancing is due to certain pathological structural conditions
which are inherited. Cyon's belief raises the interesting question, are the
mice normal or abnormal, healthy or pathological? That the question
cannot be answered with certainty off-hand will be apparent after we
have considered the facts of structure and function which this volume
presents.
Everything organic sooner or later is accounted for, in some one's mind,
by the action of natural selection. The dancing mouse is no exception,
for Landois (22 p. 62) thinks that it is the product of natural selection
and heredity, favored, possibly, by selectional breeding in China. He
further maintains that the Chinese dancer is a variety of _Mus musculus
L._ in which certain peculiarities of behavior appear because of
bilateral defects in the brain. This author is not alone in his belief that
the brain of the dancer is defective, but so far as I have been able to
discover he is the only scientist who has had the temerity to appeal to
natural selection as an explanation of the origin of the race.
Milne-Edwards, as quoted by Schlumberger (29 p. 63), is of the
opinion that the