(1887) Meeting of the Association of German Naturalists, at Wiesbaden.
These cats had inherited their taillessness, or rather their
rudimentary tails, from the mother cat, which ‘was said’ to have lost
her tail by the wheel of a cart having passed over it. Not only did the
owner of the cats, Dr. Zacharias, consider them as a proof of the
transmission of mutilations, but in a recently-published work, entitled
‘On the Origin of Species, based upon the Transmission of acquired
characters’ (‘Ueber die Entstehung der Arten auf Grundlage des
Vererbens erworbener Eigenschaften’), the author, Prof. Eimer, speaks
of these cats in the preface as a ‘valuable’ instance of the
transmission of mutilations: these examples therefore form part of the
foundation upon which the author builds up his theoretical views.
Certainly, the want of tails in young cats, of which the mother had
lost its tail by an accident, would have been well worth consideration,
but unfortunately there is no trustworthy record as to how the mother
cat became tailless. Without absolute certainty upon this point the
evidence becomes utterly worthless; and Dr. Zacharias has acted very
wisely in afterwards admitting that this is the case, for inherent
taillessness has been known in cats for a long time. The tailless race
of the Isle of Man is mentioned in the first edition of ‘The Origin of
Species’; of course I am referring to Darwin’s work, and not to the
above-mentioned book of the same name, by Prof. Eimer. As to the first
origin of the tailless Manx breed we know no more than about the origin
of that remarkable race of cats with supernumerary toes, which E. B.
Poulton has recently described from Oxford, and has traced through
several generations[298]. These are innate monstrosities which have
arisen from unknown changes in the germ. Similar monstrosities have
been known for a long time, and no one has ever doubted that they can
be transmitted.
It would be equally justifiable to derive the cats with extra toes from
an ancestor of which the toes had been trodden upon, as to derive the
tailless cats of the Isle of Man from an ancestor of which the tail had
been cut off by a cart passing over it, and thus to regard the
existence of the race as a proof of the transmission of mutilations.
But even if it were certain that the tail of the mother cat had been
mutilated, such a fact would not necessarily prove that the rudimentary
tails of the offspring were due to transmission from the mother: they
might have been transmitted from the unknown father. This is probably
not the case with Dr. Zacharias’ cat, for tailless kittens occurred in
several families produced by the same mother; but in other cases the
possibility of the possession of innate taillessness by the father must
be taken into account. The following case is, in this respect, very
instructive.
Last summer, my friend, Prof. Schottelius, of Freiburg, brought me a
kitten with an innate rudimentary tail, which he had accidentally
discovered as one of a family of kittens at Waldkirch, a small town in
the southern part of the Black Forest. The mother of the kitten
possessed a perfectly normal tail; the father could not be identified.
A closer investigation resulted in the following rather unexpected
discovery. For some years past, tailless kittens have frequently
appeared in the families of many different mother cats at Waldkirch,
and this fact is explained in the following manner. A clergyman, who
lived for some time at Waldkirch, had married an English lady who
possessed a tailless male Manx cat. The probability that all the
tailless cats in Waldkirch are more or less distant descendants of that
male cat almost amounts to certainty. Since a male Manx cat has reached
the Black Forest, it might equally well arrive at some other place.
But we will now leave observations such as these, which do not prove
the transmission of a mutilation, because the mutilation itself has not
been established; and we will turn to more serious ‘proofs.’
Let us still consider the tails of domesticated animals. In these
animals a spontaneous and considerable reduction of the tail occurs not
uncommonly, and since the habit of cutting off part of the tail of
young animals prevails in many countries, the coincidence has been
explained as a causal relation, and the question has been raised
whether the disposition towards the spontaneous appearance of
rudimentary tails has not arisen in consequence of the artificial
mutilation practised through many generations. This supposition appears
very plausible at first sight, but the keen scientific criticism of
Döderlein, Richter, and Bonnet, together with careful anatomical
investigations, have shown that, at least in the cases which were
carefully examined, such a causal connection did not exist. It has been
shown that the spontaneous rudimentary tails which occasionally appear
in cats and dogs have an entirely different origin from the
transmission of artificial mutilation. They depend upon an innate
peculiarity of the germ, a peculiarity which is easily and strongly
transmitted. They are monstrosities, like the sixth finger or toe, or,
rather, like the rudimentary fingers and toes, which also occasionally
appear. Bonnet[299] has shown that the rudimentary tails of dogs depend
upon the absence of several vertebrae, together with an abnormal
ossification, and sometimes also with a premature coalescence, of the
vertebrae of the tail.
Bonnet states that in the two first cases examined by him the reduction
occurred at the distal end of the vertebral column in the tail, the
more or less malformed vertebrae being anchylosed. A membranous
appendage extended beyond the end of the reduced caudal vertebrae, as
the so-called ‘soft tail.’ These characters were shown to have been
inherited from the mother and to have undergone progressive development
as regards the number of missing vertebrae and the proportion of
individuals with rudimentary tails.
In a third instance Bonnet found that four to seven of the normal
caudal vertebrae were absent, and that the column in the region of the
tail was characterised by a tendency towards premature anchylosis along
its whole length and not merely in its distal portion. Furthermore the
last three to four vertebrae were distorted and were either placed
transversely to the long axis of the tail, or were so greatly curved
that the tip of the tail was directed forwards.
It is obvious that these changes are not such as we should expect as a
result of the transmission of the mutilation of the tail which is so
commonly practised. If the artificial injury were transmitted we should
not expect that a variable number of the mesial vertebrae would be
absent, but rather those of the tip. There would be no reason why the
existing vertebrae should be degenerate as in the majority of the
caudal vertebrae of the dogs examined by Bonnet.
Entirely similar phenomena have been observed by Döderlein in the
tailless cats which not infrequently occur in Japan. In these cats the
rudimentary vertebrae of the tail were reduced to a short, thin,
inflexible spiral, which formed a knot densely covered with hair on the
posterior part of the animal.
Such a reduction of the tail occurs quite independently of artificial
injury, in individuals of which the parents were not injured: it is
even found in races, such as the dachshund, which, as far as we know,
have never been habitually mutilated.
But the fact is rendered especially interesting because the reduction
of the vertebral column in the region of the tail takes place in very
various degrees. Sometimes only four vertebrae are absent, sometimes as
many as ten. The degree of abnormality in shape and the degree of
coalescence between the vertebrae also differ greatly. Hence Bonnet
rightly concludes that a slow and gradual process of reduction is going
on in these animals, a process which tends, as it were, to shorten the
tail. I intentionally say ‘as it were,’ for of course the statement
must not be taken literally, and we must not conclude that the process
of reduction is a consequence of some hypothetical developmental force
seated in the organism, of which the purpose is to remove the tail. On
the contrary, this instance shows very clearly that the appearance of a
development guided in a certain direction may be produced without the
existence of any motive developmental force.
The disposition of the tail to become rudimentary, in cats and dogs,
may be explained in the simplest way, by the process which I have
formerly called panmixia. The tail is now of hardly any use to these
animals; and neither dog nor cat would perish because they possessed
only an incomplete tail. Hence natural selection does not now exercise
any influence over these parts, and an occasional reduction is no
longer eliminated by the early destruction of its possessor: therefore
such reduction may be transmitted to the offspring.
The race of tailless foxes which, according to Settegast, existed
during the present century on the hunting-grounds of Prince Wilhelm zu
Solms-Braunfels, very soon disappeared; while cats and dogs with
rudimentary tails have been preserved in many cases. Such results are
to be expected, because in these domesticated animals the absence of
the tail did not cause any inferiority in the struggle for existence.
But these facts appear to me to be remarkable in another direction. I
previously mentioned the tailless race of Manx cats. Tradition does not
tell us how it happened that the descendants of the first tailless cat
in the Isle of Man were able to increase and spread in such a manner as
to form the dominant race in the island. But we can easily imagine how
it happened, when we learn that tailless cats are especially
prized[300] in Japan, because people think that they are better
mousers. Every one in Japan wishes to possess a tailless cat, and
people even cut off the tails of normal cats when they cannot obtain
those with congenital rudimentary tails, because they believe that cats
become better mousers in consequence of taillessness. In Waldkirch the
same account of the superiority of tailless cats is curiously enough
also found. We thus see how a slight but striking variation may at once
cause an energetic process of artificial selection, which helps this
variation to predominance: a hint for us to be careful in passing
judgment upon sexual selection, for the latter also works upon such
functionally indifferent but striking variations. In the case of the
cats, man has favoured a particular variation, because the novelty
rather than the beauty of the character surprised and attracted him. He
has attached an imaginary value to the new character, and by artificial
selection has helped it to predominate over the normal form. I see no
reason why the same process should not take place in animals by the
operation of sexual selection.
But now, after this little digression, let us return to the
transmission of mutilations.
We have seen that the rudimentary tails of cats and dogs, as far as
they can be submitted to scientific investigation, do not depend upon
the transmission of artificial mutilation, but upon the spontaneous
appearance of degeneration in the vertebral column of the tail. The
opinion may, however, be still held that the customary artificial
mutilation of the tail, in many races of dogs and cats, has at least
produced a number of rudimentary tails, although, perhaps, not all of
them. It might be maintained that the fact of the spontaneous
appearance of rudimentary tails does not disprove the supposition that
the character may also depend upon the transmission of artificial
mutilation.
Obviously, such a question can only be decided by experiment: not, of
course, experiments upon dogs and cats, as Bonnet rightly remarks, but
experiments upon animals the tails of which are not already in a
process of reduction. Bonnet proposes that the question should be
investigated in white rats or mice, in which the length of the tail is
very uniform, and the occurrence of rudimentary tails is unknown.
Before this suggestion was made, I had already attacked the problem
experimentally. Such a course might, perhaps, have been more natural to
those who maintain the transmission of mutilations, to which I am
opposed. Although I undertook the experiments expecting to obtain
purely negative results, I thought that the latter would not be
entirely valueless; and since the numerous supporters of the
transmission of acquired characters do not seem to be willing to test
their opinion experimentally, I have undertaken the not very large
amount of trouble which is necessary in order to conduct such an
experimental test.
The experiments were conducted upon white mice, and were begun in
October of last year (1887), with seven females and five males. On
October 17 all their tails were cut off, and on November 16 the two
first families were born. Inasmuch as the period of pregnancy is only
22-24 days, these first offspring began to develope at a time when both
parents were without tails. These two families were together eighteen
in number, and every individual possessed a perfectly normal tail, with
a length of 11-12 mm. These young mice, like all those born at later
periods, were removed from the cage, and either killed and preserved,
or made use of for the continuance of the breeding experiments. In the
first cage, containing the twelve mice of the first generation, 333
young were born in fourteen months, viz. until January 16, 1889, and no
one of these had a rudimentary tail or even a tail but slightly shorter
than that of the offspring of unmutilated parents.
It might be urged that the effects of mutilation do not exercise any
influence until after several generations. I therefore removed fifteen
young, born on December 2, 1887, to a second cage, just after they were
able to see, and were covered with hair; their tails were cut off.
These mice produced 237 young from December 2, 1887 to January 16,
1889, every one of which possessed a normal tail.
In the same manner fourteen of the offspring of this second generation
were put in cage No. 3 on May 1, 1888, and their tails were also cut
off. Among their young, 152 in number, which had been produced by
January 16, there was not a single one with an abnormal tail. Precisely
the same result occurred in the fourth generation, which were bred in a
fourth cage and treated in exactly the same manner. This generation
produced 138 young with normal tails from April 23 to January 16.
The experiment was not concluded with the fourth generation; thirteen
mice of the fifth generation were again isolated and their tails were
amputated; by January 16, 1889 they had produced 41 young.
Thus 901 young were produced by five generations of artificially
mutilated parents, and yet there was not a single example of a
rudimentary tail or of any other abnormity in this organ. Exact
measurement proved that there was not even a slight diminution in
length. The tail of a newly-born mouse varies from 10.5 to 12 mm. in
length, and not one of the offspring possessed a tail shorter than 10.5
mm. Furthermore there was no difference in this respect between the
young of the earlier and later generations.
What do these experiments prove? Do they disprove once for all the
opinion that mutilations cannot be transmitted? Certainly not, when
taken alone. If this conclusion were drawn from these experiments alone
and without considering other facts, it might be rightly objected that
the number of generations had been far too small. It might be urged
that it was probable that the hereditary effects of mutilation would
only appear after a greater number of generations had elapsed. They
might not appear by the fifth generation, but perhaps by the sixth,
tenth, twentieth, or hundredth generation.
We cannot say much against this objection, for there are actual
phenomena of variation which must depend upon such a gradual and at
first imperceptible change in the germ-plasm, a change which does not
become visible in the descendants until after the lapse of generations.
The wild pansy does not change at once when planted in garden soil: at
first it remains apparently unchanged, but sooner or later in the
course of generations variations, chiefly in the colour and size of the
flowers, begin to appear: these are propagated by seed and are
therefore the consequence of variations in the germ. The fact that such
variations _never_ occur in the first generation proves that they must
be prepared for by a gradual transformation of the germ-plasm.
It is therefore possible to imagine that the modifying effects of
external influences upon the germ-plasm may be gradual and may increase
in the course of generations, so that visible changes in the body
(_soma_) are not produced until the effects have reached a certain
intensity.
Thus no conclusive theoretical objections can be brought forward
against the supposition that the hereditary transmission of mutilations
requires (e. g.) 1000 generations before it can become visible. We
cannot estimate _a priori_ the strength of the influences which are
capable of changing the germ-plasm, and experience alone can teach us
the number of generations through which they must act before visible
effects are produced.
If therefore mutilations really act upon the germ-plasm as the causes
of variation, the possibility or even probability of the ultimate
appearance of hereditary effects could not be denied.
Hence the experiments on mice, when taken alone, do not constitute a
complete disproof of such a supposition: they would have to be
continued to infinity before we could maintain with certainty that
hereditary transmission cannot take place. But it must be remembered
that all the so-called proofs which have hitherto been brought forward
in favour of the transmission of mutilations assert the transmission of
a single mutilation which at once became visible in the following
generation. Furthermore the mutilation was only inflicted upon one of
the parents, not upon both, as in my experiments with mice. Hence,
contrasted with these experiments, all such ‘proofs’ collapse; they
must all depend upon error.
It is for this reason important to consider those cases of habitual
mutilation which have been continually repeated for numerous
generations of men, and have not produced any hereditary consequences.
With regard to the habitually amputated tails of cats and dogs I have
already shown that there is only an apparently hereditary effect.
Furthermore, the mutilations of certain parts of the human body, as
practised by different nations from times immemorial, have, in not a
single instance, led to the malformation or reduction of the parts in
question. Such hereditary effects have been produced neither by
circumcision[301], nor the removal of the front teeth, nor the boring
of holes in the lips or nose, nor the extraordinary artificial crushing
and crippling of the feet of Chinese women. No child among any of the
nations referred to possesses the slightest trace of these mutilations
when born: they have to be acquired anew in every generation.
Similar cases can be proved to occur among animals. Professor Kühn of
Halle pointed out to me that, for practical reasons, the tail in a
certain race of sheep has been cut off, during the last hundred years,
but that according to Nathusius, a sheep of this race without a tail or
with only a rudimentary tail has never been born. This is all the more
important because there are other races of sheep in which the shortness
of the tail is a distinguishing peculiarity. Thus the nature of the
sheep’s tail does not imply that it cannot disappear.
A very good instance is mentioned by Settegast, although perhaps with
another object in view. The various species of crows possess stiff
bristle-like feathers round the opening of the nostrils and the base of
the beak: these are absent only in the rook. The latter, however,
possesses them when young, but soon after it has left the nest they are
lost and never reappear. The rook digs deep into the earth in searching
for food, and in this way the feathers at the base of the beak are
rubbed off and can never grow again because of the constant digging.
Nevertheless this peculiarity, which has been acquired again and again
from times immemorial, has never led to the appearance of a newly
hatched individual with a bare face.
Thus there is no reason for the assumption that such a result would
occur in the case of the mice even if the experiments had been
continued through hundreds or thousands of generations. The supposition
of the accumulative effect of mutilation is entirely visionary, and
cannot be supported except by the fact that accumulative
transformations of the germ-plasm occur; but of course this fact does
not imply that mutilations belong to those influences which are capable
of changing the germ-plasm. All the ascertained facts point to the
conclusion that they have not this effect. The transmission is all the
more improbable because of the striking form of the mutilation in all
cases which are relied upon as evidence. The only objection which can
be raised is to suppose that the absence of the tail is less easily
transmitted than other mutilations, or that mice possess smaller
hereditary powers than other animals. But there is not the slightest
evidence in favour of either of these suggestions; the supporters of
the Lamarckian principle have, on the contrary, always pointed to the
transmission of mutilated tails as one of their principal lines of
evidence.
The opinion has often been expressed that such transmission need not
occur in every case, but may happen now and then under quite
exceptional conditions with which we are unacquainted: for this reason
it might be urged that all negative experiments and every refutation of
the ‘proofs’ of the transmission of mutilations are not conclusive.
Only recently, a clever young zoologist said in reference to Kant’s
statements upon the subject, that perhaps the most decided opponent of
the transmission of mutilations would not venture nowadays to maintain
his view with such certainty, ‘for it must be admitted that the
transmission of acquired characters may take place at any rate as a
rare exception.’ Similar opinions are often expressed, especially in
conversation, and yet they can mean nothing except that the
transmission of acquired characters has been proved; for if such
transmission can take place at all, it exists, and it does not make the
least difference theoretically whether it occurs in rare cases or more
frequently. Sometimes heredity has been called capricious, and in a
certain sense this is true. Heredity appears to be capricious because
we cannot penetrate into its depths: we cannot predict whether any
peculiar character in the father will reappear in the child, and still
less whether it will reappear in the first, second, or one of the later
children: we cannot predict whether a child will possess the nose of
his father or mother or one of the grandparents. But this certainly
does not imply that the results are due to chance: no one has the right
to doubt that everything is brought about by the operation of certain
laws, and that, with the fertilization of the egg, the shape of the
nose of the future child has been determined. The co-operation of the
two tendencies of development contained in the two conjugating
germ-cells produces of necessity a certain form of nose. The observed
facts enable us to know something of the laws under which such events
take place. Thus, for instance, among a large number of children of the
same parents some will always have the form of the nose of the mother
or of the mother’s family; others will have the nose of the father’s
family, and so on.