Professor Fleischmann, zoologist in Erlangen, recently published a book
bearing the title, "Die Descendenztheorie," in which he opposes every
theory of Descent. The book is made up of lectures delivered by the
author before general audiences of professional students, hence is
popular in form and of very special apologetic value. Numerous
excellent illustrations aid the reader in understanding the text.
One statement in the Introduction characterizes the decided position
assumed by the author. He says: "After long and careful investigation I
have come to the conclusion that the doctrine of Descent has not been
substantiated. I go even farther and maintain that the discussion of
the question does not belong to the field of the exact sciences of
zoology and botany." At the outset, Fleischmann establishes the fact
that in the animal kingdom there are rigidly separated types, which
cannot be derived from each other, whereas the doctrine of Descent
postulates "one single common model of body-structure" from which all
types have been developed. Cuvier in his day, set up four such types of
essentially different structure; when Darwin's work appeared two more
had been added; R. Hertwig postulates even seven, Boas nine (both
1900); J. Kennel (1893) seventeen, and Fleischmann himself sixteen. In
consequence the doctrine of Descent has become more complicated since
it now embraces sixteen or seventeen different problems, each of which
in turn gives rise to many subordinate problems.
The discussion which the author inaugurates regarding the domain to
which the question of Descent belongs, is very well-timed. He forcibly
and definitely discountenances the method which transfers it to the
domain of religion. The question must be decided by the naturalists
themselves according to the strict inductive method; that is, the
solution must be based on well ascertained facts, without resorting to
conclusions deduced from general principles. "Exact research must show
that living organisms actually have overstepped the bounds defining
their species, and not merely that they conceivably may have done so."
Hence it is absolutely necessary to procure the intermediary forms.
This is the foundation on which Fleischmann builds and against which no
opponent can prevail. Fleischmann first discusses the differences
between the classes of vertebrates; the mammals, birds, reptiles,
amphibians and fish. For if the differences of their bodily structure
could be shown to be one of degree and not radical, it could be
supposed that the lines of demarcation which now delimitate the larger
types might some day vanish. A single illustration suffices for
Fleischmann's purpose, viz., the plan of structure of the limbs of the
different classes of vertebrates. The four higher classes are
characterized by a common underlying plan of limb structure, whilst
fish have one peculiar to themselves. On the other hand it is an
inevitable postulate of the doctrine of Descent that fish are the
original progenitors of all other vertebrates. Hence the five-joint
limbs of the latter must have developed from the fins of fish. This
derivation was actually attempted but without success, as Fleischmann
points out at considerable length. By means of citations taken from the
writings of Darwinian adherents, he illustrates the confusion which
even now reigns among them on this matter. The evolution of the
remaining vertebrates from the fish is therefore a wholly gratuitous
assumption devoid of any foundation in fact.
Fleischmann further discusses the "parade-horse" of the theory of
Descent. It has been the common belief, especially fostered by Haeckel,
that the history of the Descent of our present horse lies before us in
its complete integrity as pictured in the drawings of Marsh. Here
Fleischmann again proves at great length the insufficiency of actually
available materials. Of special importance is his repeated demand that
not only individual parts of the animals but the whole organism as well
should be derived from the earlier forms. If, for instance, it be
possible to arrange horses and their tertiary kindred in an unbroken
line of descent according to the formation of their feet, whilst the
other characteristics (teeth, skull-structure, etc.,) do not admit of
arrangement in a corresponding series, the first line must be
surrendered.
Very similar to this is the case of the "family history of birds,"
which as all know, has been traced back to reptiles. It is in this
matter that the famous Archaeopteryx plays an important part.
Unfortunately, however, grave difficulties are again encountered in
this connection. This primitive form is a real bird according to
Zittel; and according to the same investigator as also according to
Marsh, Dames, Vetter, Parker, Tuerbringen, Parlow and Mehnert, it is
inadmissible to connect birds with a definite class of reptiles.
Haeckel finds his way out of the difficulty by supplying hypothetical
forms which no one has ever seen, but which his imagination has
admirably depicted as transitional forms. In so doing, however, he
abandons the inductive method of natural science.
It is impossible for us to treat at such length all the remaining
sections of this important book. We may mention in passing that
Fleischmann examines the "roots of the mammal stock," and enters upon a
detailed discussion of "the origin of lung-breathing vertebrates," the
"real phylo-genetic problem of the mollusks," and "the origin of the
echinodermata." It is evident that he boldly takes up the most
important problems connected with the theory of Descent, and does not
confine himself to a one-sided discussion of individual points. As he
did not fear to examine thoroughly the famous, and as it hitherto
appeared, invulnerable, "parade-horse," so neither does he hesitate to
demolish the other reputed proof for the doctrine of Descent, e.g., the
fresh-water snail of Steinheim, the remains of which Hilzendorf and
Neumayr examined and were said to have arranged in lines of descent
that "would actually stagger one." It is important to call especial
attention to this because the adversaries of the book ignore it. He
next shows up the so-called "fundamental principle of biogenesis"
according to which organisms are supposed to repeat during their
individual development the forms of their progenitors (enunciated by
Fritz Mueller and Haeckel). Fleischmann points out the exceptions which
Haeckel attributes to "Cenogenesis," (that is to falsification) and
shows the disagreement among contemporary naturalists regarding this
fundamental principle. Even Haeckel's friend and pupil, O. Hertwig
sounds the retreat.
The 15th chapter deals with the "Collapse of Haeckel's Doctrine," which
is revealed in the fact that "the practical possibility of ascertaining
anything regarding the primitive history of the animal kingdom is
completely exhausted and the hope of so doing forever frustrated."
"Instead of scientists having been able from year to year to produce an
increasing abundance of proof for the correctness of the doctrine of
Descent, the lack of proofs and the impossibility of procuring evidence
is to-day notorious." In the last chapter Fleischmann finally attempts
to prove on logical principles the untenableness of the evolutionary
idea.
He starts from the fact that philosophers use the word development to
designate a definite sequence of ideas, i.e., in a logical order.
"Metamorphosis, says Hegel, belongs to the Idea as such since its
variation alone is development. Rational speculation must get rid of
such nebulous concepts as the evolution of the more highly developed
animal organisms from the less developed, etc."
Naturalists use the word in a different sense. Instead of a sequence of
grades of being they posit a sequence of transformations; instead of a
logical sequence of ideas they posit a transforming and progressive
development. Zoology constructs a system of specific and generic
concepts, "an animal kingdom with logical relations." Our concepts are
derived from natural objects, but in reality do not perfectly
correspond to them. The phylogenetic school commits the capital mistake
of presenting a transformation which can be realized only in logical
concepts, as an actually occurring process, and of confounding an
abstract operation with concrete fact. "The logical transformation of
the concept ape into the concept man is no genealogical process." The
mathematician may logically 'develop' the concept of a circle from that
of a polygon, but it by no means follows that the circle is
phylo-genetically derived from the polygon.
Because the concept of species is variable, the species themselves,
according to Darwin, should be subject to a continual flux; whereas the
real cause of the variability which he observed lies in the discrepancy
between objective facts and their logical tabulation, in the narrowness
of our concepts and in the lack of adequate means of expression. He
thus makes natural objects responsible for our logical limitations.
With regard to organisms the Descent-school confounded the purely
logical signification of the word "related" with that of blood or
family affinity. But surely when they speak of the relation of forms in
the crystal systems, they do not refer to genetic connection. To-day
this interchange of concepts is so general that one needs to exercise
great care if one would avoid it.
The theory which postulates the blood-relationship of individuals of
the same species may be correct, but it is utterly incapable of proof,
and the same is true in a greater degree when there is question of
individuals of the same class but of different species. Since a direct
proof is impossible, an attempt was made to construct an indirect proof
by a comparison of bodily-organs. But in so doing the Descent
theorizers had to relinquish scientific analysis altogether.
In conclusion Fleischmann states that he does not mean to discard every
hypothesis of Descent. He simply gives warning against an
over-estimation of the theory. In opposition to those who esteem it as
the highest achievement of science, he looks upon it as a necessary
evil. Its proper sphere is the laboratory of the man of science, and
not the thronging market-place.
"The Descent hypothesis will meet the same fate (be cast aside), since
its incompatibility with facts of ordinary observation is manifesting
itself. At the time of its appearance in a new form, forty years ago,
it exercised a beneficial influence on scientific progress and induced
a great number of capable minds to devote themselves to the study of
anatomical, palaeontological and evolutionary problems. Meanwhile,
however, viewed in the light of a constantly increasing wealth of
actual materials, the hypothesis has become antiquated and the labors
of its industrious advocates makes it obvious to unbiased critics, that
it is time to relegate it ad acta."
* * * * * * *
My own views agree with those of Fleischmann as presented above, except
in regard to his last chapter. I must, of course, admit that his
criticism has discredited the doctrine of Descent as a scientifically
established theory. Hence, as I have always asserted, it must be
excluded from the realm of exact science. No doubt people will come
gradually to see that the theory involves a creed and therefore belongs
to the domain of cosmic philosophy. All this I readily admit.
Not so, however, as regards the concept of "development." It seems to
me to be incorrect to regard this as a logical concept only, even with
reference to organisms. True, the whole zoological system is in reality
nothing more than a logical abstraction. And in view of this fact one
must be on one's guard against confusing a logical transformation of
concepts with a genealogical development.
We must, however, not forget that we possess the wonderful analogy of
ontogeny (individual development) and above all, the fact of mutation
and of metagenesis. And even if we wish to avoid the error of Haeckel
and others who find a necessary connection between ontogeny and
phylogeny, nevertheless the analogy will still entitle us to picture to
ourselves the development of the whole range of living organisms. Such
a representation will, of course, have only a subjective value.
No doubt, it is logically unjustifiable to argue from the variable
concept to the variability of the species. Still there is something
real in plants and animals which corresponds to our specific concepts.
In some cases the corresponding reality may be so well defined that it
is not difficult to form the concept accurately; whereas in other cases
where the task is more difficult, the difficulty must be due to the
object. Under these circumstances we may safely conclude from the lack
of definiteness in our concepts to a certain lack of rigid delimitation
in the organic forms.
This blending of certain forms suggests the idea of transformation, but
does not furnish definite proof of it. Such proof can be had only by
the direct observation of a transformation. And no doubt in certain
cases a transformation may occur. As regards animals, I may call
attention, for instance, to the experiments made with butterflies by
Standfuss, and as regards plants, to the experiments of Haberlandt, of
which I treated in Chapter III. The limits within which these
transformations take place are indeed very narrow as are also the
limits of those indisputable varieties which naturally arise within an
otherwise rigidly defined species. I am aware that the transformation
of one species into another has not yet been effected, but the
above-mentioned attempts at transformation have nevertheless
demonstrated that certain organic forms when subjected to changed
conditions of life, display certain mutations which clearly show that
variability is to be attributed, not, certainly, to the specific
concepts, but to the corresponding reality. This observation and
reflexion, joined with the fact that organisms form a progressive
series from the simple to the more complex, and with the observed
phenomena of individual development, lead me to regard the concept of
Descent as admissible, and in a certain sense, even probable. But I
agree with Fleischmann in saying that this is a mere belief, and that
all attempts to give it a higher scientific value by inductive proof
have signally failed.
My standpoint, moreover, requires me to admit the validity of the
hypothesis of Descent as an heuristic maxim of natural science. I
believe that we shall be justified in the future, as we were forty
years ago, in directing our investigation in the direction of Descent,
and I do not consider such investigation so utterly hopeless as
Fleischmann represents it. However, I entirely concur with him in the
opinion that we are here concerned (and shall be for a long time to
come) with a mere hypothesis which belongs not in the market-place, nor
among the world views of the multitude, but in the study of the man of
science.
Above all it must not be mixed up with religious questions. Whether the
hypothesis will ever emerge from the study of the man of science as a
well-attested law, is still an open question, incapable of immediate
solution.
* * * * * * *
It is of interest for us to inquire what reception Fleischmann's
protest against the theory of Descent has been accorded by his
associates.
Fleischmann was formerly an advocate of the theory of Descent. He was a
pupil and assistant of Selenka, who was then at Erlangen (died in
Muenster 1902). He had previously written a number of scientific works
from the standpoint of the Descent theory. In the year 1891,
investigations regarding rodents led him to oppose that theory. During
the winter term of 1891-92 he gave evidence of this change in a public
lecture. Not until 1895 was there question of his appointment to the
chair of zoology in Erlangen. In 1898 he published a Manual of Zoology
based on principles radically opposed to the doctrine of Descent. This
manual irritated Haeckel so much that he issued one of his well-known
articles, _Ascending and Descending Zoology_, in which, after his
usual manner, he casts suspicion on Fleischmann of having received his
appointment to the chair at Erlangen by becoming an anti-Darwinian in
accordance with a desire expressed at the diet of Bavaria. I am not
aware that Haeckel has paid any attention to the work of Fleischmann
which we have just reviewed.
By its publication, however, the author disturbed a hornet's nest.
Dispassionate, but still entirely adverse is Professor Plate's review
in the "Biologisches Zentralblatt," while the "Umschau" publishes two
criticisms, one by Professor von Wagner, the other by Dr. Reh, which
for want of sense could not well be equalled. It was the former who
furnished material for our sixth chapter and who there displayed such
utter confusion of thought regarding the inductive method. The same
confusion is apparent in his recent utterance in which he observes that
Fleischmann's whole aim is to accumulate observational data, meanwhile
avoiding speculation as far as possible. His criticism is replete with
bitter personal epithets, e.g., "reactionary," "mental incompetency,"
"dishonest mask of hypercritical exactness," which manifest the
writer's inability to enter upon an objective discussion of the
question.
A still more reprehensible position is assumed by Dr. Reh, who censures
Fleischmann for introducing to the general public the question of
Descent which belongs properly to the forum of science. He claims that
Fleischmann, by so doing, forfeited his right to an unbiased hearing.
Dr. Reh forgets that but a short time ago he had no word of censure for
Haeckel's _Weltraetsel_ which was intended for a far wider circle
of readers. He next appropriates Haeckel's suspicion regarding
Fleischmann which we noticed above, and then adds the entirely untrue
assertion that the first half of Fleischmann's Manual, written before
he took possession of the chair in Erlangen, is written in the spirit
of Darwin, whereas the second half which appeared at a later date is
written in the contrary spirit. He then takes individual points of
Fleischmann's treatise out of their context in order to execute a cheap
and nonsensical criticism of them. Haeckel has evidently been giving
instructions on the best manner of dealing with adversaries. And very
docile disciples they are who imitate his method even to the extent of
defaming and abusing their scientific opponents.
But is not this another plain indication of the decay of Darwinism? Of
course Haeckel recognized at the very beginning of his career that it
was necessary to support the theory by means of personal bitterness,
forgeries and misrepresentations. But if the last surviving advocates
of Darwinism must needs have recourse to the same disreputable means,
to what a low estate, indeed, has it fallen!
Let us hope that these last wild convulsions are really the signs of
approaching dissolution.