A man’s action is capricious if he is biassed by the present motive
alone, without considering other motives which he would have under other
circumstances. A deliberate man equalises, as it were, his actions by
forming rules of conduct. An arbitrary man does not recognise rules or
laws, made either by himself or by others.
LITERARY CORRESPONDENCE
I.
RECENT EVOLUTIONARY STUDIES IN GERMANY.
Since Darwin’s death, his theory, which in Germany more than elsewhere
received its development, has but few decisive steps in advance to
point to, even though the circle of its adherents has been enlarged and
though in many respects and in special directions it has been rendered
more complete and placed upon a firmer foundation. It is a gratifying
fact, that most, if not all, of the recent discoveries in zoology,
palæontology, and particularly in developmental history, are easily and
completely reconcilable with the principles originally established; so
that the views which we have reached on this subject have lost more and
more the characters of a purely hypothetical fabric.
But the accurate investigations of developmental history have
unquestionably furnished the most important material in proof of the
theory in question, and the principles established in this department,
in the main the results of the labors of German investigators (E. von
Baer, Fritz Müller, E. Haeckel), have been verified in a truly surprising
manner.
It is true that Darwin himself in no way undervalued the importance
of the results of the studies in question, but how little the facts
known at the time of the enunciation of his theory of natural selection
sufficed, is most clearly proved by the fact that E. von Baer and Louis
Agassiz, who at that time were perhaps the greatest authorities in
embryology, assumed a hostile attitude towards the new Darwinian theory.
Agassiz’s combination of the points of agreement of palæontology and
embryology, his explanation of extinct forms as “prophetic types,” proved
a veritable hindrance to the perception of the truth, and Carl Vogt, who
was his co-worker at that time, appears to have been the last to set
up any opposition to the “fundamental biogenetic principle,” that the
development of the individual repeats in an abbreviated form the history
of his race. Vogt, formerly the champion of advanced views, appears
to-day as the leader of the small band of the opposition.
If we compare the recently published fourth edition of Haeckel’s
_Anthropogeny_, 1891, and the eighth edition of his _History of
Creation_, with the early editions, we cannot help remarking, with
considerable astonishment, despite the enormous increase of fresh
material, the fact that little in the old plans and principles of the
work needs correction. Even the bold generalisations, the inference
as to the identity of form of the original beginnings of all of the
middle or higher classes of animals, the “Gastræa Theory” of Haeckel,
at first so violently opposed, the stress laid upon the equivalence of
the blastoderms in the various orders of animals, nay, even many of
the animal genealogies, really only asserted as a working hypothesis,
have stood the test beyond all expectation; although Du Bois-Reymond
insinuated that the pedigrees of the heroes of Homer were more worthy
of credit. To appreciate the complete victory of these ideas one need
but refer to the discourse _On Recapitulation in Embryology_ with which
A. Milnes Marshall opened the meeting of the Biological Section of the
British Natural History Society at Leeds, September, 1890.
The very conspicuous irregularities in the formation of organised bodies,
which formerly were regarded as monstrosities, or as the freaks and
riddles of the formative instinct, the hare-lips, the cleft palates,
cases of microcephaly, etc., or the conspicuous want of symmetry in the
physical structure of the plaice and sole, formerly made use of by Mivart
and Schimper as unassailable counterproofs of Darwin’s doctrines, have
shaped themselves into the most decisive verifications of his theory;
as in fact, generally, a number of the most splendid evidences of the
correctness of the theory have, as the result of exact investigations
in organic evolution, proceeded from the most obstinate of its supposed
difficulties. Thus, for example, as proof that birds are far removed
from the other classes of vertebrates, the circumstance had been cited
that certain parts connected with the visual organs are in them situated
at the side of the brain, instead of on the dorsal surface, as is the
case with the other vertebrates. But a more exact observation has shown
that this variation in formation is a secondary result, since in each
previous period of development these same organs in the young birds
lie, exactly as in the case of the other vertebrates, on the dorsal
surface, and only shortly before leaving the egg do they move downward
to the sides. In many cases where the development of parts preservable
in fossil conditions is under consideration, as for instance portions of
the skeleton, the hard integuments, and the teeth, a direct proof may, by
comparison, be furnished of the truth of the fact of the correspondence
of the embryological formations of living animals with the final and
permanent forms of their extinct representatives, a fact which was indeed
acknowledged by Agassiz and Vogt, but completely misunderstood. We need
only to recall to mind the exact parallelism which Alexander Agassiz and
Neumayer have demonstrated to exist in the case of echinoderms, Huxley,
Marsh, and others in the formation of the wings of birds, the pelvis of
birds, or the hoofs of horses, in order to stamp this view as one that
cannot be refuted.
Nevertheless, those opposed to this view, as Carl Vogt, His, Heufen,
and others, have not abandoned their position as a hopeless one,
and in recent years have relied particularly upon those cases which
Haeckel, and before him, Fritz Müller, characterised as a falsification
(cenogenesis[16]) or a supplementary alteration and abbreviation of the
natural process of development. “Nature is no falsifier,” these opponents
proclaim with emphasis, and everything it does is correct and true, and
“this false heart alone brings untruth and deceit into the true heaven,”
they cry with Wallenstein. People who rely on verbal sophistries merely
betray thereby their want of valid counter-arguments. A _mala fides_
on the part of nature can of course never be the subject of discussion
among reasonable beings, but a deviation in the process of development
of certain varieties from the typical path of the development of the
remaining varieties of the species, is _felt_ as a falsification by
every investigator who has thoroughly studied the regular processes,
for the reason that it has a tendency to _obscure_ the original facts.
Thus, for example, in the embryos of certain vertebrates the æsophagus
is temporarily completely closed, as Balfour has observed in young
sharks, Bles and Marshall in frogs; and this state of affairs may well
be considered as a falsification, since an animate being with a closed
æsophagus is a natural contradiction, which can never have existed and
here happens as a supplementary and temporary process.
As a rule such deviations from the normal course may be classified as
consequences of a prolonged residence of the animal germs in the egg
or in the womb, the result of which is that owing to the presence of
an abundant quantity of nourishing yolk, or through direct connection
with the circulatory system of the mother, they in the early stages of
their development are relieved of the necessity of acquiring nourishment
through their own efforts, and therefore all the contrivances necessary
to that purpose may be dispensed with. For this reason we find the
primitive processes of development, as Professor Sollas has lately shown,
most frequently preserved in marine animals which have never changed nor
abandoned their element in the course of the history of their species,
in the case of which, therefore, no occasion could ever have arisen
for supplementary changes in the process of their development. Much
more frequently do we meet with this change in the case of fresh-water
animals, for often the rapid currents of their elements, for example a
river, will not suffer these to leave the egg in any very helpless larval
condition, and in addition fresh water is subject to other unfavorable
changes, as the drying up of streams. Also the larvæ of carnivorous
animals, which from the very beginning of independent life need more
strength to acquire their means of existence, are so completely developed
in the richly provisioned eggs in which they take their form, that they
emerge therefrom in an almost perfected state of being, as, for example,
young sharks and cephalopods. In this kind of animal life, as well as in
the case of forms which are brought forth alive from the parent, although
they see the light of day much later, comparatively, there takes place
not only a great abbreviation of the first stages of existence in the
entering upon a more direct path of development, but also changes occur
in the form of the original designs because of the limitation of room
due to the presence of yolk in the egg, the reason for which is easy
to perceive. In many other cases the mechanical cause of the change in
development can be directly recognised; for example, in the case of, the
tree-toad of the Antilles (_Hylodes marticinensis_), which, owing to the
absence of pools lasting through the dry season, is obliged of necessity
to remain in the egg during its tadpole stage, that is to say, to skip
this stage, as it were; for which reason the formation of external gills
in its case is entirely omitted.
The explanation of the origin of new organs seemed at first to afford
an insuperable difficulty to the Darwinian theory, since, as Mivart
objected, it was not possible to perceive how natural selection could
be able to effect the formation of new organs unless they executed
corresponding functions from the very beginning. This difficulty,
however, has been completely overcome by the theory of altered
functions (_Functionswechsel_) which was first proposed by Dorhn, and
particularly in recent years by Kleinenberg. According to this theory,
in all these cases we have simply to deal with a gradual change in form
of already existing organs, which, originally being used to perform
one set of functions, are modified so as to perform another. Thus the
later developed organs of mastication and the feelers of insects were
originally organs of locomotion, legs; and these in the still earlier
stages of creeping motion performed appropriate functions as the
crooked appendages of the body-rings. The wings of birds were, in their
progenitors, forelegs; the tongue of air-breathing vertebrates originated
from the fish-bladder, which before that was chiefly an organ of swimming.
The knowledge thus acquired of the natural connection of the processes
of evolution also explains, according to Kleinenberg, why organs which
are at present completely useless, must yet necessarily appear in the
formation of the embryo; for example, the gill-openings in the higher
classes of vertebrates, which have no functions to perform at any stage
of vertebral development, and which furnished Meckel the first intimation
of the fundamental biogenetic law. But as soon as it was explained
that the gill-openings furnished the foundation of the development of
later-appearing organs with actual functions to perform, it was rendered
clear why they should continually recur; namely, because they form the
indispensable links of a chain which extends from the dim past of the
type in question down to the present time.
There is no doubt that profounder researches in evolutionary history will
furnish still more important results: for instance, the more perfect
elucidation of the pedigree of mammals; for in this province even our
domestic animals are not sufficiently investigated. Every new effort in
this direction, for example the recent work of Klever on the evolution
of the teeth of the horse, and other investigations concerning the
formation of special organs, has invariably shown that much in this field
yet remains to be discovered. We have only to recall to mind the recent
investigations relating to the development of the pineal gland, which
in the last decennium have also led to the discovery of a rudimentary
occipital eye, which seems to have actually existed and performed
functions in numerous early representatives of the vertebrates, but
to-day is simply a fact of history, and has given rise to an organ which
Descartes considered as the seat of the soul. We may here also refer to
the recent investigations concerning the earlier developmental stages of
the duckbills, which have completely confirmed what the theory asserted
in advance and required; namely, that they fill the vacancy between the
egg-laying reptiles and the mammalia which bring forth their young alive.
Only a few years ago Carl Vogt vehemently opposed the opinion of
the duckbills being transitional types, and sought to explain their
inferior stage of organisation, which is also evidenced in their low
blood temperature, as the results of a stunting process (degeneration,
so called). They formed a degenerated branch of marsupials, nothing
more. Later, the remarkable yet long anticipated fact was revealed by
Haacke and Caldwell, 1884, that the duckbills are egg-laying mammals,
a character which certainly could not have been acquired through
degeneration, but which simply shows that they are closely related to
extinct reptilian forms. In one other respect, namely, with regard
to their supply of teeth, the process of degeneration must indeed be
admitted. On this point, Poulton and Thomas discovered a few years
ago that in their early stages they really do possess true teeth,
which, however, just as in the case of certain carnivorous cetacea,
later completely disappear, and are replaced by a sort of horny teeth.
This, however, is really not a true degeneration, but rather a special
adaptation, doubtless beneficial to the animal in some way or other;
and with as little reason as we may regard birds as a degenerated
race in comparison with their progenitors, because they have lost
the numerous teeth which these possessed, with just as little reason
can we hold that the duckbills, in their general organisation, have
suffered any retrogression worth mentioning. On the contrary, the
recent investigations of Marsh and Lemoine concerning the mammals of
the Jurassic and Cretaceous periods point more and more distinctly to
the conclusion, that there existed among these mammals a very large
number which possessed the same degree of organisation as the duckbills
of to-day, now represented by only a few species; a supposition which
the adherents of the theory of evolution made twenty-five years ago. I
do not know that the pedigrees of the heroes of Homer have been so well
preserved!
In many other directions, however, speculation of late years in Germany
has considerably digressed from the facts of experience and from all
probability; especially with reference to the questions of propagation,
variation, and heredity. Here, first of all, are to be mentioned the
works of Weismann, _Ueber die Continuität des Keimplasmas_ (1885),
_Die Bedeutung der sexuellen Fortpflanzung für die Selectionstheorie_
(1886), _Der Rückschritt in der Natur_ (1886), _Die Bedeutung der
Richtungskörperchen für die Vererbungstheorie_ (1887), _Die Hypothese der
Vererbung von Verletzungen_ (1889), and _Ueber Amphimixis_ (1891).
If we revert to the beginnings of this movement we shall find that it
is intimately connected with the more exact study of the processes of
fecundation as perfected through the researches of Strassburger, the
Hertwigs, and other investigators. In connection with the ideas of
Nägeli concerning the so-called idioplasm, the notion was reached that
the matter determinative of heredity was contained in the nucleoli, and
that by the union of the paternal and maternal nucleoli the sum-total of
the parental hereditary tendencies is transmitted to the offspring. This
view was to a certain degree verified by the experiments of the brothers
Hertwig in removing the nucleoli of the eggs of the sea-urchin; the
result being that eggs containing the nucleoli alone, furnished, through
artificial impregnation, results resembling the female parent, whereas
eggs from which the nucleoli had been removed, furnished germs completely
corresponding to the traits of the male parent.
Other processes of fecundation, to which we shall soon recur, had since
1876 produced the impression in the minds of a number of naturalists that
the germ-material led an independent life in the bodies of organisms,
that it possessed only an internal development, and required from the
body nothing but nourishment in order to multiply itself, and to develop
its internal powers uninfluenced by the various vicissitudes of the
body. In the year 1876 Gustav Jaeger in Germany, and Francis Galton, a
cousin of Darwin, almost at the same time in England, called attention
to the observation made some time previously, that in certain animals,
particularly in insects, the development of the egg into the young
offspring begins with the withdrawal of a small portion of the germ from
the component substance of the embryo, which remains at first unchanged
and only later multiplies. This observation was generalised and accepted.
At the commencement of every sexual multiplication the germ-substance,
after impregnation, is divided into two parts, according to its future
purpose; an ontogenetic or personal part, out of which the body is built
up, and a phylogenetic or germinal part, which at first is stored up
unused in the individual, but later furnishes new germ-cells. This idea
led Weismann to his view of the continuity of the germ-plasm, which forms
an unbroken line of descent from the first beginnings of the species and
which is simply nourished by the organisms in which it has its temporary
abode. From this germ-plasm spring _secondarily_ the cells that go to
make up the body (soma); but from these soma-cells no new _germ_-cells
can originate, and consequently none of its inherent or adscititious
qualities are capable of transmission. The somatic cells make up the
mortal and perishable forms of life, while the germ-cells alone insure
the further existence and immortality of the race.
It is easy to perceive that these views, if they could be maintained,
would completely transform the Darwinian theory. Since, if the somatic
cells, that is, the body-parts of animals and plants, with all their
adaptations to soil and climate, to definite modes of life, etc., are
to be deprived of every power to transmit hereditary characters, then
the so-called Lamarckian theory, which should really bear the name of
Erasmus Darwin, would be deprived of every foundation which it possesses.
Neither the increase in strength of the members of the body, acquired
by use and practice, nor their weakness created by their non-use could
be inherited; and in just as small a degree could changes caused by
external influences, bodily injuries, sickness, entail consequences which
were inheritable. This being the case, then also all those views would
be untenable which seek to explain the important effects of time as the
result of the accumulation and augmentation of the minute impressions of
the external environment. If the variations which are generated by means
of external influences are not capable of transmission, then the direct
adaptation must commence at the beginning in the case of every following
generation; an accumulation is impossible.
We can observe, however, in every particular case, the complete harmony
in which every living being exists with its surroundings and mode of
life; and observe in closely related species the most various adaptations
to the elements in which they live: climate, food, nay, even to the
particular companions with which they associate; with the result that
many plants have shaped the structure of their flowers to conform to
the physical anatomy of the insect which ordinarily effects their
fertilisation, and that animals assume the figure and form of some
associate who is safe from hostile assaults, or even completely adopt
different modes of life where it is necessary to enter a life-partnership
with a strange animal or plant. But, granting that the most widely
extended capability of adaptation is a thing of daily experience, there
still arises the question how we shall explain this quality, which can
only be brought about by slow degrees, without taking into account the
factor of heredity in the transmission of acquired qualities. The theory
of Weismann attempts this, in that it takes for granted an infinite
variability in the germ-formative materials, and guides the new forms and
variations thus begotten into the really true path, that is, into the
most successful paths, through the process of natural selection (that
is, through the survival of the fittest as regards environment and all
other things). According to this doctrine, external circumstances have
no direct influence whatever upon the variation of species, as Erasmus
Darwin, Lamarck, and the founder of the theory of natural selection and
all his followers up to that time supposed, but we have to have recourse
to a pure theory of natural selection, and call to our aid an, even
now, rather obscure phenomenon, occurring in connection with sexual
impregnation, which has been called “the expulsion of the polar bodies,”
an extrusion of minute qualities of germ-plasm from the germ-cells while
in union. By the processes of crossing, which continually recur, a vast
number of the most manifold hereditary tendencies are united in the
germ-material. Then certain of these are ejected, so that others acquire
supremacy; and in this manner the way is opened for the origination of a
vast number of possible combinations. In this way the path is clear to a
theory of perfect mechanical variability, in which the germ-material has
only to transmit the characters which spontaneously arise in it, and yet
affords an investigator endowed with any imagination the possibility of
understanding the origin of the great variety and final purpose of the
world. It is Frohschammer’s “principle of the imagination as the creator
of the world” translated into comprehensible formulæ. The simplicity
thus reached by the elimination of all direct influences from the
external world, has won the adherency of many investigators following in
Darwin’s steps, particularly in England; but whilst Wallace, Galton, Ray
Lankester, and others have expressed their full assent to it, other and
not less eminent authorities, as Herbert Spencer, Haeckel, Fritz Müller,
and Virchow, have emphatically rejected it.
The reasons in favor of this assumption are, as is indeed the whole view
itself, mainly of a theoretical nature; the arguments of the opposition
are divided into philosophical and experiential propositions. The
philosophical opposition is mainly based on the fact that, from the very
beginning, there is assigned to the germ-material, as it unceasingly
continues its existence, an infinite variety of capacities which the
external world cannot affect, and that all progress and advancement takes
place as the result of the _loss_ of the originally endowed powers and
tendencies. On this theory a family of acrobats or race-horses would
not acquire their powers through the gradual augmentation by practice
of their feats of skill and endurance, but because these powers were
originally resident in them, and every factor incompatible with them
was gradually eliminated. On the other hand, these views approach in a
dangerous degree to the theories of predestination and preformation,
the overthrow of which has been justly regarded as one of the greatest
advances of science.