THE RELATION OF LAMARCK AND DARWIN TO MORPHOLOGY.
It is a remarkable fact that morphology took but a very little part in
the formation of evolution-theory. When one remembers what powerful
arguments for evolution can be drawn from such facts as the unity of
plan and composition and the law of parallelism, one is astonished to
find that it was not the morphologists at all who founded the theory of
evolution.
It is true that the noticeable resemblances of animals to one another,
the possibility of arranging them in a system, the vague perception of
an all-pervading plan of structure, did suggest to many minds the
thought that systematic affinities might be due to blood-relationship.
Thus Leibniz considered that the cat tribe might possibly be descended
from a common ancestor,[333] and another great philosopher, Immanuel Kant,
was led by his perception of the unity of type to suggest as possible
the derivation of the whole organic realm from one parent form, or even
ultimately from inorganic matter. In the course of his masterly
discussion of mechanism and teleology,[334] he writes, "The agreement of
so many genera of animals in a certain common schema, which appears to
be fundamental not only in the structure of their bones, but also in the
disposition of their remaining parts--so that with an admirable
simplicity of original outline, a great variety of species has been
produced by the shortening of one member and the lengthening of another,
the involution of this part and the evolution of that--allows a ray of
hope, however faint, to penetrate into our minds, that here something
may be accomplished by the aid of the principle of the mechanism of
Nature (without which there can be no natural science in general). This
analogy of forms, which with all their differences seem to have been
produced according to a common original type, strengthens our suspicions
of an actual relationship between them in their production from a common
parent, through the gradual approximation of one animal-genus to
another--from those in which the principle of purposes seems to be best
authenticated, _i.e._, from man down to the polype, and again from this
down to mosses and lichens, and finally to the lowest stage of Nature
noticeable by us, viz., to crude matter."[335]
So, too, Buffon's evolutionism was suggested by his study of the
structural affinities of animals, and Erasmus Darwin in his _Zoonomia_
(1794) brought forward as one of the strongest proofs of evolution, "the
essential unity of plan in all warm-blooded animals."[336]
But, as a matter of historical fact, no morphologist, not even Geoffroy,
deduced from the facts of his science any comprehensive theory of
evolution. The pre-Darwinian morphologists were comparatively little
influenced by the evolution-theories current in their day, and it was in
the anatomist Cuvier and the embryologist von Baer that the early
evolutionists found their most uncompromising opponents.
Speaking generally, and excepting for the moment the theory of Lamarck,
we may say that the evolution-theories of the 18th and 19th centuries
arose in connection with the transcendental notion of the _Echelle des
etres_, or scale of perfection. This notion, which plays so great a part
in the philosophy of Leibniz, was very generally accepted about the
middle of the 18th century, and received complete and even exaggerated
expression from Bonnet and Robinet. Buffon also was influenced by it.
Towards the beginning of the 19th century the idea was taken up eagerly
by the transcendental school and by them given, in their theories of the
"one animal," a more morphological turn. Their recapitulation theory was
part and parcel of the same general idea.
One understands how easily the notion of evolution could arise in minds
filled with the thought of the ideal progression of the whole organic
kingdom towards its crown and microcosm, man. Their theory of
recapitulation led them to conceive evolution as the developmental
history of the one great organism.[337] Many of them wavered between the
conception of evolution as an ideal process, as a _Vorstellungsart_, and
the conception of it as an historical process. Bonnet, Oken, and the
majority of the transcendentalists seem to have chosen the former
alternative; Robinet, Treviranus, Tiedemann, Meckel, and a few others
held evolution to be a real process.
We have already in previous chapters[338] briefly noticed the relation of
one or two of the transcendental evolution-theories to morphology, and
there is little more to be said about them here. They had as good as no
influence upon morphological theory, nor indeed upon biology in
general.[339] It is different with the theory of Lamarck, which, although
it had little influence upon biological thought during and for long
after the lifetime of its author, is still at the present day a living
and developing doctrine.
Lamarck's affinity with the transcendentalists was in many ways a close
one, but he differed essentially in being before all a systematist. Nor
is the direct influence of the German transcendentalists traceable in
his work--his spiritual ancestors are the men of his own race, the
materialists Condillac and Cabanis, and Buffon, whose friend he was. The
idea of a gradation of all animals from the lowest to the highest was
always present in Lamarck's mind, and links him up, perhaps through
Buffon, with the school of Bonnet. The idea of the _Echelle des etres_
had for him much less a morphological orientation than it had even for
the transcendentalists, for he was lacking almost completely in the
sense for morphology. Lamarck's scientific, as distinguished from his
speculative work, was exclusively systematic, and it was systematics of
a very high order. He introduced many reforms into the general
classification of animals. He was the first clearly to separate
Crustacea (1799), and a little later (1800) Arachnids, from insects. He
reduced to a certain orderliness the neglected tribes of the
Invertebrates, and wrote what was for long the standard work on their
systematics--the _Histoire naturelle des Animaux sans Vertebres_
(1816-22). His speculative work on biology is contained in three
publications, the small book entitled _Considerations sur l'organisation
des corps vivants_ (1802), the larger work of 1809, the _Philosophie
zoologique_, and the introductory matter to his _Animaux sans Vertebres_
(vol. i., 1816).
It is no easy matter to give in short compass an account of Lamarck's
biological philosophy. He is an obscure writer, and often
self-contradictory.
In the first part of the _Philosophie zoologique_ Lamarck is largely
pre-occupied with the problem of whether species are really distinct, or
do not rather grade insensibly into one another. As a systematist of
vast experience Lamarck knew how difficult it is in practice to
distinguish species from varieties. "The more," he writes, "we collect
the productions of Nature, the richer our collections become, the more
do we see almost all the gaps filled up and the lines of separation
effaced. We find ourselves reduced to an arbitrary determination, which
sometimes leads us to seize upon the slightest differences of varieties,
and form from them the distinctive character of what we call a species,
and at other times leads us to consider as a variety of a certain
species individuals a little bit different, which others regard as
forming a separate species."[340]
For Lamarck, as for Darwin later, the chief problem was not the
evolution and differentiation of types of structure, but the mode of
origin of species.
Lamarck is at great pains to show how arbitrary are our determinations
of species, and how artificial the classificatory groups which we
distinguish in Nature. Strictly speaking, there are in Nature only
individuals, "... this is certain, that among her products Nature has in
reality formed neither classes, nor orders, nor families, nor genera,
nor constant species, but only individuals which succeed one another and
resemble those that produced them. Now, these individuals belong to
infinitely diversified races, which shade into one another under all the
forms and in all the degrees of organisation, and each of which
maintains itself without change, so long as no cause of change acts upon
it" (p. 41).
But there is a natural order in the animal kingdom, a progression from
the simpler to the more complex organisations, a natural _Echelle des
etres_.
This order is shown by the relation to one another of the large
classificatory groups, for they can be arranged in series from the
simplest to the most complex, somewhat as follows:--
1. Infusoria.
2. Polyps.
3. Radiates.
4. Worms.
5. Insects.
6. Arachnids.
7. Crustacea.
8. Annelids.
9. Cirripedes.
10. Molluscs.
11. Fishes.
12. Reptiles.
13. Birds.
14. Mammals.
But the order of Nature is essentially continuous, and the limits of
even the best defined of these classes are in reality artificial--"if
the order of Nature were perfectly known in a kingdom, the classes which
we should be forced to establish in it would always constitute entirely
artificial sections" (p. 45).
In the same way the lesser classificatory groups represent smaller
sections of the one unique order of Nature. Note that Lamarck's
_Echelle_ is in no way a morphological one, and was not intended to be
such. It is a scale of increasing physiological differentiation, and the
stages of it are marked by the acquirement of this or that new organ
(_cf._ Oken). "Observation of their state convinces one that in order to
produce them successively Nature has proceeded gradually from the
simpler to the more complex. Now Nature, having had in mind the
realisation of a plan of organisation which would permit of the greatest
perfecting (that of the Vertebrates), a plan very different from those
which she has been obliged to form as a preliminary to reaching it, one
understands that, among the multitude of animals, one must necessarily
come across not a single system of organisation which has become
progressively perfected, but diverse very distinct systems, each of
which has come into existence at the moment when each primary organ
first put in its appearance" (p. 171).
For Lamarck this order of Nature was not merely ideal--Nature had
actually formed the classes successively, proceeding from the simpler to
the more complex; she had brought about this evolution by transforming
the primitive species of animals, raising them to higher degrees of
organisation, and modifying them in relation to the environment in which
they found themselves.
Lamarck's theory of evolution is worked out in great detail in his
_Philosophie zoologique_, but the exposition is diffuse and
disconnected; it is better in giving an account of it to follow the more
concise, mature and general exposition which he gives in the
Introduction to his _Histoire naturelle des Animaux sans Vertebres_.[341]
Near the beginning of the Introduction Lamarck gives us in a few short
"Fundamental Principles" the main lines of his general philosophy. He is
a confirmed materialist. Every fact and phenomenon is essentially
physical and owes its existence or production entirely to material
bodies or to relations between them. All change and all movement is in
the last resort due to mechanical causes. Every fact or phenomenon
observed in a living body is at once a physical fact or phenomenon and a
product of organisation (p. 19). Life, thought and sensation are not
properties of matter, but result from particular material combinations.
His thorough-going materialism is most clearly shown in its relation to
living things in the first three of the "Zoological Principles and
Axioms," which are developed further on in the book.
These are as follows:--"1. No kind or particle of matter can have in
itself the power of moving, living, feeling, thinking, nor of having
ideas; and if, outside of man, we observe bodies endowed with all or one
of these faculties, we ought to consider these faculties as physical
phenomena which Nature has been able to produce, not by employing some
particular kind of matter which itself possesses one or other of these
faculties, but by the order and state of things which she has
constituted in each organisation and in each particular system of
organs.
"2. Every animal faculty, of whatever nature it may be, is an organic
phenomenon, and results from a system of organs or an organ-apparatus
which gives rise to it and upon which it is necessarily dependent.
"3. The more highly a faculty is developed the more complex is the
system of organs which produces it, and the higher the general
organisation; the more difficult also does it become to grasp its
mechanism. But the faculty is none the less a phenomenon of
organisation, and for that reason purely physical" (p. 104).
According to these "axioms" function is a direct and mechanical effect
of structure.
The curious thing is that in spite of his avowed materialism, Lamarck's
conception of life and evolution is profoundly psychological, and from
the conflict of his materialism and his vitalism (of which he was
himself hardly conscious), arise most of the obscurities and the
irreductible self-contradiction of his theory.
Lamarck divided animals (psychologically!) into three great
groups--apathetic or insensitive animals, animals endowed with
sensation, and intelligent animals. The first group, which comprise all
the lower Invertebrates, are distinguished from other animals by the
fact that their actions are directly and mechanically due to the
excitations of the environment; they have no principle of reaction to
external influences, but passively prolong into action the excitations
they receive from without. They are _irritable_ merely. The second group
are distinguished from the first by their possessing, in addition to
irritability, a power which Lamarck calls the _sentiment interieur_. He
has some difficulty in defining exactly what he means by it:--"I have no
term to express this internal power possessed not only by intelligent
animals but also by those that are endowed merely with the faculty of
sensation; it is a power which, when set in action by the feeling of a
need, causes the individual to act at once, _i.e._, in the very moment
of the sensation it experiences; and if the individual is of those that
are endowed with intelligence it nevertheless acts in such a case
entirely without premeditation and before any mental operation has
brought its _will_ into play" (p. 24).
It is the power we call instinct in animals (p. 25), and it implies
neither consciousness nor will. It acts by transforming external into
internal excitations.
To this second group of animals, possessing the _sentiment interieur_,
belong the higher Invertebrates, notably insects and molluscs. Only
animals possessed of a more or less centralised nervous system can
manifest this _sentiment_, or principle of (unconscious) reaction to
external stimuli.
The higher animals, or the four Vertebrate classes, form the group of
"intelligent animals." In virtue of their more complex organisation they
possess in addition to the _sentiment interieur_ the faculties of
intelligence and will.
Now, broadly put, Lamarck's theory of evolution is that new organs are
formed in direct reaction to needs (_besoins_) experienced by the
_sentiment interieur_. The _sentiment interieur_ is therefore the cause
not only of instinctive action but also of all morphogenetic processes.
Will and intelligence (which are confined to a relatively small number
of animals) have little or nothing to do directly with evolution.
To understand the working-out of Lamarck's evolution-theory we must
revert to his conception of the _Echelle des etres_. What he wrote in
the _Philosophie zoologique_ is here repeated in the work of 1816 with
little modification.
There is a real progression from the simpler to the more complex
organisations; Nature has gradually complicated her creatures by giving
them new organs and therefore new faculties.
It is interesting to note that Lamarck expressly refers to Bonnet (p.
110), but refuses to accept his view of an _Echelle_ extending down into
the inorganic. Like Bonnet, however, and like the German
transcendentalists, Lamarck makes man the goal of evolution (p. 116). He
makes it quite clear that his _Echelle_ is a functional one, for he
links Vertebrates to molluscs even while expressly admitting that they
are not connected by any structural intermediates (p. 123). He does not
fall into the error of the transcendentalists and assume that
Vertebrates and Invertebrates alike are formed upon one common plan of
structure.
The progression of organisation shown by the animal kingdom has not been
altogether regular and uninterrupted:--"The progression in complexity of
organisation shows here and there, in the general animal series,
anomalies induced by the influence of environment and by the influence
of the habits contracted" (_Phil. zool._, i., p. 145).
There are thus really two causes at work to produce the variety of
organisation as it appears to us, one which tends to produce a regular
increase in complexity, and one which disturbs and diversifies this
regular advance.
The first cause Lamarck calls the vital power (_pouvoir de la vie_); the
other may be called the influence of circumstance (_Anim. s. Vert._, p.
134). To the latter cause are due the lacunae, the blind alleys, and the
complications which the otherwise simple scale of perfection shows.
To explain both these aspects of evolution Lamarck propounded in his
volume of 1816 four laws, which read as follows:--
"_First Law_.--Life, by its own forces, tends continually to increase
the volume of every body possessing it, and to extend the dimensions of
its parts, up to a limit which it brings about itself.
"_Second Law_.--The production of a new organ in an animal body results
from the arisal and continuance of a new need, and from the new movement
which this need brings into being and sustains.
"_Third Law_.--The degree of development of organs and their force of
action are always proportionate to the use made of these organs.
"_Fourth Law_.--All that has been acquired, imprinted or changed in the
organisation of the individual during the course of its life is
preserved by generation and transmitted to the new individuals that
descend from the individual so modified" (pp. 151-2).
It is mainly but not entirely by reason of the first of these laws that
organisation tends to progress, and mainly by reason of the second and
third that difference of environment brings about diversity of
organisation. In virtue of the fourth law the acquirements of the
individual become the property of the race.
Lamarck's exposition of his first law, that life tends by its own powers
to enlarge and extend its bodily instrument, is vague and difficult to
understand. He has already explained some pages back how the first
organisms arose by spontaneous generation in the form of minute
gelatinous utricles (_cf._ Oken). He conceives that it is in the
movements of the fluids proper to the organism that the power resides to
enlarge and extend the body. Nutrition alone is not sufficient to bring
about extension; a special force is required, acting from within
outwards (p. 153). In the most primitive organisms the movements of the
vital fluids are weak and slow, but in the course of evolution they
gradually accelerate, and, becoming more rapid, trace out canals in the
delicate tissue which contains them, and finally form organs.
Subtle fluids play a great part in Lamarck's biology: they take the
place of the soul or entelechy which the vitalists would postulate to
explain organic happenings. Lamarck seems in this to follow certain of
the old materialists, who conceived the soul to be formed of a matter
more subtle than the ordinary.[342]
In his second law Lamarck's essentially vitalistic attitude comes out
very clearly, for it states that a psychological moment enters into all
new production of form, that the ultimate cause of the development of
new form is the need felt by the organism. This need is of course not a
conscious one, it is a need perceived by the _sentiment interieur_.
In the large group of apathetic or insensitive animals, which do not
possess this faculty, needs cannot be experienced; accordingly new
organs are here formed directly and mechanically, by the movements of
the vital fluids set in action by excitations from without--the
evolution, like the behaviour, of these animals is due to the direct and
physical action of the environment. "But this is not the case with the
more highly organised animals which possess _feeling_. They experience
needs, and each need felt, acting upon their 'inner feeling,'
immediately directs the fluids and the forces to the part of the body
where action can satisfy the need. Now, if there exists at this point an
organ capable of performing the required action, it is quickly
stimulated to act; and if the organ does not exist and the need is
pressing and sustained, bit by bit the organ is produced and developed
in proportion to the continuity and the energy of its use" (p. 155).
In intelligent animals the _sentiment interieur_ may be moved by thought
or will.
As an example of the way in which the law works Lamarck takes the
hypothetical case of a gastropod mollusc, which as it creeps along
experiences dimly the need to feel the objects in front of it. It makes
an effort (unconscious, be it noted) to touch these objects with the
anterior portions of its head, and sends forward continually to these
parts a great volume of nervous and other fluids. From these efforts and
the repeated afflux of fluids there must result a development of the
nerves supplying these parts. And as, along with the nervous fluids,
nutritive juices constantly flow to the parts, there must result the
formation of two or four tentacles in the places to which these fluids
are directed. A curious mixture of mechanistic "explanations" and
vitalistic hypothesis!
In his third law, that use and disuse are powerful to modify organs,
Lamarck is upon more solid ground, and can point to many instances of
the visible effect of these factors of change. It is of course rather
closely bound up with his second law and may even be regarded as an
extension of it.
The law has reference to one of the most powerful means employed by
Nature to diversify species, a means which comes into play whenever the
environment changes. The cause of the great diversity shown by animal
species is indeed ultimately to be sought in the environment. As the
imperfect and earliest forms developed they spread over the earth and
invaded the utmost corners of it:--"One can imagine what an enormous
variety of habitats, stations, climates, available foods, environing
media, etc., animals and plants have had to endure, as the existing
species were forced to change their place of abode. And although these
changes have taken place with extreme slowness ... their reality,
necessitated by various causes, has none the less induced the species
affected by them slowly to change their manner of life and their
habitual actions. Through the effects of the second and third of the
laws cited above, these induced activity-changes must have brought into
being new organs, and must have been able to develop them further if
more frequent use was made of them; they must in the same way have been
capable of bringing about the degeneration and finally the complete
disappearance of existing organs which had become useless" (p. 161).
On the other hand, if the environment does not change, species remain
constant.
It is to be noted that change in environment is rather the occasion than
the cause of modification; the environment induces the organism to
change its habitual way of life; it sets up new needs, to satisfy which
the organism must modify its structure. It is the organism that takes
the active part in all this, the action of the environment is indirect.
Of Lamarck's fourth law, which asserts the transmission of acquired
characters, little need here be said in the way of exposition. Upon the
truth of it depends of course Lamarck's whole theory. He himself never
dreamed that anyone would ever dispute it.
Lamarck sums up as follows:--"By the four laws which I have just
enunciated all the facts of organisation seem to me to be easily
explained; the progression in the complexity of organisation of animals,
and in their faculties, seems to me easy to conceive; so, too, the means
which Nature has employed to diversify animals, and bring them to the
state in which we now see them, become easily determinable" (p. 168).
It is never made quite clear, we may note in passing, how far his second
and third laws tend to bring about an increase in complexity, in
addition to diversifying animals.[343]
"The function creates the organ," this would seem to be the kernel of
Lamarck's doctrine. But how does he reconcile this essentially
vitalistic conception with his strictly materialistic philosophy?
We have seen that irritability, the _sentiment interieur_, and
intelligence itself, are the effects of organisation. We are told
farther on that both the _sentiment_ and intelligence are caused by
nervous fluids. A great part of both the _Philosophie zoologique_ and
the introduction to the _Animaux sans Vertebres_ is given up to the
exposition of a materialistic psychology of animals and man, based
entirely upon this hypothesis of nervous fluids. Thus habits are due to
the fluids hollowing out definite paths for themselves.
The _sentiment interieur_ acts by directing the movements of the subtle
fluids of the body (which are themselves modifications of the nervous
fluids) upon the parts where a new organ is needed. But if it is itself
only a result of the movement of nervous fluids? Again, how can a need
be "felt" by a nervous fluid? This is an entirely psychological notion
and cannot be applied to a purely material system. Whence arises the
power of the _sentiment interieur_ to canalise the energies of the
organism, so to direct and co-ordinate them that they build up purposive
structures, or effect purposive actions (as in all instinctive
behaviour)? Either the _sentiment interieur_ is a psychological faculty,
or it is nothing.
There is no doubt that, as expressed by Lamarck, the conception conceals
a radical confusion of thought. It is not possible to be a
thorough-going materialist, and at the same time to believe that new
organs are formed in direct response to needs felt by the organism.
Lamarck could never resolve this antinomy, and his speculations were
thrown into confusion by it. To this cause is due the frequent obscurity
of his writings.
Should we be right in laying stress upon the psychological side of
Lamarck's theory, and disregarding the materialistic dress in which,
perhaps under the influence of the materialism current in his youth, he
clothed his essentially vitalistic thought? Everything goes to prove
it--his constant preoccupation with psychological questions, his tacit
assimilation of organ-formation to instinctive behaviour, his constant
insistence on the importance of _besoin_ and _habitude_.
Let us not forget the profundity of his main idea, that, exception made
for the lower forms, the animal is essentially active, that it always
_reacts_ to the external world, is never passively acted upon. Let us
not forget that he pointed out the essentially psychological moment
implied in all processes of individual adaptation. With keen insight he
realised that conscious intelligence counts for little in evolution, and
focussed attention upon the unconscious but obscurely psychical
processes of instinct and morphogenesis.
Not without reason have the later schools of evolutionary thought, who
developed the psychological and vitalistic side of his doctrine, called
themselves Neo-Lamarckians.
We shall say then that Lamarck, in spite of his materialism, was the
founder of the "psychological" theory of evolution.
Lamarck stood curiously aloof and apart from the scientific thought of
his day.[344] He took no interest in the morphological problems that
filled the minds of Cuvier and Geoffroy; he had indeed no feeling at all
for morphology. He did not realise, like Cuvier, the _convenance des
parties_, the marvellous co-ordination of parts to form a whole; he had
little conception of what is really implied in the word "organism." He
was not, like Geoffroy, imbued with a lively sense of the unity of plan
and composition, and of the significance of vestigial organs as
witnesses to that unity. He seems not to have known of the
recapitulation theory, of which he might have made such good use as
powerful evidence for evolution. Even with the German
transcendentalists, with whom in the looseness of his generalisations he
shows some affinity, he seems not to have been specially acquainted.
He was interested more in the problems suggested to him by his daily
work in the museum. He wanted to know why species graded so annoyingly
into one another; he wanted to examine critically his haunting suspicion
that species were really not distinct, and that classification was
purely conventional. The question, too, of the adaptation of species to
their environment, the problem of ecological adaptation, in distinction
to that of functional adaptation which interested Cuvier so greatly,
came vividly before him as he worked through the vast collections of the
museum. He was the first systematist to occupy himself in a
philosophical manner with the problems of general biology. He introduced
new problems and a new way of looking at old. With Lamarck the problem
of species and the problem of ecological adaptation enter into general
biology.
The one point in which he does definitely carry on the thought of his
predecessors is his conception of the animal kingdom as forming a scale
of (functional) perfection. He did not go to the same extreme as Bonnet;
he did not even consider that the animal series was a continuation of
the vegetable series; in his opinion they formed two diverging scales.
He recognised, too, that among animals there was no simple and regular
gradation from the lowest to the highest, but that the orderly
progression was disturbed and diverted by the necessity of adaptation to
different environments. It is interesting to note that in developing
this idea he arrived at a roughly accurate distinction between
homologous and analogous structures. More importance, he thought, was to
be attributed in classifying animals to characters which appeared due to
the "plan of Nature" than to such as were produced by an external
modifying cause (p. 299). But he did not formulate the distinction in
any strictly morphological way.
As his ideas developed he laid less stress upon the simplicity and
continuity of the scale; in his supplementary remarks to the
Introduction of 1816 he admits that the series is really very much
branched, and even that there may be two distinct series among animals
instead of one. His last schema of the course of evolution shows no
little analogy with the genealogical trees of Darwinian speculation. It
is headed "The presumed _Order_ of the formation of Animals, showing two
separate partly-branching series," and it reads as follows:--
I.--_Series of Non-articulated_ II.--_Series of Articulated_
_Animals_. _Animals_.
"
I |-- Infusoria.
n | |
s A | Polyps.
e n | |
n i | ----------------
s m | | |
i a | Ascidians. Radiates. Worms.
t l | | |
i s | | --------------
v . | | | |
e | | | Epizoa.
" |-- | | |
| | |
" |-- | | |
S A | Acephala. Annelids. Insects.
e n | | |
n i | | |
s m | Molluscs. -------------
i a | | |
t l | | Arachnids.
i s | Crustacea.
v . | |
e | |
" |-- Cirripedes.
I
n |--
t A |
e n | Fishes.
l i | Reptiles.
l m | Birds.
i a | Mammals.
g l |
e s |--
n .
t
It is interesting to note that Vertebrates are placed between the two
series, and are now not linked on directly to any Invertebrate group.
Lamarck's theory had little success. There is evidence, however, that
both Meckel and Geoffroy owed a good many of their evolutionary ideas to
Lamarck, and Cuvier paid him at least the compliment of criticising his
theory,[345] not distinguishing it, however, very clearly from the
evolutionary theories of the transcendentalists. But, speaking
generally, Lamarck's theory of evolution exercised very little influence
upon his contemporaries. This was probably due partly to the obscurity
and confusion of his thought, partly to his lack of sympathy with the
biological thought of his day, which was preponderatingly morphological.
It was not that men's minds were not ripe for evolution, for in the
early decades of the 19th century evolution was in the air. There were
few of von Baer's contemporaries who had not read Lamarck;[346] Erasmus
Darwin's _Zoonomia_ ran through three editions, and was translated into
German, French and Italian;[247] German philosophy was full of the idea of
evolution.
There was no unreadiness to accept the derivation of present-day species
from a primordial form--if only some solid evidence for such derivation
were forthcoming. Cuvier and von Baer, as we have seen, combated the
current evolution theories on the ground that the evidence was
insufficient, but von Baer at least had no rooted objection to
evolution. In an essay of 1834, entitled _The Most General Law of Nature
in all Development_,[348] von Baer expressed belief in a limited amount of
evolution. In this paper he did not admit that all animals have
developed from one parent form, and he refused to believe that man has
descended from an ape; but, basing his supposition upon the facts of
variability and upon the evidence of palaeontology, he went so far as to
maintain that many species have evolved from parent stocks. In the
absence of conclusive proofs he did not commit himself to a belief in
any extended or comprehensive process of evolution.
Imbued as he was with the idea of development von Baer saw in evolution
a process essentially of the same nature as the development of the
individual. Evolution, like development, was due to a _Bildungskraft_ or
formative force. The ultimate law of all becoming was that "the history
of Nature is nothing but the history of the ever-advancing victory of
spirit over matter" (p. 71). In a later essay (1835) in the same volume
he says that all natural science is nothing but a long commentary on the
single phrase _Es werde!_. (p. 86).
As we shall see, von Baer adopted in later years the same attitude to
Darwinism as he did to the evolution theories in vogue in his youth.
Although in the twenty or thirty years before the publication of the
_Origin of Species_ (1859) no evolution theory of any importance was
published, and although the great majority of biologists believed in the
constancy of species, there were not wanting some who, like von Baer,
had an open mind on the subject, or even believed in the occurrence of
evolutionary processes of small scope. Isidore Geoffroy St Hilaire, the
son of the great Etienne Geoffroy St Hilaire, seems to have held that
species might be formed from varieties. The law which L. Agassiz thought
he could establish,[349] of the parallelism between palaeontological
succession, systematic rank, and embryological development, tended to
help the progress of evolutionary ideas. J. V. Carus, who afterwards
became a supporter of Darwin, seems already, in 1853, to have inferred
from Agassiz's law the probability of evolution.[350]
But no evolution theory was taken very seriously before 1859, when the
_Origin of Species_ was published.
Like Lamarck, Charles Darwin was, neither by inclination nor by
training, a morphologist. In his youth he was a collector, a sportsman
and a field geologist. His voyage round the world on the _Beagle_
aroused in him keen interest in the problem of species--their variety,
their variation according to place and time, their adaptedness to
environment. The conviction gradually took possession of his mind that
the puzzling facts of geographical range and geological succession which
he observed wherever he went were explicable only on the hypothesis that
species change. He was not satisfied with the theories of evolution that
had been proposed by his grandfather, by Lamarck, and by E. Geoffroy St
Hilaire--he did not indeed understand these theories any too well. He
resolved to work out the problem in his own way, for his own
satisfaction. He tells us all this very clearly in his autobiography.
"During the voyage of the _Beagle_ I had been deeply impressed by
discovering in the Pampean formation great fossil animals covered with
armour like that on the existing armadillos; secondly, by the manner in
which closely allied animals replace one another in proceeding
southwards over the continent; and thirdly, by the South American
character of most of the productions of the Galapagos archipelago, and
more especially by the manner in which they differ slightly on each
island of the group; some of the islands appearing to be very ancient in
a geological sense.
"It was evident that such facts as these, as well as many others, could
only be explained on the supposition that species gradually become
modified; and the subject haunted me. But it was equally evident that
neither the action of the surrounding conditions, nor the will of the
organisms (especially in the case of plants) could account for the
innumerable cases in which organisms of every kind are beautifully
adapted to their habits of life--for instance, a woodpecker or a
tree-frog to climb trees, or a seed for dispersal by hooks or plumes. I
had always been much struck by such adaptations, and until these could
be explained it seemed to me almost useless to endeavour to prove by
indirect evidence that species have been modified."[351]
All Darwin's varied subsequent work revolved round these, for him,
essential problems--How do species change, and how do they become
adapted to their environment? He never ceased to be essentially a field
naturalist, and his theory of natural selection would have been an empty
and abstract thing if his vast knowledge and understanding of the "web
of life" had not given it colour and form. He never lost touch with the
living thing in its living, breathing reality--even plants he rightly
regarded as active things, full of tricks and contrivances for making
their way in the world. No one ever realised more vividly than he the
delicacy and complexity of the adaptations to environment which are the
necessary condition of success in the struggle for existence. Almost his
greatest service to biology was that he made biologists realise as they
never did before the vast importance of environment. He took biology
into the open air, away from the museum and the dissecting-room.
Naturally this attitude was not without its drawbacks. It led him to
take only a lukewarm interest in the problems of morphology. It is true
he used the facts of morphology with great effect as powerful arguments
for evolution, but it was not from such facts that he deduced his theory
to account for evolution. It is questionable indeed whether the theory
of natural selection is properly applicable to the problems of form. It
was invented to account for the evolution of specific differences and of
ecological adaptations; it was not primarily intended as an explanation
of the more wonderful and more mysterious facts of the _convenance des
parties_ and the interaction of structure and function. Perhaps Darwin
did not realise this inner aspect of adaptation quite so vividly as he
did the more superficial adaptation of organisms to their environment.
It was, perhaps, his lack of morphological training and experience that
led him to disregard the problems of form, or at least to realise very
insufficiently their difficulty.
It is in any case very significant that only a small part of his _Origin
of Species_ is devoted to the discussion of morphological
questions--only one chapter out of the fourteen contained in the first
edition.
Though the theory of natural selection took little account of the
problems of form, Darwin's masterly vindication of the theory of
evolution was of immense service to morphology, and Darwin himself was
the first to point out what a great light evolution threw upon all
morphological problems. In a few pages of the _Origin_ he laid the
foundations of evolutionary morphology.
We have here to consider his interpretation of morphological facts and
its relation to the current morphology of his time.
The sketch of his theory, written in 1842,[352] shows a very significant
division into two parts--the first dealing with the positive facts of
variability and the theory of natural selection, the second with the
general evidence for evolution. It is in the second part that the
paragraphs on morphological matters occur. In paragraph 7, on affinities
and classification, Darwin points out that on the theory of evolution
homological relationship would be real relationship, and the natural
system would really be genealogical. In the next paragraph he notes that
evolution would account for the unity of type in the great classes, for
the metamorphosis of organs, and for the close resemblance which early
embryos show to one another. It is of special interest to note that he
definitely rejects the Meckel-Serres theory of recapitulation. "It is
not true," he writes, "that one passes through the form of a lower
group, though no doubt fish more nearly related to foetal state" (p.
42). The greater divergence which adults show seems to him to be due to
the fact that selection acts more on the later than on the embryonic
stages. He realises very clearly how illuminative the theory of
evolution is when applied to the puzzling facts of embryonic
development. "The less differences of foetus--this has obvious meaning
on this view: otherwise how strange that a horse, a man, a bat should at
one time of life have arteries, running in a manner which is only
intelligibly useful in a fish! The natural system being on theory
genealogical, we can at once see why foetus, retaining traces of the
ancestral form, is of the highest value in classification" (p. 45).
Abortive organs, too, gain significance on the evolutionary hypothesis.
"The affinity of different groups, the unity of types of structure, the
representative forms through which foetus passes, the metamorphosis of
organs, the abortion of others, cease to be metaphorical expressions and
become intelligible facts" (p. 50).
In general, organisms can be understood only if we take into account the
cardinal fact that they are historical beings. "We must look at every
complicated mechanism and instinct as the summary of a long history of
useful contrivances much like a work of art" (p. 51).[353]
Already in 1842 Darwin had seized upon the main principles of
evolutionary morphology: the indications then given are elaborated in
the thirteenth chapter of the _Origin of Species_ (1st ed., 1859). A
good part of this chapter is given up to a discussion of the principles
of classification, only a few pages dealing with morphology proper. But,
as Darwin rightly saw, the two things are inseparable.
We note first that there is no hint of the "scale of beings"--Darwin
conceives the genealogical tree as many branched. Animals can be classed
in "groups under groups," and cannot be arranged in one single series.
He discusses first what kind of characters have the greatest
classificatory value. Certain empirical rules have been recognised, more
or less consciously, by systematists--that analogical characters are
less valuable than homological, that characters of great physiological
importance are not always valuable for classificatory purposes, that
rudimentary organs are often very useful, and so on. He finds that as a
general rule "the less any part of the organisation is concerned with
special habits, the more important it becomes for classification" (p.
414), and adduces in support Owen's remark that the generative organs
afford very clear indications of affinities, since they are unlikely to
be modified by special habits. These rules of classification can be
explained "on the view that the natural system is founded on descent
with modification; that the characters which naturalists consider as
showing true affinity ... are those which have been inherited from a
common parent, and, in so far, all true classification is genealogical;
that community of descent is the hidden bond which naturalists have been
unconsciously seeking, and not some unknown plan of creation, or the
enunciation of general propositions, and the mere putting together and
separating objects more or less alike" (p. 420).
In general, then, homological characters are more valuable for
classificatory purposes because they have a longer pedigree than
analogical characters, which represent recent acquirements of the race.
Coming to morphology proper, Darwin takes up the question of the unity
of type, and the homology of parts, for which the unity of type is but a
general expression.
He treats this on the same lines as E. Geoffroy St Hilaire, and Owen,
referring indeed specifically to Geoffroy's law of connections. "What
can be more curious," he asks, "than that the hand of a man, formed for
grasping, that of a mole for digging, the leg of a horse, the paddle of
the porpoise, and the wing of the bat, should all be constructed on the
same pattern, and should include similar bones, in the same relative
positions? Geoffroy St Hilaire has strongly insisted on the high
importance of relative position or connection in homologous parts; they
may differ to almost any extent in form and size, and yet remain
connected together in the same invariable order" (p. 434).
The unity of plan cannot be explained on teleological grounds, as Owen
has admitted in his _Nature of Limbs_, nor is it explicable on the
hypothesis of special creation (p. 435). It can be understood only on
the theory that animals are descended from one another and retain for
innumerable generations the essential organisation of their ancestors.
"The explanation is to a large extent simple on the theory of the
selection of successive slight modifications--each modification being
profitable in some way to the modified form, but often affecting by
correlation other parts of the organisation. In changes of this nature,
there will be little or no tendency to alter the original pattern or to
transpose the parts.... If we suppose that the ancient progenitor, the
archetype as it may be called, of all animals, had its limbs constructed
on the existing general pattern, for whatever purpose they served, we
can at once perceive the plain significance of the homologous
construction of the limbs throughout the whole class" (p. 435).
We may note three important points in this passage--first, the
identification of the archetype with the common progenitor; second, the
view that progressive evolution is essentially adaptive, and dominated
by natural selection; and third, the _petitio principii_ involved in the
assumption that adaptive modification brings inevitably in its train the
necessary correlative changes.
In his section on morphology Darwin shows clearly the influence of Owen,
and through him of the transcendental anatomists. He refers to the
transcendental idea of "metamorphosis," as exemplified in the vertebral
theory of the skull and the theory of the plant appendage, and shows
how, on the hypothesis of descent with modification, "metamorphosis" may
now be interpreted literally, and no longer figuratively merely (p.
439).
Very great interest attaches to Darwin's treatment of development, for
post-Darwinian morphology was based to a very large extent on the
presumed relation between the development of the individual and the
evolution of the race. Just as he kept clear of the notion of the scale
of beings, so he avoided the snare of the Meckel-Serres theory of
recapitulation, according to which the embryo of the highest animal,
man, during its development climbs the ladder upon the rungs of which
the whole animal series is distributed, in its gradual progression from
simplicity to complexity. The law of development which he adopts is that
of von Baer, which states that development is essentially
differentiation, and that as a result embryos belonging to the same
group resemble one another the more the less advanced they are in
development. There can be little doubt that he was indebted to von Baer
for the idea, and in the later editions of the _Origin_ he acknowledges
this by quoting the well-known passage in which von Baer tells how he
had two embryos in spirit which he was unable to refer definitely to
their proper class among Vertebrates.[354]
Not only are embryos more alike than adults, because less
differentiated, but it is in points not directly connected with the
conditions of existence, not strictly adaptive, that their resemblance
is strongest (p. 440)--think, for instance, of the arrangement of aortic
arches common to all vertebrate embryos. Larval forms are to some extent
exceptions to this rule, for they are often specially adapted to their
particular mode of life, and convergence of structure may accordingly
result. All these facts require an explanation. "How, then, can we
explain these several facts in embryology--namely, the very general, but
not universal, difference in structure between the embryo and the
adult--of parts in the same individual embryo, which ultimately become
very unlike and serve for different purposes, being at this early period
of growth alike--of embryos of different species within the same class,
generally but not universally, resembling each other--of the structure
of the embryo not being closely related to its conditions of existence,
except when the embryo becomes at any period of life active and has to
provide for itself--of the embryo apparently having sometimes a higher
organisation than the mature animal, into which it is developed" (pp.
442-3). Obviously all these facts are formally explained by the doctrine
of descent. But Darwin goes further, he tries to show exactly how it is
that the embryos resemble one another more than the adults. He thinks
that the phenomenon results from two principles--first, that
modifications usually supervene late in the life of the individual; and
second, that such modifications tend to be inherited by the offspring at
a corresponding, not early, age (p. 444).
Thus, applying these principles to a hypothetical case of the origin of
new species of birds from a common stock, he writes:--"... from the many
slight successive steps of variation having supervened at a rather late
age and having been inherited at a corresponding age, the young of the
new species of our supposed genus will manifestly tend to resemble each
other much more closely than do the adults, just as we have seen in the
case of pigeons"[355] (pp. 446-7).
Since the embryo shows the generalised type, the structure of the embryo
is useful for classificatory purposes. "For the embryo is the animal in
its less modified state; and in so far it reveals the structure of its
progenitor" (p. 449)--the embryological archetype reveals the ancestral
form. "Embryology rises greatly in interest, when we thus look at the
embryo as a picture, more or less complete, of the parent form of each
great class of animals" (p. 450)--a prophetic remark, in view of the
enormous subsequent development of phylogenetic speculation.
We may sum up by saying that Darwin interpreted von Baer's law
phylogenetically.
The rest of the chapter is devoted to a discussion of abortive and
vestigial organs, whose existence Darwin naturally turns to great
advantage in his argument for evolution. Throughout the whole chapter
Darwin's preoccupation with the problems of classification is clearly
manifest.
On the question as to whether descent was monophyletic or polyphyletic
Darwin expressed no dogmatic opinion. "I believe that animals have
descended from at most only four or five progenitors, and plants from an
equal or lesser number.... I should infer from analogy that probably all
the organic beings which have ever lived on this earth have descended
from one primordial form, into which life was first breathed" (p. 484).
Darwin rightly laid much stress upon the morphological evidence for
evolution,[356] which he considered to be weighty. It probably contributed
greatly to the success of his theory. Though he himself did little or no
work in pure morphology, he was alive to the importance of such work,[357]
and followed with interest the progress of evolutionary morphology,
incorporating some of its results in later editions of the _Origin_, and
in his _Descent of Man_ (1871).
In his morphology Darwin was hardly up to date. He does not seem to have
known at first hand the splendid work of the German morphologists, such
as Rathke and Reichert; he pays no attention to the cell-theory, nor to
the germ-layer theory. His sources are, in the main, Geoffroy St
Hilaire, Owen, von Baer, Agassiz, Milne-Edwards, and Huxley.
Perhaps his greatest omission was that he did not give any adequate
treatment of the problem of functional adaptation and the correlation of
parts. It is not too much to say that Darwin not only disregarded these
problems almost entirely, but by his insistence upon ecological
adaptation and upon certain superficial aspects of correlation,
succeeded in giving to the words "adaptation" and "correlation" a new
signification, whereby they lost to a large extent their true and
original functional meaning.
It is true that Darwin himself, as well as his successors, believed that
natural selection was all-powerful to account for the evolution of the
most complicated organs, but it may be questioned whether he realised
all the conditions of the problem of which he thus easily disposed. He
says, rightly, in an important passage, that "It is generally
acknowledged that all organic beings have been formed on two great
laws--Unity of Type, and the Conditions of Existence. By unity of type
is meant that fundamental agreement in structure which we see in organic
beings of the same class, and which is quite independent of their habits
of life. On my theory, unity of type is explained by unity of descent.
The expression of conditions of existence, so often insisted upon by the
illustrious Cuvier, is fully embraced by the principle of natural
selection. For natural selection acts by either now adapting _the
varying parts of each being to its organic and inorganic conditions of
life_:[358] or by having adapted them during past periods of time: the
adaptations being aided in many cases by the increased use or disuse of
parts, being affected by the direct action of the external conditions of
life, and subjected in all cases to the several laws of growth and
variation. Hence, in fact, the law of the Conditions of Existence is the
higher law; as it includes, through the inheritance of former variations
and adaptations, that of Unity of Type" (_Origin_, 6th ed., Pop.
Impression, pp. 260-1). It is clear that Darwin took the phrase
"Conditions of Existence" to mean the environmental conditions, and the
law of the Conditions of Existence to mean the law of adaptation to
environment. But that is not what Cuvier meant by the phrase: he
understood by it the principle of the co-ordination of the parts to form
the whole, the essential condition for the existence of any organism
whatsoever (see above, Chap. III., p. 34).
Of this thought there is in Darwin little trace, and that is why he did
not sufficiently appreciate the weight of the argument brought against
his theory that it did not account for the correlation of variations.
Darwin's conception of correlation was singularly incomplete. As
examples of correlation he advanced such trivial cases as the relation
between albinism, deafness and blue eyes in cats, or between the
tortoise-shell colour and the female sex. He used the word only in
connection with what he called "correlated variation," meaning by this
expression "that the whole organisation is so tied together during its
growth and development, that when slight variations in any one part
occur, and are accumulated through natural selection, other parts become
modified" (6th ed., p. 177). He took it for granted that the "correlated
variations" would be adapted to the original variation which was acted
upon by natural selection, and he saw no difficulty in the gradual
evolution of a complicated organ like the eye if only the steps were
small enough. "It has been objected," he writes, "that in order to
modify the eye and still preserve it as a perfect instrument, many
changes would have to be effected simultaneously, which, it is assumed,
could not be done through natural selection; but as I have attempted to
show in my work on the variation of domestic animals, it is not
necessary to suppose that the modifications were all simultaneous, if
they were extremely slight and gradual" (6th ed., p. 226).
In post-Darwinian speculation the difficulty of explaining correlated
variation by natural selection alone became more acutely realised, and
it was chiefly this difficulty that led Weismann to formulate his
hypothesis of germinal selection as a necessary supplement to the
general selection theory.
The change in the conception of correlation which Darwin's influence
brought about has been very clearly stated by E. von Hartmann,[359] from
whom the following is taken:--"While the correlation of parts in the
organism was before Darwin regarded exclusively from the standpoint of
morphological systematics, Darwin tried to look at it from the
standpoint of physiological and genealogical development, and in so
doing he put the standpoint of morphological systematics in the shade.
But the more we are now beginning to realise that systematic
relationship does not necessarily imply genetic affinity the more must
the correlation of parts come back into favour as a systematic
principle. While Darwin only, as it were, against his will, relied on
the law of correlation as a last resort when all other help failed, this
law must be regarded, from the standpoint of the orderly inner
determination of all organic form-change, as having the rank of the
highest principle of all, a principle which rules parallel, divergent
and convergent evolution" (pp. 47-8).
Further on, following Radl, he characterises Darwin's attitude to the
law of correlation in these terms:--"Darwin's interest is entirely
focussed on the variation, the function, the causes of form-production,
in short, upon evolution. Accordingly he regards correlation essentially
as correlative variation in the sense of a _departure_ from the given
type. With morphological correlation in _different_ types Darwin
troubles himself not at all, nor with correlation in the normal
development of a type" (p. 49).
Cuvier's conception of the _convenance des parties_, essential to all
biology, remained on the whole foreign to Darwin's thought, and to the
thought of his successors.
It was indeed one of their boasts that they had finally eliminated all
teleology from Nature. The great and immediate success which Darwinism
had among the younger generation of biologists and among scientific men
in general was due in large part to the fact that it fitted in well with
the prevailing materialism of the day, and gave solid ground for the
hope that in time a complete mechanistic explanation of life would be
forthcoming. "Darwinismus" became the battle-cry of the militant spirits
of that time.
It was precisely this element in Darwinism that was repugnant to most of
Darwin's opponents, in whose ranks were found the majority of the
morphologists of the old school. They found it impossible to believe
that evolution could have come about by fortuitous variation and
fortuitous selection; they objected to Darwin that he had enunciated no
real _Entwickelungsgesetz_, or law governing evolution. They were not
unwilling to believe that evolution was a real process, though many drew
the line at the derivation of man from apes, but they felt that if
evolution had really taken place, it must have been under the guidance
of some principle of development, that there must have been manifested
in evolution some definite and orderly tendency towards perfection.[360]
No one expressed this objection with greater force than did von Baer, in
a series of masterly essays[361] which the Darwinians, through sheer
inability to grasp his point of view, dismissed as the maunderings of
old age. In these essays von Baer pointed out the necessity for the
teleological point of view, at least as complementary to the
mechanistic. His general position is that of the "statical"
teleology--to use Driesch's term--of Kant and Cuvier. His attitude to
Darwinism is determined by his teleology. He admits, just as in 1834, a
limited amount of evolution; he criticises the evolution theory of
Darwin on the same lines exactly as forty or fifty years previously he
had criticised the recapitulation and evolution-theories of the
transcendentalists--principally on the ground that their deductions far
outrun the positive facts at their disposal. He rejects the theory of
natural selection entirely, on the ground that evolution, like
development, must have an end or purpose (_Ziel_)--"A becoming without a
purpose is in general unthinkable" (p. 231); he points out, too, the
difficulty of explaining the correlation of parts upon the Darwinian
hypothesis. His own conception of the evolutionary process is that it is
essentially _zielstrebig_ or guided by final causes, that it is a true
_evolutio_ or differentiation, just as individual development is an
orderly progress from the general to the special. He believed in
saltatory evolution, in polyphyletic descent, and in the greater
plasticity of the organism in earlier times.
The idea of saltatory evolution he took from Koelliker, who shortly after
the publication of the _Origin_ promulgated in a critical note on
Darwinism a sketch of his theory of "heterogeneous generation."[362]
Koelliker's attitude is typical of that taken up by many of the
morphologists of the day.[363] He accepts evolution completely, but
rejects Darwinism because it recognises no _Entwickelungsgesetz_, or
principle of evolution. For the Darwinian theory of evolution through
the selection of small fortuitous variations he would substitute the
theory of evolution through sudden, large variations, brought about by
the influence of a general law of evolution. This is his theory of
heterogeneous generation. "The fundamental idea of this hypothesis is
that under the influence of a general law of evolution creatures produce
from their germs others which differ from them" (p. 181). It is to be
noticed that Koelliker laid more stress upon the _Entwickelungsgesetz_
than upon the saltatory nature of variation, for he says a few pages
further on--"the notion at the base of my theory is that a great
evolutionary plan underlies the development of the whole organised
world, and urges on the simpler forms towards ever higher stages of
complexity" (p. 184). Saltatory evolution was not the essential point of
the theory:--"Another difference between the Darwinian hypothesis and
mine is that I postulate many saltatory changes, but I will not and
indeed cannot lay the chief stress upon this point, for I have not
intended to maintain that the general law of evolution which I hold to
be the cause of the creation of organisms, and which alone manifests
itself in the activity of generation, cannot also so act that from one
form others quite gradually arise" (p. 185). He put forward the
hypothesis of saltatory variation because it seemed to him to lighten
many of the difficulties of Darwinism--the lack of transition forms, the
enormous time required for evolution, and so on. It should be noted that
Koelliker regarded his principle of evolution as mechanical.
It would take too long to show in detail how a belief in innate laws of
evolution was held by the majority of Darwin's critics. A few further
examples must suffice.
Richard Owen, who in 1868[364] admitted the possibility of evolution, held
that "a purposive route of development and change, of correlation and
interdependence, manifesting intelligent Will, is as determinable in the
succession of races as in the development and organisation of the
individual. Generations do not vary accidentally, in any and every
direction; but in pre-ordained, definite, and correlated courses" (p.
808).
He conceived change to have taken place by abrupt variation, independent
of environment and habit, by "departures from parental type, probably
sudden and seemingly monstrous, but adapting the progeny inheriting such
modifications to higher purposes" (p. 797). He believed spontaneous
generation to be a phenomenon constantly taking place, and constantly
giving the possibility of new lines of evolution.
E. von Hartmann in his _Philosophie des Unbewussten_ (1868) and in his
valuable essay on _Wahrheit und Irrtum im Darwinismus_ (1874) criticised
Darwinism in a most suggestive manner from the vitalistic standpoint. He
drew attention to the importance of active adaptation, the necessity for
assuming definite and correlated variability, and to the evidence for
the existence of an immanent, purposive, but unconscious principle of
evolution, active as well in phylogenetic as in individual development.
In France H. Milne-Edwards[365] stated the problem thus:--"In the present
state of science, ought we to attribute to modifications dependent on
the action of known external agents the differences in the organic types
manifested by the animals distributed over the surface of the globe
either at the present day, or in past geological ages? Or must the
origin of types transmissible by heredity be attributed to causes of
another order, to forces whose effects are not apparent in the present
state of things, to a creative power independent of the general
properties of organisable matter such as we know them to-day?" (p. 426)
He concluded that the action of environment, direct or indirect, was
insufficient to account for the diversity of organic forms, and rejected
Darwin's theory completely. He thought it likely that the successive
faunas which palaeontology discloses have originated from one another by
descent. But he thought that the process by which they evolved should
rightly be called "creation." The word was of course not to be taken in
a crude sense. When the zoologist speaks of the "creation" of a new
species, "he in no way means that the latter has arisen from the dust,
rather than from a pre-existing animal whose mode of organisation was
different; he merely means that the known properties of matter, whether
inert or organic, are insufficient to bring about such a result, and
that the intervention of a hidden cause, of a power of some higher
order, seems to him necessary" (p. 429).
The criticism of Darwinism exercised by the older currents of thought
remained on the whole without influence. It was under the direct
inspiration of the Darwinian theory that morphology developed during the
next quarter of a century.
[333] Radl, _loc. cit._, i., p. 71.
[334] _Kritik der Urtheilskraft_, 1790.
[335] Eng. Trans. by J. H. Bernard, p. 337, London, 1892.
[336] H. F. Osborn, _From the Greeks to Darwin_, p. 145,
New York and London, 1894.
[337] See Meckel, _supra_, p. 93; _cf._ Tiedemann,
_Zoologie_, p. 65, 1808. "Even as each individual
organism transforms itself, so the whole animal kingdom
is to be thought of as an organism in course of
metamorphosis." Also p. 73 of the same book.
[338] Chapters vii. and ix.
[339] On early evolution-theories see, in addition to
Osborn and Radl, J. Arthur Thomson, _The Science of
Life_, 1899, and the opening essay in _Darwin and Modern
Science_, Cambridge, 1909.
[340] _Phil. zool._, ed. Ch. Martins, vol. i., p. 75,
1873.
[341] Quotations in the text are from the 2nd Edit.
(Deshayes and Milne-Edwards), i., Paris, 1835.
[342] For instance, Lucretius:--
"Is tibi nunc animus quali sit corpore et unde
constiterit pergam rationem reddere dictis. Principio
esse aio persubtilem atque minutis perquam corporibus
factum constare."
--_De Rerum Natura_, iii., vv. 177-80.
[343] Contrast Treviranus--"In every living being there
exists a capability of an endless variety of
form-assumption; each possesses the power to adapt its
organisation to the changes of the outer world, and it
is this power, put into action by the change of the
universe, that has raised the simple zoophytes of the
primitive world to continually higher stages of
organisation, and has introduced a countless variety of
species into animate Nature." Quoted by Haeckel in
_History of Creation_, i., p. 93, 1876.
[344] There is no evidence that he was influenced by
Erasmus Darwin, who forestalled his evolution theory, and
was indeed more aware of its vitalistic implications. See
S. Butler, _Evolution, Old and New_, London, 1879, for an
excellent account of Erasmus Darwin.
[345] As did also Lyell in his _Principles of Geology_,
1830.
[346] K. E. von Baer, _Reden_, i., p. 37, Petrograd, 1864.
[347] Radl, _loc. cit._, i., p. 296.
[348] Reprinted in his _Reden_, i., 1864.
[349] See Huxley's criticism of it in a Royal Institution
lecture of 1851, republished in _Sci. Mem._, i., pp.
300-4. On its relation to Haeckel's biogenetic law, see
below, p. 255.
[350] _System der thierischen Morphologie_, p. 5, 1853.
[351] _Life and Letters of Charles Darwin_, ed. F. Darwin,
i., p. 82, 3rd ed., 1887.
[352] _The Foundations of the Origin of Species, a Sketch
written in 1842_. Ed. F. Darwin, Cambridge, 1909.
[353] _Cf._ a parallel passage in the _Origin_, 1st ed.,
pp. 485-6.
[354] In the 1st ed. (p. 439), Darwin makes the curious
mistake of attributing this story to Agassiz.
[355] In which nestlings of the different varieties are
much more alike than adults. Darwin attached much
importance to this idea, see _Life and Letters_, i., p.
88, and ii., p. 338.
[356] See his _Letters, passim_.
[357] Writing to Huxley on the subject of the latter's
work on the morphology of the Mollusca (1853), he
says:--"The discovery of the type or 'idea' (in your
sense, for I detest the word as used by Owen, Agassiz &
Co.) of each great class, I cannot doubt, is one of the
very highest ends of Natural History."--_More Letters_,
ed. F. Darwin and A. C. Seward, 1903, i., p. 73.
[358] Italics mine.
[359] _Das Problem des Lebens. Biologische Studien_. Bad
Sacha, 1906. See also E. Radl, _Biol. Centralblatt_,
xxi., 1901.
[360] See the excellent treatment of the difference
between the "realism" of Darwin and the "rationalism" of
his critics, in Radl, ii., particularly pp. 109, 135.
The most elaborate criticism of Darwinism from the older
standpoint was that given by A. Wigand in _Der
Darwinismus und die Naturforschung Newtons und Cuviers_,
3 vols., Braunschweig, 1872.
[361] In vol. ii. of his _Reden_, St Petersburg
(Petrograd), 1876--_Ueber den Zweck in den Vorgaengen der
Natur; Ueber Zielstrebigkeit in den organischen Koerpern
insbesondere_; and _Ueber Darwin's Lehre_.
[362] "Ueber die Darwinische Schoepfungstheorie," _Zeits.
f. wiss. Zool._, xiv., pp. 74-86, 1864. Elaborated in
_Anat. u. syst. Beschreibung d. Alcyonarien_, 1872.
[363] _Cf._ for instance Naegeli's theory of a perfecting
principle, first developed in his _Entstehung u. Begriff
der naturhistorischer Art_, Muenchen, 1865.
[364] _Anatomy of Vertebrates_, iii., 1868.
[365] _Rapport sur les Progres recents des Sciences
zoologiques en France_. Paris, 1867.