Form and Function
E >>
E. S. (Edward Stuart) Russell >> Form and Function
Pages:
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 | 21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
30 |
31 |
32 |
33
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.
CHAPTER XIV
ERNST HAECKEL AND CARL GEGENBAUR
At the time when Darwin's work appeared there already existed, as we
have seen, a fully formed morphology with set and definite principles.
The aim of this pre-evolutionary morphology had been to discover and
work out in detail the unity of plan underlying the diversity of forms,
to disentangle the constant in animal form and distinguish from it the
accessory and adaptive. The main principle upon which this work was
based was the principle of connections, so clearly stated by Geoffroy.
The principle of connections served as a guide in the search for the
archetype, and this search was prosecuted in two directions--first, by
the comparison of adult structure; and second, by the comparative study
of developing embryos. It was found that the archetype was shown most
clearly by the early embryo, and this embryological archetype came to be
preferred before the archetype of comparative anatomy. It became
apparent also that the parts first formed (germ-layers) were of primary
importance for the establishing of homologies.
While practically all morphologists were agreed as to the main
principles of their science, they yet showed, as regards their general
attitude to the problems of form, a fairly definite division into two
groups, of which one laid stress upon the intimate relation existing
between form and function, while the other disregarded function
completely, and sought to build up a "pure" or abstract morphology. In
opposition to both groups, in opposition really to morphology
altogether, a movement had gained strength which tended towards the
analysis and disintegration of the organism. This movement took its
origin in the current materialism of the day, and found expression
particularly in the cell-theory and in materialistic physiology.
The separation between morphology as the science of form and physiology
as the science of the physics and chemistry of the living body had by
Darwin's day become well-nigh absolute.
The morphology of the 'fifties lent itself readily to evolutionary
interpretation. Darwin found it easy to give a formal solution of all
the main problems which pre-evolutionary morphology had set--he was able
to interpret the natural system of classification as being in reality
genealogical, systematic relationship as being really
blood-relationship; he was able to interpret homology and analogy in
terms of heredity and adaptation; he was able to explain the unity of
plan by descent from a common ancestor, and for the concept of
"archetype" to substitute that of "ancestral form."
The current morphology, Darwin found, could be taken over, lock, stock
and barrel, to the evolutionary camp.
In what follows we shall see that the coming of evolution made
surprisingly little difference to morphology, that the same methods were
consciously or unconsciously followed, the same mental attitudes taken
up, after as before the publication of the _Origin of Species_.
Darwin himself was not a professional morphologist; the conversion of
morphology to evolutionary ideas was carried out principally by his
followers, Ernst Haeckel and Carl Gegenbaur in Germany, Huxley,
Lankester, and F. M. Balfour in England.
It was in 1866 that Haeckel's chief work appeared, a _General Morphology
of Organisms_,[366] which was intended by its author to bring all
morphology under the sway and domination of evolution.
It was a curious production, this first book of Haeckel's, and
representative not so much of Darwinian as of pre-Darwinian thought. It
was a medley of dogmatic materialism, idealistic morphology, and
evolution theory; its sources were, approximately, Buechner, Theodor
Schwann, Virchow, H. G. Bronn, and, of course, Charles Darwin.
It was scarcely modern even on its first appearance, and many regarded
it, not without reason, as a belated offshoot of _Naturphilosophie_.
Its materialism is of the most intransigent character. The form and
activities of living things are held to be merely the mechanical result
of the physical and chemical composition of their bodies. The simplest
living things, the Monera, are nothing more than homogeneous masses of
protein substance. "They live, but without organs of life; all the
phenomena of their life, nutrition and reproduction, movement and
irritability, appear here as merely the immediate outcome of formless
organic matter, itself an albumen compound" (p. 63, 1906).
Teleology, the Achilles' heel of Kant's (otherwise sound!) philosophy,
is to be regarded as a totally refuted and antiquated doctrine,
definitely put out of court by Darwinism.
Haeckel works out his materialistic philosophy of living things very
much after the fashion of Schwann. There is the same talk of cells as
organic crystals, of crystal trees, of the analogy between assimilation
by the cell and the growth of crystals in a mother liquid. Heredity and
adaptation are shown equally as well by crystals as by organisms; for
heredity, or the internal _Bildungstrieb_ (!), is the mechanical effect
of the material structure of the crystal or the germ, and adaptation, or
the external _Bildungstrieb_, is a name for the modifications induced by
the environment. Adaptation so defined comes to be synonymous with the
fortuitous variation which plays so great a part in Darwin's theory of
natural selection.
It goes without saying that Haeckel allowed to the organism no other nor
higher individuality than belongs to the crystal, and took no account at
all of that harmonious interaction of the organs which Cuvier called the
principle of the "conditions of existence." The concept of correlation
had simply no meaning for Haeckel. The analysis and disintegration of
the organism was pushed by him to its logical extreme, and in this also
he was a child of his time.
A no less important influence clearly visible in the _General
Morphology_ is the idealistic morphology of men like K. G. Carus and H. G.
Bronn. In previous chapters we have seen how K. G. Carus attempted to
work out a geometry of the organism, and how Bronn tried in a modest way
to found a stereometrical morphology, but had the grace not to push his
stereometry _a l'outrance_, recognising very wisely that the greater
part of organic form is functionally determined. Haeckel took over this
idea[367] and pushed it to wild extremes, founding a new science of
"Promorphology" of which he was the greatest--and only--exponent.[368]
This "science" dealt with axes and planes, poles and angles, in a
veritable orgy of barbarous technical terms. It was intended to be a
"crystallography of the organic," and to lay the foundations of a
mechanistic morphology, or morphography at least.
How it was to be linked up with the physics and chemistry of living
matter on the one hand and with the ordinary morphology of real animals
on the other, was never made quite clear.
The science of Promorphology has no historical significance; it is
interesting only because it illustrates Haeckel's close affinity with
the idealistic morphologists.
Another abortive science of Haeckel's, the science of Tectology, was
equally a heritage from idealistic morphology. Tectology is the science
of the composition of organisms from individuals of different orders.
There were six orders of individuals:--(1) Plastids (Cytodes and cells);
(2) Organs (including cell-fusions, tissues, organs, organ-systems); (3)
Antimeres (homotypic parts, _i.e._, halves or rays); (4) Metameres
(homodynamic parts, _i.e._, segments); (5) Persons (individuals in the
ordinary sense); (6) Corms (colonial animals).
The thought is essentially transcendental, and recalls the "theory of
the repetition of parts," of which so much use was made by the German
transcendentalists, such as Goethe,[369] Oken, Meckel and K. G. Carus, as
well as by Duges.
The third, and naturally the most important, ingredient in the _General
Morphology_ was the doctrine of evolution, in the form given to it by
Darwin. We have here no concern with Haeckel's evolutionary philosophy,
with the way in which he combined his evolutionism and his materialism
to form a queer Monism of his own. We are interested only in the way he
applied evolution to morphology, what modifications he introduced into
the principles of the science, and in general in what way he interpreted
the facts and theories of morphology in the light of the new knowledge.
We find that he repeats very much what Darwin said, giving, of course,
more detail to the exposition, and elaborating, particularly in his
recapitulation theory or "biogenetic law," certain doctrines not
explicitly stated by Darwin.
Pages:
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 | 21 |
22 |
23 |
24 |
25 |
26 |
27 |
28 |
29 |
30 |
31 |
32 |
33