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Vernon L. (Vernon Lyman) Kellogg.

Darwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming online

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Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 19 of 38)
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we need say little. It consists of two purely speculative basic
assumptions : First, Weismann's particular theory of the
ultimate structure of the germ-plasm, namely, the theory of
biophors and determinants; and secondly, the assumption
that there is a struggle for food among the determinants.
There is no proof of pure observation or experiment for
the theory, and there is some proof directly against it. And
yet the great need of a working hypothesis for the causo-
mechanical explanation of determinate variation makes us
give such a pure speculation more attention than it might
otherwise get. Unfortunately the attention thus given to
this particular theory seems to have resulted in the bringing
forward of some rather serious objections to the possibility



2 oo DARWINISM TO-DAY.

of the truth of the theory. A few of these objections ' may
be briefly stated.

According to the theory there should be plainly exhibited

in the variation of any species, decided tendencies in certain

Objections to specific directions. In all species, in all indi-

theoryofger- v iduals, the struggle of the determinants must

minal selec-
tion, result in the suppression or reduction of some,

the extra-development of others. Thus variation should
not reveal itself according to the law of error, that is, should
not be distributed normally about a mean or mode. But
that is exactly the condition of variation in a majority of
those cases in which the variation of one or more organs
in any species has been statistically studied. The plotted
curve of any particular variation of this type is a symmetri-
cal curve nearly coincident with the theoretical one express-
ing the law of error for the same case.

The constancy of species is just as marked and actual a
condition as the condition of slight fluctuating variations
inside the species. This constancy is steadfast for con-
siderable time-periods. But with such an active orthogene-
sis as the theory of germinal selection provides, there could
be no such steadfast constancy. Weismann himself recog-
nised the weight of this objection to the theory, and speaks
of an attribute of "self-correction" pertaining to the germ-
plasm, which shall regulate or check too rapid an ortho-
genetic development.

The actual change of the competitive determinants due
to their obtaining an over or under supply of food should
be one simply quantitative in degree ; such germinal selec-
tion could thus lead to the change in size and strength of
organs already present in the species, but could offer no
explanation of qualitative changes, i. e., the appearance of
new kinds of structures. Moreover, even in cases of purely
quantitative change, such familiar cases as the persistence
through long time-periods of small, rudimentary organs,



OTHER THEORIES OF SPECIES-FORMING. 201

without any indication of further reduction, indicate a pecu-
liar cessation in the forthright working of germinal selec-
tion. Why should not the weak determinants of these weak
organs go completely to ground in the struggle ?

Actual experimentation on the influence of food-supply
in development does not bear out the assumption on which
the* theory of germinal selection rests. Weismann himself
gave the larvae of flies, and I have given the larvae of silk-
worms through their whole life-time, an abnormally small
food supply (in the case of the silkworm's this supply was-
from one-fourth to one-eighth the amcmnt normally eaten
by full-fed larvae), with the only result that the mature
individuals were dwarfed ; that all their parts were reduced
in size, but the actual size proportions of the various organs
and parts, and their relations to each other, were unchanged.
The determinants seemed to share equally the hardships of
short rations rather than a few of the stronger getting the
better of the weaker. From the eggs of birds considerable
quantities of yolk have been withdrawn without modifying
appreciably the individuals developed from the eggs.

If the struggle of the determinants is really an actual and
severe one then only those of the large strong organs should
survive, all the others being starved out. Such a condition
would result in the exclusive development of monsters, i. e.,
individuals lacking numerous organs (the small ones), and
with the large ones all over-developed.

Roux's Theory of Infra-selection or the Battle of the
Parts. Distinctly more likely to appeal to our reason is the
theory of Roux, 7 proposed in 1881, to explain how one or
more organs may exhibit a progressive development or
increase in size and capacity without reference to natural
selection and also to account for the many remarkable adap-
tations of slight and delicate but extremely precise character
exhibited by various internal organs. Roux made, however,
a too radical distinction between external or superficial



202 DARWINISM TO-DAY.

adaptations on the one hand, attributing these to the influ-
ence of natural selection, and the adaptations of internal
parts on the other, which he would attribute to the influ-
ence of his functional stimuli and of his struggle among
the inner parts of the body. This struggle, like that among
Weismann's hypothetical determinants, is one chiefly for
food, but in Roux's theory there is no assumption of hypo-
thetical life units, nor any lack of clearness concerning the
initiation of the actual struggle. The competing parts in
Roux's theory are the chemical molecules composing the
The competing cell > the ce ^ s themselves, groups or tissues of
parts in BOM'S cells, and even whole organs. The spurs to the
luy^ognS" competition for food are functional stimuli,
structures. whose result is to set up a special demand and
necessity for more food. Roux's classic example will make
this clear. It is a matter of fact that the fine plates and
layers of bone in the "spongy tissue" of the long bones of
the body, are so disposed as actually best to withstand the
stresses most usually brought to bear on the bones. Thus
they show a fine adaptation of arrangement, which one meets
difficulties in trying to explain as due to natural selection.
For, if we imagine the thin plates of the spongy tissue
purely miscellaneously arranged, the possible slight varia-
tions whereby a few plates at a time might fortuitously
occur in a position or direction better fit to strengthen the
whole bone, are so insignificant in proportion to the condi-
tion throughout all the rest of the bone that we cannot possi-
bly attribute to them a life-and-death value in the individual's
struggle for existence. Roux assumes that the stresses
brought to bear on the bone during its development act as
functional stimuli to all those plates in the forming spongy
tissue, which lie in such places or at such an angle to the
stress as to be affected by them, and in response to these
stimuli, which in Roux's belief are necessary to the normal
structural development and maintenance of any part, these



OTHER THEORIES OF SPECIES-FORMING. 203

forming bony plates will take up more food than the un-
stimulated ones, and thus will be developed at
the ex Pense of these others. Similarly with
11 those other marvellously delicate inner adap-
tations of fine and minute and oft-repeated structures to the
spesial functions of the organs containing these structures.
The stimulus of the function excites a trophic demand on
the part of the struggle and an actual capacity for satisfying
the demand, that soon leads to the extra-development of
the stimulated parts at the expense of adjacent similar parts
deriving food from the supply common to all. Thus Roux
would explain the exquisite adaptation of the arrange-
ment of the muscle-fibres in the walls of the blood-vessels,
the tsenidia or spiral threads in the tracheae of insects, the
little barbs on the feathers of birds which hold these feathers
together in almost air-tight continuity, the numerous protect-
ive hairs covering the spiracles of many insects, etc., etc.

It will be noted that the competition of the parts is really
twofold ; thus, while for successful development it is neces-
sary for parts to be successful in food-getting,
of the parts is this success in food-getting seems to depend
twofold. U p 0n tne prerequisite of receiving a needed

functional stimulus. Thus there may be said to exist a com-
petition for functional stimuli. But obviously success in
this competition depends chiefly on the hazard of position.
Those plates in the forming spongy tissue of a long bone
which happen to lie where the stress comes, and in a special
direction to be affected by it, are the winners in the compe-
tition for stimuli.

Roux's theory has appealed strongly to many biologists,
but others have rejected it wholly, or at least as an explana-
tion of fine inner adaptations. Plate takes this

Plate's criti-
cism of Bonx's latter position, but finds a great service in the

theory. theory in that "Roux has given in it a profound

analysis of the well-known fact that use strengthens and



204 DARWINISM TO-DAY.

disuse weakens. His is the great merit of having clearly
explained the extraordinary importance (Tragweite), in the
building of new forms and adaptive structures, of this ele-
mentary attribute of organisms. We have to thank him for
the best putting together of all those observations which
permit of but the one conclusion, that the functional stimuli
exercise a trophic activity, that is, that each organ by the
constant exercise of its function becomes stimulated to
stronger assimilation and increased multiplication of its
elementary parts, and that out of this there results a height-
ened functional capacity." However, as Plate points out,
The law of tms " law f functional adaptation" does not
functional adap- apply to all organs and tissues; "the teeth of

tation does not

apply to all many mammals become impaired through con-
organs, stant use, and most of the sense-organs are
apparently not bettered through use in regard to their per-
ceiving elements but only in regard to their carrying ele-
ments. Every exercise is followed by a certain fatigue
which, in cases of exhaustion, is greater than the aimed at
(erzielte} increase of functional capacity. Also the trophic
stimulation can, in certain cases, lead to hypertrophy and
other unadaptive results." But as regards the actual "strug-
gle of the parts," and especially as regards the claim that
such a struggle is to account for inner adaptations, Plate, as
a consistent natural selectionist, is wholly sceptical. He
offers five objections to any usurpation of the functions of
natural selection by this intra-selection theory. First, he
holds, with Wolff, that it is impossible to place the inner
adaptations in any sharp contrast with outer adaptations.
They are contrasted only in that the former stand in a more
indirect relation to the conditions of life. Indeed a single
organ, as a claw for example, can show an external adaptive-
ness in that it might be especially well arranged to scratch
hard dry ground, and at the same time be distinctly adap-
tively constructed as regards its fine inner structure. "If



OTHER THEORIES OF SPECIES-FORMING. 205

natural selection," says Plate, "is capable of producing outer
adaptations such as making the fur of a mammal thicker
and thicker as a protection against the cold, why can it not
increase, or if advantage lies the other way, decrease, the
number of bony plates in the spongy tissue of the long
bones ?"

Second, the capacity of living substance to be stimulated
to increased food-getting is an elementary attribute of organ-
isms just as the capacities to assimilate, to be

Trophic stimu- . t ' t

lationnotex- irritable, and to breathe are. This special
plained. capacity is not explained by the theory of intra-

selection; it is, indeed, just now wholly inexplicable. One
might perhaps fairly assume that it is the result of a gradual
development from the Protozoa onward, through the influ-
ence of individual selection. But this is no explanation of its
origin. Roux, himself, indeed, expressly declares that he
bases his theory on the proved but not explained fact of
functional adaptiveness, but some of his followers often
forget this and seem to claim that the distinctly advantage-
ous peculiarity of most tissues to be able to increase in
strength and size through use is a direct result of the
battle of the parts.

Third, Plate holds that the battle of the parts plays no
role in ontogeny. The cleavage and embryonal develop-
ment are wholly controlled by heredity, so that
parts not evident there is nothing left for the battle of the parts.
in ontogeny, There occurs a peaceful and regular split-
ting apart of the single cells and a separation of them
according to their different qualities, and it does not at all
occur that the strongest cells get all the food and the weak-
est none, but on the contrary each receives as much as it
needs for its growth. In a blastula of thirty-two cells it is
not the capacity on the part of certain cells which results in
the stronger growth of some and the weaker growth of
others, or the more rapid multiplication of some and the



206 DARWINISM TO-DAY.

less rapid of others, but, on the contrary, for each species
there is a definite law of growth which we may only explain
as the expression of a force of heredity, not capable yet of
analysis. Matters certainly do not go on in an embryo as
in an agar culture containing several kinds of bacteria of
which only that one with the greatest life force remains.
Were the development of the embryo determined by the
food-zeal of the cleavage cells, it would happen that in a
short time a few cells specially capable of assimilation would
get the upper hand, and as a consequence only a few quali-
ties be left to the embryo; a real differentiation into thou-
sands of different cell-sorts would not be possible. All the
facts of symmetry and auto-regulation in embryonic develop-
ment speak against any considerable influence of a battle of
the parts during development.

Fourth, Plate declares that in the acquirement of new
characters no selective intra-struggle takes place, or at least

in only most insignificant manner, but that the
No battle of ... ,.

the parts in the new structures arise either through the direct

acquirement of influence of new stimuli or by natural selection

new characters. . ....

of new germinal variations of unknown origin.
In the first place it is simply the matter of position, not at
all that of quality, that decides whether the certain cells
shall be changed or not. Think, for example, of a vessel
in whose walls the connective tissue fibres cross and recross
in all directions wholly without order, and conceive that a
constant or repeated stress in both longitudinal and trans-
verse directions is exerted oh this vessel. It would result
that all those fibres lying in the absolute or approximate
directions of these stresses would be most stretched and
would in consequence of their trophic irritability most rapidly
enlarge and increase with special rapidity. Now by the
repetition and inheritance of this result of use it would finally
come about in the course of generations that all the fibres
situated in other directions to the stresses would die out,



OTHER THEORIES OF SPECIES-FORMING. 207

and thus a definite longitudinal and transverse arrangement
of fibres in the walls of the vessel result. Without doubt,
holds Plate, much advance is won in this way, but this
specialisation of structure is not a result of intra-struggle
but rests on the elementary attribute of trophic irritability.
Not the best-qualified but the best-situated fibres have van-
quished the others by robbing them of food and thus finally
destroying them. In the second place, "many inner struc-
tures belong to the great category of passive adaptations;
they function only through their presence and cannot thus
be further developed by use or disuse, that is, by functional
stimuli, but only by natural selection. Here belong, for
example, the stratification of the lens in the human eye, the
apodemes (inner projections of the chitinised cuticula)
which protect the ventral nerve-cord of the crabs, the chitin
hooks which hold together the fore and hind wings of many
insects, and the similar structures which bind together the
secondary branches of the feather vanes of birds. These
inner adaptations cannot have resulted through the influence
of light or of nervous function or flight. There is but one
explanation possible ; namely, that natural selection has
seized on and developed fortuitously appearing germinal
variations. But if natural selection can produce such inner
adaptations why can it not then produce all the others?"

Fifth, Plate points out that Roux's theory is based on the
inheritance of those special body characters which are
acquired through the battle of the parts more
Boux'stheory rightly, Plate holds, through functional adapta-
is to accept the tion, so that to accept the theory, one has to
acquired char- declare, to that degree, a belief in the inherit-
acterSl ance of acquired characters. Thus from the

start, the neo-Darwinians cannot accept the theory.

After all what is this theory of Roux's but a refinement, a
special case, of the broader and more general long-known
Lamarckian theory of the modifying and formative influ-



208 DARWINISM TO-DAY.

ence of use and disuse, accumulated through inheritance?

That is, if we accept Plate's analysis that the theory is

really not one of a battle of the parts, but of

the l^thewy the effects of functional stimuli. And however



is a special me fa Q p rO p Ose r of the theory may protest against
such an apparent violent setting over of it from
the category of selection (Darwinian) theories into that of
the inheritance of use (Lamarckian) theories, I believe that
most of us will see the justness of Plate's analysis. I do
not believe that Roux's theory in any way strengthens the
selection conception. To my mind, indeed, it is simply a
concession of the inadequacy of selection to initiate adapta-
tion, and a welcome and satisfying explanation of how such
an initiation may occur in many cases, in certain cases, that
is, of active adaptations. Plate's argument that natural
selection must be the only explanation for the cases of
passive adaptations and hence may be held capable for
accounting for the active ones, has no conviction for me, for
I do not believe that natural selection is the only possible
explanation of the passive cases. In fact, I cannot conceive
it to be a possible explanation of the initiation of these cases.
And I am glad to find in Roux's theory even if it be not
exactly applied in Roux's own sense a mechanical expla-
nation of the possibility of initiating certain fine and delicate
inner adaptations.

Organic Selection. An interesting attempt to escape from
the difficulties which are imposed on one by an absolute
adherence to Weismann's doctrine of the impos-
, sibility of the inheritance of acquired characters
cou P led with a belief in th e inadequacy of the
slight fluctuating germinal variations to afford
handles for the action of natural selection, is the theory va-
riously called organic selection, or orthoplasy, proposed by
Baldwin' and Osborn* in America, and Lloyd Morgan 10 in
England. This theory, which might also be called one of



OTHER THEORIES OF SPECIES-FORMING. 209

"ontogenetic selection," or of "coincident selection," is that
the personal selection, or individual survival, among indi-
viduals of a species does not necessarily depend solely upon
congenital variation but may, must, indeed, depend on any
ontogenetically acquired adaptations as well. As in many
cases these ontogenetic adaptations are considerable, they
will often carry individuals through very critical periods in
their lives. But the individuals showing these ontogenetic
adaptations in best degree will be those which actually pos-
sess certain slight congenital variations, especially of the
nervous system or coordinating nerve centres, "which lend
themselves to intelligent initiative, adaptive, or mechanical
modification during the lifetime of the creatures which have
them." The ontogenetic adaptations may occur regularly
in the lives of successive generations of individuals if the
environment remains fairly constant. During these suc-
cessive generations the congenital variations of brain, say,
which make the successful ontogenetic adaptations possible,
will by selection of the best ontogenetically Varying individ-
uals be themselves selected, and the species thus gradually be
modified in a determinate direction. Also congenital varia-
tions of nearly the same nature as the ontogenetic variations,
or of a nature to supply the same need, will have time (that
is, more chance, because of the longer time and repeated
generations) to appear. In this case these advantageous
variations can be transmitted directly by heredity, and thus
a permanent adaptation be effected which will seem to be the
result of the inheritance of an acquired character (i. e., the
similar ontogenetic modifications) but which in reality is
only the normal inheritance of a congenital variation.

In the language of all the sponsors for this theory there
seems to be a suggestion of the piling up or adding together
of congenital variations, not simply those of brain or other
control centre which make the ontogenetic modifications
possible, but also of these modifications themselves during the



2io DARWINISM TO-DAY.

successive generations through which the species is safely
carried by the temporary regularly appearing ontogenetic
adaptations. But there is nothing in strict neo-Darwinism
to permit of any such idea of increase. Such moving for-
ward without the aid of selection can only be explained by
the adoption of some theory of orthogenesis. Either the con-
genital variations are of such a character that the resulting-
ontogenetic modifications are not fairly to be distinguished
from them, in which case they are assumed to be large
enough from the start to afford handles for natural selection
(which the proposers of the theory are not claiming), or
they depend for their preservation on a kind of happy coinci-
dence in occurrence with similar more effective ontogenetic
modifications which are really large enough to save the life
of the organism and hence the slight congenital variations
along the same line. But in this latter case organic selection
cannot demand much discussion until it explains away a
Deluge and radical failing pointed out clearly by Delage

rf^'i i Sr i and plate - This is sim p ] y that > in the face of

turn. the large character which ontogenetic adapta-

tion may and often does possess, those individuals in which
the slight congenital variations in the right direction finally
appear will have no special advantage over those in which
they do not appear ; the large and effective character of the
ontogenetic adaptations, which are common to both kinds of
individuals, being quite sufficient to determine the result of
personal selection. The congenital variations will be too
small in comparison with the ontogenetic variations to cut
any figure in the fate of the individuals, and there is no
reason at all to believe that individuals showing the slight
congenital variations in the right direction will be the only
ones to show the saving large ontogenetic adaptations.
Plate suggests the following case to show the inutility of
this theory : Suppose an antelope species to have a leg muscle
averaging seven cm. in thickness, and several individuals to



OTHER THEORIES OF SPECIES-FORMING. 211

show a congenital variation bringing the leg muscle up to
eight cm. of thickness. Now if it requires a leg muscle of
eight cm. for safety, as a matter of fact almost all the indi-
viduals of the species will quickly bring their leg muscles up
to that size by use. But suppose the actual need for safety
was a leg muscle of fourteen cm., then only those individuals
specially capable of that ontogenetic adaptation, i. e. (modi-
fication of the leg muscle by use and trophic irritability), up
to fourteen cm., would be saved ; and undoubtedly among
these the original eight cm. individuals ought to stand in
slightly higher numerical proportion (in regard to their
original numerical standing in the species) than the origi-
nally seven cm. individuals. Since, however, these eight cm.
individuals originally existed only in comparatively small
number, and since they possess no special means of recognis-



Online LibraryVernon L. (Vernon Lyman) KelloggDarwinism to-day; a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxilary and alternative theories of species-forming → online text (page 19 of 38)