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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 15 of 38)
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since no individual is completely adapted to its environment,
it follows that there must be always a variable amount of
residual unfavourable variability in every organism.

"3. This residual unfavourable variability may be of con-
siderable utility under changed conditions.

"4. Complementary specialisation of parts, as Spencer
has shown, is favourable to successful competition, and as it
is the whole organism that is selected or eliminated, it fol-
lows that any weakness of one specialised part, since it would
disturb the balance of all, would be detrimental. The more
complex the organism, the more specialised the structures,
the more dependent one part will be on the others for its
existence, hence a complementary specialising tendency will
be favoured by selection, and therefore all struggles of one
part of an organism with another will be reduced to a
minimum.

"It is clear that there must be some underlying criterion
which determines whether any given organism shall be
selected or not, and that criterion must be the net result of
its adaptability to its environment. One organism may con-
ceivably survive, by its possession of a large number of small



, 54 DARWINISM TO-DAY.

favourable variations, while another may survive in virtue
of a single valuable one, but in each case it would be the
whole value of that organism which determined its survival.
This fact is continually disregarded by opponents of the
neo-Darwinian position, yet this selection of the organism
as a whole is the fundamental postulate from which the
theory of selection starts. Thus it is not uncommon to
read criticisms bearing on the early development of some
organ, in which the inadequacy of selection is supposed to
be proved by the writer demonstrating, or believing he has
demonstrated, the fact that the particular variation in ques-
tion must have been too small to be by itself of selection
value. In many cases the particular variation would, no
doubt, if taken alone be, as the objector asserts, too unim-
portant to be selected, but as it is the whole organism that
is selected, it is not logical to make an artificial separation
and study the development of one organ or structure irre-
spective of the other organs with which it is in nature asso-
ciated. Every organ in its evolution must be considered in
relation to the whole of the particular organism in which
that particular stage of development of that organ is found.
Starting, therefore, with this fact that the net value of
adaptability of the whole organism to its environment must
be the basis which determines selection or elimination, it
will follow that certain lines of development will result from
the application of this criterion. In a series of organisms
placed under new conditions, elimination will proceed along
lines essential to bring about a proper adjustment to the
new conditions. If the offspring of these adjusted organ-
isms merely repeated in their generation the characters of
the exterminated as well as of the surviving organisms,
that temporary adjustment would be permanent as long as
the conditions were unchanged. But since the offspring are
produced only by the surviving organisms, selection is con-
tinually raised to higher and higher planes of adaptation.



DARWINISM DEFENDED. 155

and, therefore, as long as conditions remain constant, the
tendency of selection must be, as Darwin clearly saw, cumu-
lative. He did not, however, apparently see that from this
cumulative tendency definite variability must arise out of
indefinite.

"Selection in direct relation to climatic conditions is, there-
fore, of very minor importance, while selection among the
members of a species and all forms of inter-organismal
selection is of infinitely more importance, since it is this
interaction, produced by the offspring in different degrees
inheriting the advantages of both parents (both of whom
have survived on account of certain advantages), that leads
to the cumulative development and never-ending struggle
for survival. Darwin came very near to this conception of
definite variability when he pointed out that 'if a country
were changing the altered conditions would tend to cause
variation, not but what I believe most beings vary at all
times enough for selection to act on.' Extermination would
expose the remainder to 'the mutual action of a different
set of inhabitants, which I believe to be more important to
the life of each being than mere climate,' * and as 'the same
spot will support more life if occupied by very diverse
forms,' it is evident that selection will favour very great
diversity of structure.

"Bearing in mind this cumulative action of selection it
will follow that under constant or relatively constant con-
ditions the struggle for successful living will become more
and more selective in character, even if the actual number
of inhabitants remain more or less the same as when the
struggle first commenced. The selection of variations will
thus tend to pass through certain more or less ill-defined,
but nevertheless, real stages. In proportion as the struggle
becomes intense, either from the number or from the in-

*From Poulton's "Charles Darwin and the Theory of Natural
Selection" (Abstract of Darwin's letter to Professor Asa Gray).



i 5 6 DARWINISM TO-DAY.

creasing adaptability of the organisms, or both, certain
major essential adaptations, which were necessary for the
climatic and other more or less comparatively simple con-
ditions, will be supplemented by minor auxiliary variations
which in the earlier stages would not have appeared. And
still later, as more and more rigorous conditions of life were
imposed, the advantage would tend to rest with those organ-
isms which possessed highly coordinated adaptations, since
this would entail more rapid responsiveness to environment.
"As evolution advances from the unspecialised to the spe-
cialised, and higher and higher forms of life come into
being, with increasing complexity and specialisation of parts
entailing an increasingly delicate adjustment of those parts
to each other's needs, the relation of each part to the whole
organism becomes of more and more importance, and it
follows that selection must become more and more general-
ised in its action. No single variation could be of service
to any of the higher forms of life unless it was in more or
less complete harmony with the whole tendency of the
individual. The adjustment of parts and their mutual inter-
dependence make it essential for adaptation that the relation
of parts be preserved; consequently, correlated minute
favourable variations will tend to be more and more selected
as evolution passes from the unspecialised to the specialised
forms of life. This response of the whole organism should
be still more delicate in those forms of life that are con-
tinually subjecting themselves to changed conditions; hence
this delicacy of adjustment is far more necessary in the
higher forms of animal life than in the more stationary plant
organisms, and in the developing nervous system of animals
we have just the central adjusting system that is required for
these conditions. With evolution of type there will thus be
an increasingly definite tendency given to organic, espe-
cially the animal, forms of life, if the acting principle of
evolution has been selectional. Selection is, therefore, able



DARWINISM DEFENDED. 157

to account for the steadily progressive tendency of life as a
whole without calling to its aid any unknown and doubtful
perfecting principle.

"To summarise : Natural selection, acting on the whole
organism, tends to produce more and more definite tend-
encies in all surviving forms of life, which tendencies are
progressive and continuous in character. Variable condi-
tions, by partially altering the line of selection, induce a
temporary indefmiteness. And lastly, the process of selec-
tion being itself able to be the indirect, though not the direct,
cause of those favourable variations, which it subsequently
selects from, is able to dispense with any subsidiary factors,
provided it has a certain number of elementary properties
of life which afford sufficient material to work with."



APPENDIX.

1 Semper, Carl, "Der Haeckelismus in der Zoologie," 1876.

* In 1876, Gustav Jaeger anticipated Weismann's later much-
heralded theory of the continuity of the germ-plasm in his
"Zoologische Briefen."

* For an excellent detailed critical account of these general, as
well as the several accessory theories (amphimixis, polar bodies,
etc.) of Weismann, see Romanes's "An Examination of Weismann-
ism," 1893.

* It is of interest to note that the strongest defenders of neo-
Darwinism to-day are the English naturalists. Americans mostly
lean toward neo-Lamarckism ; the Germans are divided.

6 Plate, Ludwig, "Uber die Bedeutung des Darwin'schen Selec-
tionsprinzip und Probleme der Artbildung," 2d ed., 1903.

6 Prof. Weldon, an English Darwinian, has recorded (Nature,
Sept. 22, 1898) an extremely interesting and much discussed statis-
tical and experimental study of the presumable action of natural
selection working on slight fluctuating quantitative variations. "I
can only attempt to discuss," says Prof. Weldon, "the importance
of small variations, and the rate of organic change, in the one case
which I happen to know. The particular case I have myself studied
is the variation in the frontal breadth of Carcinus mcenas [a small
.shore-crab].



I5 8 DARWINISM TO-DAY.

"During the last six years my friend, Mr. Herbert Thompson, and

I have studied in some detail the state of this character in the

Weldon'sex- sma11 shore-crabs which swarm on the beach below

periments on " the laboratory of the Marine Biological Association,

Oaroinus. a t Plymouth.

"I will show you that in those crabs small changes in the size of
the frontal breadth do, under certain circumstances, affect the death-
rate, and that the mean frontal breadth among this race of crabs is,
in fact, changing at a rate sufficiently rapid for all the require-
ments of a theory of evolution.

"In Table IV [omitted], you see three determinations of the
mean frontal breadth of these crabs, expressed in terms of the
carapace-length, taken as 1,000. You see that the mean breadth
varies very rapidly with the length of the crab, so that it was neces-
sary to determine it separately in small groups of crabs, such that
the length of no two crabs in a group differed by more than a
fifth of a millimetre. The first column of the table shows you the
mean frontal breadth of twenty-five such groups, between 10 and 15
millimetres long, collected in 1893. These crabs were measured by
Mr. Thompson. The second column shows you the mean frontal
breadth in twenty-five similar groups of crabs, collected in 1895, and
also measured by Mr. Thompson. You see that in every case the
mean breadth in a group of crabs collected in 1895 is less than it
was in crabs of the same size collected in 1893. The third column
contains the result, so far as it is yet obtained, of my own measure-
ment of crabs collected this year. It is very incomplete, because
the 1895 crabs were collected in August and September, and I was
anxious to compare them with crabs collected this year at the same
season, so that there has not yet been time to measure the whole
series. The measurements are sufficient, however, to show that
the same kind of change has taken place during the last three
years as that observed by Mr. Thompson in the interval between
1893 and 1895. Making every allowance for the smallness of the
numbers so far measured this year, there is no doubt whatever that
the mean frontal breadth of crabs from this piece of shore is
considerably less now then it was in 1895 among crabs of the
same size.*

"These results all relate to male crabs. The change in female

*I shall, of course, consider it my duty to justify this statement
by more extensive measurement as soon as possible. In the mean-
time I may say that I have measured other small groups of crabs,
male and female, from the same place, at different seasons of the
years 1896-98, and the results agree with those recorded in the
table.



DARWINISM DEFENDED. 159

crabs during this time has been less than the change in male crabs,
but it is, so far as my measurements at present permit me to speak,,
going on in the same direction as the change in male crabs.

"I think there can be no doubt, therefore, that the frontal breadth,
of these crabs is diminishing year by year at a rate which is very-
rapid, compared with the rate at which animal evolution is com-
monly supposed to progress.

"I will ask your patience for a little while longer, that I majr
tdll you why 1 feel confident that this change is due to a selective
destruction, caused by certain rapidly changing conditions of
Plymouth Sound.

"On either side of Plymouth itself a considerable estuary opens
into the Sound, and each of these estuaries brings down water
from the high granite moorlands, where there are rich deposits of
china clay. Those of you who know Dartmoor will remember that
in rainy weather a great deal of china clay is washed into the
brooks and rivers, so that the water frequently looks white and.
opaque, like milk. Much of this finely divided china clay is carried
down to the sea ; and one effect of the breakwater has been to
increase the quantity of this fine silt which settles in the Sound
itself, instead of being swept out by the scour of the tide and the
waves of severe storms.

"So that the quantity of fine mud on the shores and on the bot-
tom of the Sound is greater than it used to be, and is constantly
increasing.

"But this is not all. During the forty or fifty years which have
gone by since the breakwater was completed, the towns on the
shores have largely increased their population ; the great dockyard
at Devonport has increased in size and activity; and the ships
which visit the Sound are larger and more numerous than they
were. Now the sewage and other refuse from these great and
growing towns and dockyards, and from all these ships, is thrown
into the Sound ; so that while it is more difficult than it used to be
for fine silt to be washed out of the Sound, the quantity thrown into
it is much greater than it was, and is becoming greater every day.

"It is well known that these changes in the physical conditions
of the Sound have been accompanied by the disappearance of ani-
mals which used to live in it, but which are now found only outside
the area affected by the breakwater.

"These considerations induced me to try the experiment of keeping
crabs in water containing fine mud in suspension, in order to see
whether a selective destruction occurred under these circumstances
or not. For this purpose, crabs were collected and placed in a large
vessel of sea-water, in which a considerable quantity of very fine



x6o DARWINISM TO-DAY.

china clay was suspended. The clay was prevented from settling
by a slowly moving automatic agitator; and the crabs were kept
under these conditions for various periods of time. At the end
of each experiment the dead were separated from the living, and
both were measured.

"In every case in which this experiment was performed with
china clay as fine as that brought down by the rivers, or nearly so,
the crabs which died were on the whole distinctly broader than
the crabs which lived through the experiment, so that a crab's
chance of survival could be measured by its frontal breadth.

"When the experiment was performed with coarser clay than
this, the death-rate was smaller, and was not selective.

"I will rapidly show you the results of one or two experiments.
The diagram [omitted] shows the distribution of frontal breadths,
about the average proper to their length, in 248 male crabs treated
in one experiment. Of these crabs, 154 died during the experiment,
and 94 survived. The distribution of frontal breadths in the sur-
vivors is shown by the lower curve in the diagram, and you see
that the mean of the survivors is clearly below the mean of the
original series, the mean of the dead being above the original mean.
"Two other cases, which are only examples of a series in my
possession, show precisely the same thing.

"These experiments seemed to me to show that very finely divided
china clay does kill crabs in such a way that those in which the
frontal breadth is greatest die first, those in which it is less live
longer. The destruction is selective, and tends to lower the mean
frontal breadth of the crabs subjected to its action. It seemed to
me that the finer the particles used in the experiments, that is to
say, the more nearly they approached the fineness of the actual silt
on the beach, the more selective their action was.

"I, therefore, went down to the beach, where the crabs live, and
looked at the silt there. This beach is made of moderately small
pieces of mountain limestone, which are angular and little worn
by water. The pieces of limestone are covered at low tide with
a thin layer of very fine mud, which is much finer than the china
clay I had used in my experiments, and remains suspended in
still water for some time. Under these stones the crabs live, and
the least disturbance of these stones raises a cloud of very fine
mud in the pools of water under them. By washing the stones of
the beach in a bucket of sea-water, I collected a quantity of this
very fine mud, and used it in a fresh series of experiments, precisely
as I had before used china clay, and I obtained the same result.
The mean frontal breadth of the survivors was always smaller
than the mean frontal breadth of the dead.



DARWINISM DEFENDED. 161

"I think, therefore, that Mr. Thompson's work, and my own,
have demonstrated two facts about these crabs; the first is that
their mean frontal breadth is diminishing year by year at a measur-
able rate, which is more rapid in males than in females; the second
is that this diminution in the frontal breadth occurs in the presence
of a material, namely, fine mud, which is increasing in amount,
and which can be shown experimentally to destroy broad-fronted
crabs at a greater rate than crabs with narrower frontal margins.

"I see no shadow of reason for refusing to believe that the action
of mud upon the beach is the same as that in an experimental
aquarium; and if we believe this, I see no escape from the con-
clusion that we have here a case of Natural Selection acting with
great rapidity, because of the rapidity with which the conditions
of life are changing."

These observations and conclusions of Professor Weldon have
been the subject of much discussion. The adverse criticism has, on
the whole, seemed to be successful in discrediting the case as an
example of any such clear-cut action of natural selection, as Weldon
seems to hold it to be. J. T. Cunningham (Natural Science, Vol.
XIV, pp. 38-45, 1899) concludes, after a critical analysis of the
work, that "Weldon's observations may be completely explained by
variations in the amount or rate of growth. The difference in
different years would be at once explained if the amount of change
in frontal breadth was constant for each moult, while the amount
of growth was variable. The fact is, that in 1893 crabs of a given
frontal breadth were larger than in 1895 and 1898; and I have
shown that the summer of 1893 was exceptionally fine and warm.
Either the warmth alone, or warmth and food together, very prob-
ably made the crabs grow more in that year for the same number
of moults. On this view the broad-fronted crabs died in the expe-
riments with clay and mud because they were younger and weaker.
In the same way the crabs that moulted in the bottles possibly
grew more than those in the sea, because they were kept in warmer
water and supplied with more food. Therefore they were, after
the moult, larger than those in the sea of the same relative frontal
breadth.

"The change described is not, if terms are used correctly, a change
in the character of the species, but merely a change in the rate of
development. The variations investigated are not individual differ-
ences, since each individual in the course of its growth passes
through each one of the variations in -its own person. It has not
been shown that the change has gone on continuously for five
years, or that it has taken place only in waters where there is much
mud. If tadpoles of the same size were found to have shorter tails



j6z DARWINISM TO-DAY.

in one year than in another, few biologists would draw the con-
clusion that the result was due to the selective destruction of those
with the longest tails. The more probable explanation would be
that those with the shorter tails were in a more advanced stage
of their metamorphosis."
T Plate, L., "Uber die Bedeutung," etc., pp. 31-32, 1903-

Tayler, J. L., "The Scope of Natural Selection," Nat. Science,
Vol. XV, pp. 114-129, 1899.

* Morgan, C. Lloyd, "Factors in the Evolution of the Mammalia,"
Nat. Science, pp. 97-ioi, 1892.

10 Plate, L., "Uber die Bedeutung," etc., pp. 159-160, 1903.

11 Tayler, J. L., "The Scope of Natural Selection," Nat. Science,
Vol. XV, pp. 114-129, 1899. I quote as follows: "In the development

Ta ler's ex- * ^ e individual we see a disappearance of structures,
planation of de- which appear to become, with advancing development,
generation by useless, almost parallel to the gradual disappearance of
natural selection. ru dj ments> e t C-j j n the history of the species evolution.
And a common explanation for both of these series of phenomena
can, I believe, be satisfactorily found in the known facts of nutrition.
Growth of any tissue would seem to depend on three conditions,
a stimulus of the part adequate to promote functional activity,
a proper food supply, and efficient removal of products produced
by that particular tissue's activity. There is abundant evidence
to prove that a tissue tends to degenerate if its own excretory
products are not removed; the evil effects produced by fatigue
products in muscle and other tissues on the activity of the tissue
itself, prove that this factor must be of great importance where-
ever it is found to occur. Just as the growth and development of
bacteria are interfered with, and finally altogether checked by the
accumulation of products of their own activity, so a tissue in the
higher organisms has its activity impaired and its power lessened
when for some reason diminished elimination of its own metabolic
products occurs. Now both in the development of the individual
and the race we see an alteration of structure, a gradual transition
from the less to the more specialised, and in this gradual transition
there must be, as I endeavoured to prove in my answer to the last
objection, an alteration in the line of functional activity of the
parts, and that, owing to this fact, a tissue that was necessary in
the earlier stages became less and less so as specialisation advanced,
the whole tendency of the specialising organism being continually
and increasingly against the- earlier, less specialised, stages. It will
thus happen that every structure which is becoming useless, owing to
its deficient specialisation, whether in the history of the race or the
individual, will have two adverse sets of conditions to contend



DARWINISM DEFENDED. 163

with one, defective elimination of its own tissue products, owing
to its becoming increasingly removed from the growing organismal
specialisation of food products, while secondly, for this same reason,
its own food supply will become less and less suitable. This theory
would apply equally to germinal and somatic development and
atrophy of structure ; there would thus, through the alteration of
functional activity of the whole organism, be brought about elimina-
Jion of all structures not in the line of evolution; and, therefore,
organismal selection alone, if this theory is sound, would be able
to explain the complete disappearance of rudiments, the various
forms of development and atrophy, without calling to its aid climatic
inheritance, panmixia, and germinal or any other form of particular
selection."

13 See the account of the observations of Kellogg and Bell in the
appendix of chap. iv.

18 Morgan, C. Lloyd, "Animal Behaviour," p. 269.

14 De Vries, H., "Die Mutationstheorie," 2 vols., 1901, 1903.

16 Plate, in a later briefer treatment ("Darwinismus kontra Muta-
tionstheorie," Archiv f. Rassen- und Gesellschaft-Biologie, Vol. Ill,
Plat 'a exnla- PP* I 83~ 2O ) 1906) of some of the offered objections to
nation of charac- natural selection refers to this matter from a slightly



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 15 of 38)