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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 16 of 38)
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ter fixity in do- different angle. "So sehr der Ziichter danach streben
mestic animals. musS; er i,ii c h konstante Formen zu erhalten, um der
Miihe der bestandigen Auslese enthoben zu sein, so wenig spielt dieser
Punkt in der freien Natur eine Rolle. Hier findet eine nie nachlas-
sende Zuchtwahl statt, wodurch der betreffende Charakter auf einer
gewissen Hohe erhalten und vor Riickschlag bewahrt wird. Welcher
Grad von Konstanz nun auf diesem Wege im Laufe von Tau-
senden von Generationen erzielt werden kann, ist eine zurzeit
noch ungeloste Frage, die ihrer Natur nach wohl kaum mit Sicher-
heit beantwortet werden kann. Jedoch lehrt die Tier- und Pflanzen-
zucht, dass der Riickschlag nach dem Aufhoren der Selektion
um so spater und um so seltener eintritt, je langer und je intensiver
der Ziichtungsprozess vorher betrieben worden ist. Daraus ist zu
schliessen, dass die langandauernde Zuchtwahl, welche die Natur
ausiibt, jenen relativ hohen Grad von Erblichkeit zu erzeugen
vermag, welcher den Spezies-Charakteren im allgemeinen zukommt,
denn vollig konstant sind diese bekanntlich auch nicht."

" Tayler, J. L., "The Scope of Natural Selection," Nat. Science,
Vol. XV, p. 119 ff., 1899-



CHAPTER VII.

DARWINISM DEFENDED (CONTINUED) : PLATE'S
CONCILIATORY DEFENCE.

THE foregoing consideration of the answers of the Dar-
winians to the objections urged against the effectiveness of
the selection theory as an explanation of evolution makes
no pretence of having included, or even referred to, all
the arguments offered by the defenders, and it is only fair
to note that by no means all Darwinians and neo-Darwin-
ians agree to making the concessions listed in the early
part of the chapter. Some refuse a certain one or
two of these concessions, some another or others, some
indeed will make no admissions at all. With these last we
are past arguing. The discussion assumes too much an "it
is, it isn't" character to be particularly illuminating or pro-
gressive. But because of those who concede in considerable
measure, and deny in some measure, the validity of those
chief objections to the species-forming capacity of natural
selection, the general character of the ground on which
this last stand for the old flag is being made should at least
be indicated.

This half-surrendered but still not quite deserted position

is perhaps most clearly to be seen through the smoke of

Plate's con- battle by fixing one's eyes on the representative

object Jons to ^ figUre f Ludwi " Plate ' a stron g Darwinian,
selection. but one not blinded by prejudice or with ears

wilfully closed to the calls of reason. In his recent elaborate
discussion ' of Darwinism, so often already referred to and
quoted from in these present chapters, he groups under the
head of wesentliche Einwdnde (important objections) the

!6 4



DARWINISM DEFENDED. 165

attacks on the species-forming capacity of natural selection,
which are based on (i) the slightness and inutility of the
fluctuating Darwinian variations, and (2) the improbability
of the right variations appearing at the right time to make
possible the development of specialisations of qualitative
and coadaptive character. In a discussion of some length
pp. 32-77), mostly quite fair and unprejudiced, he brings
out the best and strongest arguments that the faithful Dar-
winians have to offer to reduce the force of at least, if not to
answer satisfactorily, even for themselves, the most effective
attacks on the capacity of selection. In very condensed form
I present in the following paragraphs the essential points
in these defensive arguments.

In regard to the first objection, namely, that the very
slight or small differences in organs and functions which
result from the fluctuating or Darwinian varia-
to'the Btightnen ^ ons cannot be sufficiently advantageous or
of Darwinian disadvantageous enough to afford "handles"
for natural selection, that is, cannot be of life-
and-death-determining value, Darwin devoted, in his "Origin
of Species," a whole chapter of discussion and argument
to show that in many cases even the slightest of differences
may conceivably (it is of course a matter practically incapa-
ble of proof by observation or experiment) be sufficient to
turn the scale, in a rigorous competition, one way or the
other. In many other cases such differences could not, even
to Darwin, appear sufficient to be of a life-and-death advan-
tage or disadvantage. But Darwin too often, Plate admits,
confounded mere usefulness * with life-and-death-deciding
usefulness (or non-usefulness).

However, for many cases Plate maintains that the slight
Darwinian variations can serve as handles for selection,
particularly in periods of unusual rigour of competition
or fierceness of struggle (either active or passive) : ex-
amples are, slight differences in the speed of preyed-on



166 DARWINISM TO-DAY.

animals when pursued by an enemy, or slight differences
in the length of neck of the giraffe in time of scarcity of
foliage, or slight differences in the effectiveness of the
organs of sense at times of approaching danger, or in
endurance of cold, heat, hunger, dryness, etc., or in
the clothing of hairs or feathers, the number of capil-
laries in the skin, or richness of glandular secretion, and
the like, in times of special stress of weather. "Dodel-
Port ' has shown that microscopically fine hairs are capable
of keeping plant-lice away from leaves or buds, and that
very slight differences in the specific gravity of the seeds
of water-plants may determine whether these seeds sink to
the bottom and consequently germinate or not. For the long
nights of migratory birds or for birds like our house-doves
which protect themselves from birds of prey by swift flights
upward to great heights, every smallest amount of advan-
tage in the pneumaticity of the bones will be of worth and
finally of vital advantage, just as every racing bicyclist
knows by experience that for his record-breaking at-
tempts he must have a machine in which every part is
made as light as possible, for the effects of weight are cumu-
lative in course of time." And Plate fills a couple of pages
with other similar cases. "Whoever scrutinises the life of
nature and of man with biologically trained eye sees over
and over again the coming of great effects from slight
causes. The average of accidents in factories increases in
proportion to the age of the workers, because muscular
strength and keenness of the sense organs decrease with
increasing age. In each age-class the difference is but
slight, but in spite of that it demands its sacrifice. Nageli,
in a paper concerning the abundance of tuberculosis, showed
that among 500 dead human bodies examined 97 per cent,
showed traces, at least, of tuberculosis. That is, practically
every adult human is tainted by this disease. Now how
often must slight differences in body structure, life habits,



DARWINISM DEFENDED. 167

hygienic conditions, yes, even in temperament, determine
whether there shall be healing or death? The iridescent
colours of many male birds, butterflies, and certain parasitic
copepods (Sappharina), are certainly of a nature to pro-
duce a great effect on the eye, but these colour effects are
not the result of special pigments but of microscopically
minute structural conditions. In Africa the tsetse-fly 4 ex-
tends over large regions, and only those cattle with a skin of
a certain thickness, so that the tiny proboscis of the fly
cannot penetrate it, can live in these regions immune from
the fatal attacks of the pest. Many poisons work in almost
infinitely weak dilution a 1-200,000 solution of ricin, for
example, is able to kill mice."

Plate presents a second type of answer to the objection
by calling on certain aids or auxiliary principles by whose in-
fluence a difference at first unimportantly small
may aid slight gradually comes to be transformed into one of
Taxations. selective value, or may reach this stage sud-
denly by means of a change in life habits. This may come
about "through correlation, 5 that is, through that unknown
law of growth by which an indifferent organ may be so
bound up with or related to a useful organ " that it, the
indifferent organ, is perfected along with the useful organ
as this latter is developed or specialised through selection.
All organs of an animal are intimately related to and influ-
enced by one another : each is in relation to the other just
as to the outer world. How close this inter-dependence is,
is most easily appreciated by one in his own case when sick :
a constipation causes headache, a slight diarrhoea affects the
composition of the urine, etc. The correlation can be so
intimate and important, as the case of the secondary sexual
characters shows, that its origin and development depends
directly on particular definite stages of the related organs."
In the case of many animals the appearance of various curi-
ous and large modifications of legs, wings, skin, feathers,



168 DARWINISM TO-DAY.

hair, etc., etc., depends on the various stages of development
reached by the reproductive organs. Now these secondary
organs or modifications thus produced through the influence
of other organs may be for a while slight and indifferent
in character, but yet safely maintained. When they reach
a stage of utility or of positive disadvantage they will then
be further perfected, or on the other hand be extinguished,
by selection.

The principle of the change of function (Functions-

wechsel) first elaborated by Dohrn, 7 is also called on by

Plate to play an important part in explaining

Donrn's prm- -111 i

ciple of change how an organ of considerable specialisation can
of function. ^ s j lown to h ave |, een developed by selection,
although the function it is now performing seems to be one
that could have been useful only in a perfected state and
hence could not have made the organ so constantly ad-
vantageous in all the slow and gradual stages of its evolution
as to be of selective value in its beginning stages. Dohrn's
principle is stated as follows : "An organ can, in its service
of a certain definite useful function, be developed by natural
selection to a certain stage. Simultaneously a second func-
tion (Functionserweiterung) can have developed, due to
some special peculiarity or condition of the position, struc-
ture, or capacity for movement, which may have a value in
another direction from that of the first function. Thus
the appendages of crabs serve often special functions in rela-
tion to respiration, copulation, and care of the eggs or
young, while their original locomotory function may still
be maintained or may be more and more surrendered in
favour of the new functions." Numerous other specific ex-
amples are obvious enough to any student of biology. Now
the new functions in many cases become the more import-
ant so that there in time results a complete change of func-
tion which wholly alters the physiological character of the
organ, and in many cases it is difficult to see (if one does



DARWINISM DEFENDED. 169.

not know the phyletic history of the organ and the
function) just how selection could have developed such an
organ by slow degrees from slight beginnings. But the
secret of the explanation, which is a perfectly consistent
Darwinian explanation, lies in the Functionswechsel phe-
nomenon.

"Indifferent characters can suddenly become of selective
value through change of environmental conditions or of
life-habits. The cranial sutures are certainly of no vital
importance with the reptiles and birds, but they can be of
very great importance to the viviparous mammals as adapta-
tions for passing the pelvis during birth. Lacerla vivipara
has, perhaps, no advantage through its viviparousness over
its nearly related species in our country, but in Scandinavia
it has to thank this peculiarity alone for its success m life,,
because the development of its young is rendered inde-
pendent of the sun by it. The nectaries were probably at
first useless to the flowers ; from that moment, however,
when the insects learned to know them as food reservoirs
and unwittingly insured cross-pollination by their visits to
them, they became of the greatest importance and the indi-
rect cause of the origin of the colour brilliance of the
flowers.

"There are organs of universal character which can be-
come modified in most widely differing directions. Thus
the tail of the mammals, originally a long, evenly-haired
organ, can, without going through any very elaborate
changes, be modified into a bushy steering-rudder of special
use in climbing from branch to branch ; or by the outgrowth
of a terminal tuft be changed into a flying fan ; or by the par-
tial loss of the hair become a grasping organ, or a balancing-
organ, or an aid in leaping, a rudder in swimming, or a cover
against rain and cold (Myrmecophaga jubata}. The append-
ages of crabs, the cirri of the annelids, and the teeth of mam-
mals are further examples of a similar plasticity and capacity



170 DARWINISM TO-DAY.

for modification in the most manifold ways, in which the
first stages are often of immediate use."

Following these suggestions as to the aid that selection
may have from various helping conditions to make its

starts, Plate discusses as further similarly help-
airfrom C ini m8 ^ conditions or auxiliary principles three most
herited results important matters, namely, the effects of con-

tinued use on parts, the principle of orthogen-



discontinuous es j S) an( j the tacts of sudden discontinuous
variation. But as these three categories of
biological phenomena and principles are exactly those,
among others, which anti-Darwinians hold to be not aids
to the selection theories, but to be the basis if not of actually
replacing or substitutionary theories, at least of precisely
those objections to the species-forming capacity of the strict
Darwinian factors which have necessitated some of the
principal concessions made by the Darwinists, it is obvious
that Plate's discussion of them is in itself simply the actual
making of the concessions already noted as having been
admitted by most Darwinians. Each of these categories
of phenomena and principles is of course of much import-
ance and interest, and they will all be found to be fairly fully
set out in the chapters following this one.

Plate's answers to the second important objection, namely,
that selection relies too much on chance and is therefore
Answ to improbable and inexact, may now be noted. He
the objection distinguishes two phases of this objection. The
rpStVrf first he expresses as follows : "It is highly im-
seiectionon probable that for the progressive development
or perfecting of an organ there will always
appear just at the needed time the variation necessary for
selection, that is, the exactly needed adaptive modification."
The second phase is: "It is highly improbable that in the
development of a complicated organ, or body-part, or in
the perfecting of a changing adaptation the numerous indis-



DARWINISM DEFENDED. 171

pensable modifications will appear in such a series that a
harmonious correlation of the single variations will be
possible."

Referring especially to the first phase of the general ob-
jection he says :

"Thus this doubting query is, why do there always appear
just the right variations at the right time? Or, somewhat
differently expressed, in the words of Cope,* 'since the
number of variations possible to the organism is very great,
the probability of the admirably adaptive structures which
characterise the latter having arisen by chance is extremely
small.'

"Whoever expresses such doubts unwittingly hitches the
wagon before the horse. Selection directs itself according
to the variation, not variation according to
selection. If the variability is large, selection



not variation has a large choice ; if the variability is small,
then there are but few lines of evolution open.
Experience teaches that in general, the variability of organ-
isms is very large, that it occurs both quantitatively and
qualitatively in such pronounced manner in all individuals
of a species that it can be readily recognised without re-
course to complex methods of investigation, and that ho
characteristic (size, form, colour, numerical relation, consti-
tutional vigour, instinct, life-habit) is free from it in any
life stage from egg to last drawing of the breath. It is
precisely to this variability expressing itself in the most
manifold ways and combinations that is to be ascribed the
condition that any individual as such is, usually, readily
to be distinguished from other individuals of the same
species. It results from this that the individual variation is
indeterminate and undirected, or better expressed, universal
and all sided, and that at any given moment the exactly
needed modification will always appear in a number of indi-
viduals of any species rich in individuals, provided that



172 DARWINISM TO-DAY.

the needed variation can be produced through a slight ad-
vance or progressive change. Naturally it is not sufficient
if the variation appears in only a few isolated individuals,
but it is necessary, for the modification of the species, that
this variation occur in so many individuals that it will not
be extinguished through interbreeding but on the contrary
will be perpetuated. In other words selection works, except
, in scattered cases where single or rare varia-

Selection works

with plural vari- tions are specially favoured by accidental iso-
lation, not with single but with plural variations
or varieties. Through this the host of variations is im-
mensely reduced as far as they come into consideration as
handles for selection, and of course only in this sense is
there any reason at all for the query as to whether we can
assume that the right variation will always be present at the
right time. The answer can only be, certainly not always :
many promising beginnings must always be checked in the
germ or at half-way, but in infinitely many cases the needed
plural variation will appear, because the same external
factors change a whole group of animals simultaneously
so that progress is possible. But, it goes without saying,
only a slow advance is conceivable on this basis.

"One must not, for the rest, forget that the same condi-
tion of selective worth may be reached simultaneously
through combinations of different peculiarities,

Same selective , ,

value may be and that the same effect may be attained by
various me ans, both of which facts render it
importantly easier to get this selective worth.
When pursued by an enemy one individual of the harassed
species may save itself by a quick leap, a second through
sharp ears, a third by sharp eyes. Wallace rightly explains
that the necessity for a giraffe in times of famine is only to
reach as high as possible in the trees, and that different
means may avail for this, as a longer neck, long legs, or a
long tongue, all of which may eventually come to be correl-



DARWINISM DEFENDED. 173

atively increased. The individuals which survive by these
aids may then later, through inter-crossing, exchange their
advantages and so lead to the production of a mean type
that shows a slight advance over earlier conditions in all
three organs. Mammals can protect themselves from flies
in various ways, either by a thick fur (bears), by reflexive
twitchings of the skin muscles (horse), by tails with tufted
ends (many hoofed animals), by a long neck which can bend
sideways so that the animal can reach any part of its body
as far as the hips (guanaco, stag) or finally by eyelids and
long movable ears, which restrain the flies from the easily
injured eyes. These means of protection from insects play
an important role in determining the habitus of many mam-
mals, and permit the conclusion that selection has been
instrumental in producing this habitus. Here, also, it is
possible for several of these means to be possessed at once
by the same animal, as in the case of the guanaco with its
long hair and elongate neck. It is absolutely necessary for
molluscs that live between tide-lines to have some means of
resisting the force of the surf. Many species possess this
means in their small size which allows them to crawl into
crevices and cracks in the rocks, but most of them have
developed a strong pedal sucker and a low roof-like uncoiled
shell which presses close to the rock surface and over which
the water flows without exerting any strong lateral pres-
sure. This is the case, for example, with Patella, Fissurella,
Chiton, Concholepas, Siphonaria, Gadinia, Calyptra, and
others. All three of these means of safety can come into
play simultaneously in selection, but it suffices when any
given individual possesses any one of these means in suffi-
cient degree of development.

"I shall note here several other examples which show
how related species reach the same advantage in the strug-
gle through different means, for we can assume from these
.facts that also the individuals of the same species often



I74 DARWINISM TO-DAY.

escape the same dangers in the struggle for existence by
means of different means. And by this the probability is
made greater that the 'needed variation' appears at the
right time. The differing characteristics of this sort will
later lead, through crossing, to the formation of a mixed
type, or, if the competition grows ever sharper with the
course of time, they will produce a separation of the species
into varieties (eventually species) with differing habits of
life, or finally they may meet in direct competition or strug-
gle with one another. The good flyers among the birds all
have long wings, but in some it is the fore arm which is
specially lengthened (cuckoo, goat-sucker, pigeon), in others
the hand (terns, humming-birds, eave swallows), and in
still others the upper arm (swan). While TaJ>irus ameri-
canus, like most mammals, drives the flies away from its
eyes by throwing down the eyelids, Tapirus indicus accom-
plishes the same thing by a strong rotation of the bulb of
the eye. Elephas africanus seizes very small objects with
its proboscis-fingers, while the Indian elephant lays the front
end of the trunk laterally on the ground, grasps the object
between the skin-folds, lifts it up high in this way, and
only then allows it to fall into the tip of the proboscis.
Poulton has shown by several examples that in cases of
mimicry the same effects may be got in very different ways.
The glass-like transparency of the wings, for example, is got
in the Heliconid genus Menthona by a considerable dimi-
nution in size of the scales, in the Danaid I tuna iliona through
the absence of most of the scales, in Castnia linus var. heli-
conoides, through the absence of pigment in the scales, which
are as large and numerous as usual, in the Pierid Dismor-
phia crise through the smallness of the scales, and finally in
the night moth Hyelosia heliconoides by the absence of pig-
ment and lessened number of the scales."

Plate next offers a detailed explanation on strict Darwin-
ian grounds of how such an extraordinary condition of



DARWINISM DEFENDED. 175

mimicry can be brought about as the famous case of Kal-
lima, the butterfly that simulates in colour, shape, and inti-
mate details of pattern such as veins, flecks,
fun S us spots, etc., a dead leaf with such fidelity
as to make it the wonder of every one who sees
it and the classic example of the possibilities of such protect-
ive resemblance. And he shows well that whatever diffi-
culties selection may have in its necessary dependence on.
the chance occurrence of the proper numerous and neces-
sarily simultaneously appearing variations to explain the
gradual development of such a specialisation, the only other
explanations so far offered are even more ludicrously de-
pendent on "luck." Piepers,' the most active and polem-
ically vigorous of all special opponents of the Darwinian
explanation of protective resemblance and mimicry, says :
"Chance alone can bring about such a correlation." As
Plate well says, "It is not without its comic aspect that a
violent antagonist of the selection theory should be found
clinging to the same safety-anchor 'chance,' that usually
is the constant reproach of the Darwinian. ... It would not
be difficult," continues Plate, "to refer to still other examples
to show that a needed selective value can often be attained
at the same time by the individuals of a species through
various means, by which the probability that this type of



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 16 of 38)