has sometimes been urged--viz. that we ought never to find inferior
forms of organization in company with superior, because in the struggle
for existence the latter ought to have exterminated the former. Or, to
quote the most recent expression of this view, "in every locality there
would only be one species, and that the most highly organized; and thus
a few superior races would partition the earth amongst them to the
entire exclusion of the innumerable varieties, species, genera, and
orders which now inhabit it[45]." Of course to this statement it would
be sufficient to enquire, On what would these few supremely organized
species subsist? Unless manna fell from heaven for their especial
benefit, it would appear that such forms could under no circumstances be
the most improved forms; in exterminating others on such a scale as
this, they would themselves be quickly, and very literally, improved off
the face of the earth. But even when the statement is not made in so
extravagant a form as this, it must necessarily be futile as an
objection unless it has first been shown that we know exactly all the
conditions of the complex struggle for existence between the higher and
lower forms in question. And this it is impossible that we ever can
know. The mere fact that one form has been changed in virtue of this
struggle must in many cases of itself determine a change in the
conditions of the struggle. Again, the other and closely allied forms
(and these furnish the best grounds for the objection) may also have
undergone defensive changes, although these may be less conspicuous to
our observation, or perhaps less suggestive of "improvement" to our
imperfect means of judging. Lastly, not to continue citing an endless
number of such considerations, there is the broad fact that it is only
to those cases where, for some reason or another, the lower forms have
not been exposed to a struggle of fatal intensity, that the objection
applies. But we know that in millions of other cases the lower (i. e.
less fitted) forms _have_ succumbed, and therefore I do not see that the
objection has any ground to stand upon. That there is a general tendency
for lower forms to yield their places to higher is shown by the gradual
advance of organization throughout geological time; for if _all_ the
inferior forms had survived, the earth could not have contained them,
unless she had been continually growing into something like the size of
Jupiter. And if it be asked why any of the inferior forms have survived,
the answer has already been given, as above.
[45] Syme, on the _Modification of Organisms_, p. 46.
There is only one other remark to be made in this connexion. Mr. Syme
chooses two cases as illustrations of the supposed difficulty. These are
sufficiently diverse--viz. Foraminifera and Man. Touching the former,
there is nothing that need be added to the general answer just given.
But with regard to the latter it must be observed that the dominion of
natural selection as between different races of mankind is greatly
restricted by the presence of rationality. Competition in the human
species is more concerned with wits and ideas than with nails and teeth;
and therefore the "struggle" between man and man is not so much for
actual _being_, as for _well-being_. Consequently, in regard to the
present objection, the human species furnishes the worst example that
could have been chosen.
* * * * *
Hitherto I have been considering objections which arise from
misapprehensions of Darwin's theory. I will now go on to consider a
logically sound objection, which nevertheless is equally futile,
because, although it does not depend on any misapprehension of the
theory, it is not itself supported by fact.
The objection is the same as that which we have already considered in
relation to the general theory of descent--namely, that similar organs
or structures are to be met with in widely different branches of the
tree of life. Now this would be an objection fatal to the theory of
natural selection, supposing these organs or structures in the cases
compared are not merely analogous, but also homologous. For it would be
incredible that in two totally different lines of descent one and the
same structure should have been built up independently by two parallel
series of variations, and that in these two lines of descent it should
always and independently have ministered to the same function. On the
other hand, there would be nothing against the theory of natural
selection in the fact that two structures, _not_ homologous, should come
by independent variation in two different lines of descent to be adapted
to perform the same function. For it belongs to the very essence of the
theory of natural selection that a useful function should be secured by
favourable variations of whatever structural material may happen to be
presented by different organic types. Flying, for instance, is a very
useful function, and it has been developed independently in at least
four different lines of descent--namely, the insects, reptiles, birds,
and mammals. Now if in all, or indeed in any, of these four cases the
wings had been developed on the same anatomical pattern, so as not only
to present the analogical resemblance which it is necessary that they
should present in order to discharge their common function of flying,
but likewise an homologous or structural resemblance, showing that they
had been formed on the same anatomical "plan,"--if such has been the
case, I say, the theory of natural selection would certainly be
destroyed.
Now it has been alleged by competent naturalists that there are several
such cases in organic nature. We have already noticed in a previous
chapter (pp. 58, 59), that Mr. Mivart has instanced the eye of the
cuttle-fish as not only analogous to, but also homologous with, the eye
of a true fish--that is to say, the eye of a mollusk with the eye of a
vertebrate. And he has also instanced the remarkable resemblance of a
shrew to a mouse--that is, of an insectivorous mammal to a rodent--not
to mention other cases. In the chapter alluded to these instances of
homology, alleged to occur in different branches of the tree of life,
were considered with reference to the process of organic evolution as a
fact: they are now being considered with reference to the agency of
natural selection as a method. And just as in the former case it was
shown, that if any such alleged instances could be proved, the proof
would be fatal to the general theory of organic evolution by physical
causes, so in the present case, if this could be proved, it would be
equally fatal to the more special theory of natural selection. But, as
we have before seen, no single case of this kind has ever been made
out; and, therefore, not only does this supposed objection fall to the
ground, but in so doing it furnishes an additional argument in favour of
natural selection. For in the earlier chapter just alluded to I showed
that this great and general fact of our nowhere being able to find two
homologous structures in different branches of the tree of life, was the
strongest possible testimony in favour of the theory of evolution. And,
by parity of reasoning, I now adduce it as equally strong evidence of
natural selection having been the cause of _adaptive_ structures,
independently developed in all the different lines of descent. For the
alternative is between adaptations having been caused by natural
selection or by supernatural design. Now, if adaptations were caused by
natural selection, we can very well understand why they should never be
homologous in different lines of descent, even in cases where they have
been brought to be so closely analogous as to have deceived so good a
naturalist as Mr. Mivart. Indeed, as I have already observed, so well
can we understand this, that any single instance to the contrary would
be sufficient to destroy the theory of natural selection _in toto_,
unless the structure be one of a very simple type. But on the other
hand, it is impossible to suggest any rational explanation why, if all
adaptations are due to supernatural design, such scrupulous care should
have been taken never to allow homologous adaptations to occur in
different divisions of the animal or vegetable kingdoms. Why, for
instance, should the eye of a cuttle-fish _not_ have been constructed on
the same ideal pattern as that of vertebrate? Or why, among the
thousands of vertebrated species, should no one of their eyes be
constructed on the ideal pattern that was devised for the cuttle-fish?
Of course it may be answered that perhaps there was some hidden reason
why the design should never have allowed an adaptation which it had
devised for one division of organic nature to appear in another--even in
cases where the new design necessitated the closest possible resemblance
in everything else, save in the matter of anatomical homology.
Undoubtedly such may have been the case--or rather such _must_ have been
the case--if the theory of special design is true. But where the
question is as to the truth of this theory, I think there can be no
doubt that its rival gains an enormous advantage by being able to
_explain_ why the facts are such as they are instead of being obliged to
take refuge in hypothetical possibilities of a confessedly
unsubstantiated and apparently unsubstantial kind.
Therefore, as far as this objection to the theory of natural selection
is concerned--or the allegation that homologous structures occur in
different divisions of organic nature--not only does it fall to the
ground, but positively becomes itself converted into one of the
strongest arguments in favour of the theory. As soon as the allegation
is found to be baseless, the very fact that it cannot be brought to bear
upon any one of all the millions of adaptive structures in organic
nature becomes a fact of vast significance on the opposite side.
* * * * *
The next difficulty to which I shall allude is that of explaining by the
theory of natural selection the preservation of the first beginnings of
structures which are then useless, though afterwards, when more fully
developed, they become useful. For it belongs to the very essence of the
theory of natural selection, that a structure must be supposed already
useful before it can come under the influence of natural selection:
therefore the theory seems incapable of explaining the origin and
conservation of _incipient_ organs, or organs which are not yet
sufficiently developed to be of any service to the organisms presenting
them.
This objection is one that has been advanced by all the critics of
Darwinism; but has been presented with most ability and force by the
Duke of Argyll. I will therefore state it in his words.
If the doctrine of evolution be true--that is to say, if all
organic creatures have been developed by ordinary generation from
parents--then it follows of necessity that the primaeval germs must
have contained potentially the whole succeeding series. Moreover,
if that series has been developed gradually and very slowly, it
follows, also as a matter of necessity, that every modification of
structure must have been functionless at first, when it began to
appear.... Things cannot be selected until they have first been
produced. Nor can any structure be selected by utility in the
struggle for existence until it has not only been produced, but has
been so far perfected as to actually be used.
The Duke proceeds to argue that all adaptive structures must therefore
originally have been due to special design: in the earlier stages of
their development they must all have been what he calls "prophetic
germs." Not yet themselves of any use, and therefore not yet capable of
being improved by natural selection, both in their origin and in the
first stages (at all events) of their development, they must be
regarded as intentionally preparatory to the various uses which they
subsequently acquire.
Now this argument, forcible as it appears at first sight, is really at
fault both in its premiss and in its conclusion. By which I mean that,
in the first place the premiss is not true, and, in the next place, that
even if it were, the conclusion would not necessarily follow. The
premiss is, "that every modification of structure must have been
functionless at first, when it began to appear;" and the conclusion is,
that, _qua_ functionless, such a modification cannot have been caused by
natural selection. I will consider these two points separately.
First as to the premiss, it is not true that every modification of
structure must necessarily be functionless when it first begins to
appear. There are two very good reasons why such should not be the case
in all instances, even if it should be the case in some. For, as a
matter of observable fact, a very large proportional number of incipient
organs are useful from the very moment of their inception. Take, for
example, what is perhaps the most wonderful instance of refined
mechanism in nature--the eye of a vertebrated animal. Comparative
anatomy and embryology combine to testify that this organ had its origin
in modifications of the endings of the ordinary nerves of the skin. Now
it is evident that from the very first any modification of a cutaneous
nerve whereby it was rendered able, in however small a degree, to be
differently affected by light and by darkness would be of benefit to the
creature presenting it; for the creature would thus be able to seek the
one and shun the other according to the requirements of its life. And
being thus useful from the very moment of its inception, it would
afterwards be gradually improved as variations of more and more utility
presented themselves, until not only would finer and finer degrees of
difference between light and shade become perceptible, but even the
outlines of solid bodies would begin to be appreciated. And so on, stage
by stage, till from an ordinary nerve-ending in the skin is evolved the
eye of an eagle.
Moreover, in this particular instance there is very good reason to
suppose that the modification of the cutaneous nerves in question began
by a progressive increase in their sensitiveness to temperature.
Wherever dark pigment happened to be deposited in the skin--and we know
that in all animals it is apt to be deposited in points and patches, as
it were by accident, or without any "prophecy" as to future uses,--the
cutaneous nerves in its vicinity would be better able to appreciate the
difference between sun and shade in respect of temperature, even though
as yet there were no change at all in these cutaneous nerves tending to
make them responsive to light. Now it is easy to see how, from such a
purely accidental beginning, natural selection would have had from the
first sufficient material to act upon. It being of advantage to a lowly
creature that it should distinguish with more and more delicacy, or with
more and more rapidity, between light and darkness by means of its
thermal sensations, the pigment spots in the skin would be rendered
permanent by natural selection, while the nerves in that region would by
the same agency be rendered more and more specialized as organs adapted
to perceive changes of temperature, until from the stage of responding
to the thermal rays of the non-luminous spectrum alone, they become
capable of responding also to luminous.
So much, then, for the first consideration which serves to invalidate
the Duke's premiss. The second consideration is, that very often an
organ which began by being useful for the performance of one function,
after having been fully developed for the performance of that function,
finds itself, so to speak, accidentally fitted to the performance of
some other and even more important function, which it thereupon begins
to discharge, and so to undergo a new course of adaptive development. In
such cases, and so far as the new function is concerned, the difficulty
touching the first inception of an organ does not apply; for here the
organ has already been built up by natural selection for one purpose,
before it begins to discharge the other. As an example of such a case we
may take the lung of an air-breathing animal. Originally the lung was a
swim-bladder, or float, and as such it was of use to the aquatic
ancestors of terrestrial animals. But as these ancestors gradually
became more and more amphibious in their habits, the swim-bladder began
more and more to discharge the function of a lung, and so to take a
wholly new point of departure as regards its developmental history. But
clearly there is here no difficulty with regard to the inception of its
new function, because the organ was already well developed for one
purpose before it began to serve another. Or, to take only one
additional example, there are few structures in the animal kingdom so
remarkable in respect of adaptation as is the wing of a bird or a bat;
and at first sight it might well appear that a wing could be of no
conceivable use until it had already acquired enormous proportional
dimensions, as well as an immense amount of special elaboration as to
its general form, size of muscle, amount of blood-supply, and so on.
For, obviously, not until it had attained all these things could it even
begin to raise the animal in the air. But observe how fallacious is this
argument. Although it is perfectly true that a wing could be of no use
_as a wing_ until sufficiently developed to serve the purpose of flight,
this is merely to say that until it has become a wing it is no use as a
wing. It does not, however, follow that on this account it was of no
prior use for any other purpose. The first modifications of the
fore-limb which ended in its becoming an organ of flight may very well
have been due to adapting it as an organ for increased rapidity of
locomotion of other kinds--whether on land as in the case of its now
degenerated form in the ostrich, or in water as in the case of the
expanded fins of fish. Indeed, we may see the actual process of
transition from the one function to the other in the case of
"flying-fish." Here the progressive expansion of the pectoral fins must
certainly have been always of use for continuously promoting rapidity of
locomotion through water; and thus natural selection may have
continuously increased their development until they now begin to serve
also as wings for carrying the animal a short distance through air.
Again, in the case of the so-called flying squirrels we find the limbs
united to the body by means of large extensions of the skin, so-that
when jumping from one tree to another the animal is able to sustain
itself through a long distance in the air by merely spreading out its
limbs, and thus allowing the skin-extensions to act after the manner of
a parachute. Here, of course, we have not yet got a wing, any more than
we have in the case of the flying-fish; but we have the foundations laid
for the possible development of a future wing, upon a somewhat similar
plan as that which has been so wonderfully perfected in the case of
bats. And through all the stages of progressive expansion which the skin
of the squirrel has undergone, the expansion has been of use, even
though it has not yet so much as begun to acquire the distinctive
functions of a wing. Here, then, there is obviously nothing "prophetic"
in the matter, any more than there was in the case of the swim-bladder
and the lung, or in that of the nerve-ending and the eye. In short, it
is the business of natural selection to secure the highest available
degree of adaptation for the time being; and, in doing this, it not
unfrequently happens that an extreme development of a structure in one
direction (produced by natural selection for the sake of better and
better adapting the structure to perform some particular function) ends
by beginning to adapt it to the performance of some other function. And,
whenever this happens to be the case, natural selection forthwith begins
to act upon the structure, so to speak, from a new point of departure.
So much, then, for the Duke's premiss--namely, that "every modification
of structure _must_ have been functionless _at first_, when it began to
appear." This premiss is clearly opposed to observable fact. But now,
the second position is that, even if this were not so, the Duke's
conclusion would not follow. This conclusion, it will be remembered, is,
that if incipient structures are useless, it necessarily follows that
natural selection can have had no part whatever in their inception. Now,
this is a conclusion which does not "necessarily" follow. Even if it be
granted that there are structures which in their first beginnings are
not of any use at all for any purpose, it is still possible that they
may owe their origin to natural selection--not indeed directly, but
indirectly. This possibility arises from the occurrence in nature of a
principle which has been called the Correlation of Growth.
Mr. Darwin, who has paid more attention to this matter than any other
writer, has shown, in considerable detail, that all the parts of any
given organism are so intimately bound together, or so mutually
dependent upon each other, that when one part is caused to change by
means of natural selection, some other parts are very likely to undergo
modification as a consequence. For example, there are several kinds of
domesticated pigeons and fowls, which grow peculiar wing-like feathers
on the feet. These are quite unlike all the other feathers in the
animal, except those of the wing, to which they bear a very remarkable
resemblance. Mr. Darwin records the case of a bantam where these
wing-like feathers were nine inches in length, and I have myself seen a
pigeon where they reproduced upon the feet a close imitation of the
different kinds of feathers which occupy homologous positions in the
wing--primaries, secondaries, and tertiaries all being distinctly
repeated in their proper anatomical relations. Furthermore, in this
case, as in most cases where such wing-feathers occur upon the feet, the
third and fourth toes were partly united by skin; and, as is well known,
in the wing of a bird the third and fourth digits are completely united
by skin; "so that in feather-footed pigeons, not only does the exterior
surface support a row of long feathers, like wing-feathers [which, as
just stated, may in some cases be obviously differentiated into
primaries, secondaries and tertiaries], but the very same digits which
in the wing are completely united by skin become partially united by
skin in the feet; and thus by the law of correlated variation of
homologous parts, we can understand the curious connexion of feathered
legs and membrane between the two outer toes[46]." The illustration is
drawn from the specimen to which I have referred.
[46] _Variation of Plants and Animals_, vol. ii. p. 315.
[Illustration: FIG. 117.--Feather-footed pigeon. Drawn from nature.]
Many similar instances of the same law are to be met with throughout
organic nature; and it is evident that in this principle we find a
conceivable explanation of the origin of such adaptive structures as
could not have been originated by natural selection acting directly upon
themselves: they may have been originated by natural selection
developing other adaptive structures elsewhere in the organism, the
gradual evolution of which has entailed the production of these by
correlation of growth. And, if so, when once started in this way, these
structures, because thus accidentally useful, will now themselves come
under the _direct_ action of natural selection, and so have their
further evolution determined with or without the correlated association
which first led to their inception.
Of course it must be understood that in thus applying the principle of
correlated growth, to explain the origin of adaptive structures where it
is impossible to explain such origin by natural selection having from
the first acted directly upon these structures themselves, Darwinists
do not suppose that in all--or even in most--cases of correlated growth
the correlated structures are of use. On the contrary, it is well known
that structures due to correlated growth are, as a rule, useless. Being
only the by-products of adaptive changes going on elsewhere, in any
given case the chances are against these correlated effects being
themselves of any utilitarian significance; and, therefore, as a matter
of fact, correlated growths appear to be usually meaningless from the
point of view of adaptation. Still, on the doctrine of chances, it is
to be expected that sometimes a change of structure which has thus been
indirectly produced by correlation of growth might happen to prove
useful for some purpose or another; and in as many cases as such
indirectly produced structures do prove useful, they will straightway
begin to be improved by the direct action of natural selection. In all
such cases, therefore, we should have an explanation of the _origin_ of
such a structure, which is the only point that we are now considering.
I think, then, that all this effectually disposes of the doctrine of
"prophetic germs." But, before leaving the subject, I should like to
make one further statement of greater generality than any which I have
hitherto advanced. This statement is, that we must remember how large a
stock of meaningless structures are always being produced in the course
of specific transmutations, not only by correlation of growth, which we
have just been considering, but also by the direct action of external
conditions, together with the constant play of all the many and complex
forces internal to organisms themselves. In other words, important as
the principle of correlation undoubtedly is, we must remember that even
this is very far from being the only principle which is concerned in the
origination of structures that may or may not chance to be useful.
Therefore, it is not only natural selection when operating indirectly
through the correlation of growth that is competent to produce new
structures without reference to utility. In all the complex action and
reaction of internal and external forces, new variations are perpetually
arising without any reference to utility, either present or future.
Among all this multitude of promiscuous variations, the chances must be
that some percentage will prove of some service, either from the first
moment of their appearance, or else after they have undergone some
amount of development. Such development prior to utility may be due,
either to correlation of growth, to the structure having previously
performed some other function, as already explained, or else to a
continued operation of the causes which were concerned in the first
appearance of originally useless characters. In a series of chapters
which will be devoted to the whole question of utility in the next
volume, I shall hope to give very good reasons for concluding that
useless characters are not only of highly frequent occurrence, but are
due to a variety of other causes besides correlation of growth. And, if
so, the possibility of originally useless characters happening in some
cases to become, by increased development, useful characters, is
correspondingly increased. Among a hundred varietal or specific
characters which are directly produced in as many different species by a
change of climate, for example, some five or six may be _potentially_
useful: that is to say, characters thus adventitiously produced in an
incipient form may only require to be further developed by a continuance
of the same causes as first originated them, in order that some
percentage of the whole number shall become of some degree of use. Those
professed followers of Darwin, therefore, who without any reason--or, as
it appears to me, against all reason--deny the possibility of useless
specific characters in any case or in any degree (unless correlated with
useful characters), are playing into the hands of Darwin's critics by
indirectly countenancing the difficulty which we are now considering.
For, if correlation of growth is unreasonably supposed to be the only
possible cause of the origin of incipient structures which are not
useful from the first moment of their inception, clearly the field is
greatly narrowed as regards the occurrence of incipient characters
sufficient in amount--and, still more, in constancy of appearance and
persistency of transmission--to admit of furnishing material for the
working of natural selection. But in the measure that incipient
characters--whether varietal or specific--are recognised as not always
or "necessarily" useful from the moment of their inception, and yet
capable of being developed to a certain extent by the causes which first
led to their occurrence, in that measure is this line of criticism
closed. For of all the variations which thus occur, it is only those
which afterwards prove of any use that are laid hold upon and wrought up
by natural selection into adaptive structures, or working organs. And,
therefore, what we see in organic nature is the net outcome of the
development of all the happy chances. So it comes that the appearance
presented by organic nature as a whole is that of a continual fulfilment
of structural prophecies, when, in point of fact, if we had a similar
record of all the other variations it would be seen that possibly not
one such prophecy in a thousand is ever destined to be fulfilled.
* * * * *
Here, then, I feel justified in finally taking leave of the difficulty
from the uselessness of incipient organs, as this difficulty has been
presented, in varying degrees of emphasis, by the Duke of Argyll, Mr.
Mivart, Professors Naegeli, Bronn, Broca, Eimer, and, indeed, by all
other writers who have hitherto advanced it. For, as thus presented, I
think I have shown that it admits of being adequately met. But now, I
must confess, to me individually it does appear that behind this
erroneous presentation of the difficulty there lies another question,
which is deserving of much more serious attention. For although it
admits of being easily shown--as I have just shown--that the difficulty
as ordinarily presented fails on account of its extravagance, the
question remains whether, if stated with more moderation, a real
difficulty might not be found to remain.
My quarrel with the conclusion, like my quarrel with the premiss, is due
to its universality. By saying in the premiss that _all_ incipient
organs are _necessarily_ useless at the time of their inception, these
writers admit of being controverted by fact; and by saying in the
conclusion that, _if_ all incipient organs are useless, it necessarily
follows that in _no_ case can natural selection have been the cause of
building up an organ until it becomes useful, they admit of being
controverted by logic. For, even if the premiss were true in
fact--namely, that all incipient organs are useless at the time of their
inception,--it would not necessarily follow that in no case could
natural selection build up a useless structure into a useful one;
because, although it is true that in no case can natural selection do
this by acting on a useless structure _directly_, it may do so by acting
on the useless structure _indirectly_, through its direct action on some
other part of the organism with which the useless structure happens to
be correlated. Moreover, as I believe, and will subsequently endeavour
to prove, there is abundant evidence to show that incipient characters
are often developed to a large extent by causes other than natural
selection (or apart from any reference to utility), with the result that
some of them thus happen to become of use, when, of course, the supposed
difficulty is at an end.
But although it is thus easy to dispose of both the propositions in
question, on account of their universality, stated more carefully they
would require, as I have said, more careful consideration. Thus, if it
had been said that some incipient organs are _presumably_ useless at the
time of their inception, and that in _some of these cases_ it is
difficult, or impossible, to conceive how the principle of correlation,
or any other principle hitherto suggested, can apply--then the question
would have been raised from the sphere of logical discussion to that of
biological fact. And the new question thus raised would have to be
debated, no longer on the ground of general or abstract principles, but
on that of special or concrete cases. Now until within the last year or
two it has not been easy to find such a special or concrete case--that
is to say, a case which can be pointed to as apparently excluding the
possibility of natural selection having had anything to do with the
genesis of an unquestionably adaptive structure. But eventually such a
case has arisen, and the Duke of Argyll has not been slow in perceiving
its importance. This case is the electric organ in the tail of the
skate. No sooner had Professor Cossar Ewart published an abstract of his
first paper on this subject, than the Duke seized upon it as a case for
which, as he said, he had long been waiting--namely, the case of an
_adaptive_ organ the genesis of which _could not possibly_ be attributed
to natural selection, and must therefore be attributed to supernatural
design. Now, I do not deny that he is here in possession of an admirable
case--a case, indeed, so admirable that it almost seems to have been
specially designed for the discomfiture of Darwinians. Therefore, in
order to do it full justice, I will show that it is even more formidable
than the Duke of Argyll has represented.
Electric organs are known to occur in several widely different kinds of
fish--such as the _Gymnotus_ and _Torpedo_. Wherever these organs do
occur, they perform the function of electric batteries in storing and
discharging electricity in the form of more or less powerful shocks.
Here, then, we have a function which is of obvious use to the fish for
purposes both of offence and defence. These organs are everywhere
composed of a transformation of muscular, together with an enormous
development of nervous tissue; but inasmuch as they occupy different
positions, and are also in other respects dissimilar in the different
zoological groups of fishes where they occur, no difficulty can be
alleged as to these analogous organs being likewise homologous in
different divisions of the aquatic vertebrata.
Now, in the particular case of the skate, the organ is situated in the
tail, where it is of a spindle-like form, measuring, in a large fish,
about two feet in length by about an inch in diameter at the middle of
the spindle. Although its structure is throughout as complex and perfect
as that of the electric organ in _Gymnotus_ or _Torpedo_, its smaller
size does not admit of its generating a sufficient amount of
electricity to yield a discharge that can be felt by the hand.
Nevertheless, that it does discharge under suitable stimulation has been
proved by Professor Burdon Sanderson by means of a telephone; for he
found that every time he stimulated the animal its electrical discharge
was rendered audible by the telephone. Here, then, the difficulty
arises. For of what conceivable use is such an organ to its possessor?
We can scarcely suppose that any aquatic animal is more sensitive to
electric shocks than is the human hand; and even if such were the case,
a discharge of so feeble a kind taking place in water would be
short-circuited in the immediate vicinity of the skate itself. So there
can be no doubt that such weak discharges as the skate is able to
deliver must be wholly imperceptible alike to prey and to enemies. Yet
for the delivery of such discharges there is provided an organ of such
high peculiarity and huge complexity, that, regarded as a piece of
living mechanism, it deserves to rank as at once the most extremely
specialized and the most highly elaborated structure in the whole animal
kingdom. Thousands of separately formed elements are ranged in row after
row, all electrically insulated one from another, and packed away into
the smallest possible space, with the obvious end, or purpose, of
conspiring together for the simultaneous delivery of an electric shock.
Nevertheless, the shock when delivered is, as we have just seen, too
slight to be of any conceivable use to the skate. Therefore it appears
impossible to suggest how this astonishing structure--much more
astonishing, in my opinion, than the human eye or the human hand--can
ever have been begun, or afterwards developed, by means of natural
selection. For if it be not even yet of any conceivable use to its
possessor, clearly thus far survival of the fittest can have had nothing
to do with its formation. On the other hand, seeing that electric organs
when of larger size, as in the _Gymnotus_ and _Torpedo_, are of obvious
use to their possessors, the facts of the case, so far as the skate is
concerned, assuredly do appear to sanction the doctrine of "prophetic
germs." The organ in the skate seems to be on its way towards becoming
such an organ as we meet with in these other animals; and, therefore,
unless we can show that it is now, and in all previous stages of its
evolution has throughout been, of use to the skate, the facts do present
a serious difficulty to the theory of natural selection, while they
readily lend themselves to the interpretation of a disposing or
fore-ordaining mind, which knows how to construct an electric battery by
thus transforming muscular tissue into electric tissue, and is now
actually in process of constructing such an apparatus for the
prospective benefit of future creatures.
Should it be suggested that possibly the electric organ of the skate may
be in process of degeneration, and therefore that it is now the
practically functionless remnant of an organ which in the ancestors of
the skate was of larger size and functional use--against so obvious a
suggestion there lie the whole results of Professor Ewart's
investigations, which go to indicate that the organ is here not in a
stage of degeneration, but of evolution. For instance, in _Raia
radiata_, it does not begin to be formed out of the muscular tissue
until some time after the animal has left the egg-capsule, and assumed
all the normal proportions (though not yet the size) of the adult
creature. The organ, therefore, is one of the very latest to appear in
the ontogeny of _R. radiata_; and, moreover, it does not attain its full
_development_ (i. e. not merely _growth_, but transforming of muscular
fibres into electrical elements) till the fish attains maturity. Read in
the light of embryology, these facts prove, (1) that the electric organ
of _R. radiata_ must be one of the very latest products of the
animal's phylogeny; and, (2) that as yet, at all events, it has not
begun to degenerate. But, if not, it must either be at a stand-still, or
it must be in course of further evolution; and, whichever of these
alternatives we adopt, the difficulty of accounting for its present
condition remains. In this connexion also it is worth while to remark
that the electric organ, even after it has attained its full
_development_, continues its _growth_ with the growth of the fish, and
this in a much higher ratio, either than the tail alone, or the whole
animal. Lastly, Prof. Burdon Sanderson finds that _section for section_
the organ in the skate is as efficient as it is in _Torpedo_. It is
evident that these facts also point to the skate's organ being in course
of phylogenetic evolution.
[Illustration: Fig. 118.--_Raia radiata_, representing the life size
of the youngest individual in which muscle fibres have been found
developing into electric cells].
[Illustration: Fig. 119.--Electric organ of the skate. The left-hand
drawing (i) represents the entire organ (natural size) of a
full-grown _r. radiata_. This is a small skate, which rarely exceeds
50 centms. in length; but in the large _r. batis_, the organ may
exceed two feet in length. The other drawings represent single
muscle-fibres in successive stages of transition. In the first of
the series (ii) the motor plate, and the nerves connected with it,
have already been considerably enlarged. In the other three
specimens, the fibre becomes more and more club-like, and eventually
cup-like. These changes of shape are expressive of great changes of
structure, as may be seen in the last of the series (v), where the
shallow cup is seen in partial section. The electric plate lines the
concavity of the cup, and is richly supplied with nerves (only a few
of which are represented in the last drawing); the thick walls of
the cup are composed of muscular fibres, the striation of which is
distinctly visible.]
[Illustration: Fig. 120.--Electric cells of _raia radiata_. The
drawing on the left represents one of the clubs magnified, as in the
preceding wood-cut. The drawing on the right represents a number of
these clubs, less highly magnified, _in situ_.]
Again, it cannot be answered that the principle of correlation may be
drawn upon in mitigation of the difficulty. The structure of the
electric organ is far too elaborate, far too specialized, and far too
obviously directed to a particular end, to admit of our conceivably
supposing it due to any accidental correlation with structural changes
going on elsewhere. Even as regards the initial changes of
muscle-elements into electrical-elements, I do not think the principle
of correlation can be reasonably adduced by way of explanation; for, as
shown in the illustrations, even this initial change is most
extraordinarily peculiar, elaborate, and specialized. But, be this as it
may, I am perfectly certain that the principle of correlation cannot
possibly be adduced to explain the subsequent _association of these
electrical elements into an electric battery_, actuated by a special
nervous mechanism of enormous size and elaboration--unless of course,
the progress of such a structure were assumed to have been throughout of
some utility. Under this supposition, however, the principle of
correlation would be forsaken in favour of that of natural selection;
and we should again be in the presence of the same difficulty as that
with which we started.
But now, and further, if we do thus abandon correlation in favour of
natural selection, and therefore if for the sake of saving an hypothesis
we assume that the organ as it now stands _must_ be of some use to the
existing skate, we should still have to face the question--Of what
conceivable use can those initial stages of its formation have been,
when first the muscle-elements began to be changed into the very
different electrical-elements, and when therefore they became useless as
muscles while not yet capable of performing even so much of the
electrical function as they now perform?
Lastly, we must remember that not only have we here the most highly
specialized, the most complex, and altogether the most elaboratively
adaptive organ in the animal kingdom; but also that in the formation of
this structure there has been needed an altogether unparalleled
expenditure of the most physiologically expensive of all
materials--namely, nervous tissue. Whether estimated by volume or by
weight, the quantity of nervous tissue which is consumed in the electric
organ of the skate is in excess of all the rest of the nervous system
put together. It is needless to say that nowhere else in the animal
kingdom--except, of course, in other electric fishes--is there any
approach to so enormous a development of nervous tissue for the
discharge of a special function. Therefore, as nervous tissue is,
physiologically speaking, the most valuable of all materials, we are
forced to conclude that natural selection ought strongly to have
_opposed_ the evolution of such organs, unless from the first moment of
their inception, and throughout the whole course of their development,
they were of some such paramount importance as biologically to justify
so unexampled an expenditure. Yet this paramount importance does not
admit of being so much as surmised, even where the organ has already
attained the size and degree of elaboration which it presents in the
skate.
In view of all these considerations taken together, I freely confess
that the difficulty presented by this case appears to me of a magnitude
and importance altogether unequalled by that of any other single
case--or any series of cases--which has hitherto been encountered by the
theory of natural selection. So that, if there were many other cases of
the like kind to be met with in nature, I should myself at once allow
that the theory of natural selection would have to be discarded. But
inasmuch as this particular case stands so far entirely by itself, and
therefore out of analogy with thousands, or even millions, of other
cases throughout the whole range of organic nature, I am constrained to
feel it more probable that the electric organ of the skate will some day
admit of being marshalled under the general law of natural selection--in
just the same way as proved to be the case with the conspicuous
colouring of those caterpillars, which, as explained in the last
chapter, at one time seemed to constitute a serious difficulty to the
theory, and yet, through a better knowledge of all the relations
involved, has now come to constitute one of the strongest witnesses in
its favour.
* * * * *
I have now stated all the objections of any importance which have
hitherto been brought against the theory of natural selection, excepting
three, which I left to be dealt with together because they form a
logically connected group. With a brief consideration of these,
therefore, I will bring this chapter to a close.
The three objections to which I allude are, (1) that a large
proportional number of specific, as well as of higher taxonomic
characters, are seemingly useless characters, and therefore do not lend
themselves to explanation by the Darwinian theory; (2) that the most
general of all specific characters--viz. cross-infertility between
allied species--cannot possibly be due to natural selection, as is
demonstrated by Darwin himself; (3) that the swamping effects of free
intercrossing must always render impossible by natural selection alone
any evolution of species in divergent (as distinguished from serial)
lines of change.
These three objections have been urged from time to time by not a few of
the most eminent botanists and zoologists of our century; and from one
point of view I cannot myself have the smallest doubt that the
objections thus advanced are not only valid in themselves, but also by
far the most formidable objections which the theory of natural selection
has encountered. From another point of view, however, I am equally
convinced that they all admit of absolute annihilation. This strong
antithesis arises, as I have said, from differences of standpoint, or
from differences in the view which we take of the theory of natural
selection itself. If we understand this theory to set forth natural
selection as the sole cause of organic evolution, then all the above
objections to the theory are not merely, as already stated, valid and
formidable, but as I will now add, logically insurmountable. On the
other hand, if we take theory to consist merely in setting forth natural
selection as a factor of organic evolution, even although we believe it
to have been the chief factor or principal cause, all the three
objections in question necessarily vanish. For in this case, even if it
be satisfactorily proved that the theory of natural selection is unable
to explain the three classes of facts above mentioned, the theory is not
thereby affected: facts of each and all of these classes may be
consistently left by the theory to be explained by causes other than
natural selection--whether these be so far capable or incapable of
hypothetical formulation. Thus it is evident that whether the three
objections above named are to be regarded as logically insurmountable by
the theory, or as logically non-existent in respect to it, depends
simply upon the manner in which the theory itself is stated.
In the next volume a great deal more will have to be said upon these
matters--especially with regard to the causes other than natural
selection which in my opinion are capable of explaining these so-called
"difficulties." In the present connexion, however, all I have attempted
to show is, that, whatever may be thought touching the supplementary
theories whereby I shall endeavour to explain the facts of inutility,
cross-sterility, and non-occurrence of free intercrossing, no one of
these facts is entitled to rank as an objection against the theory of
natural selection, unless we understand this theory to claim an
exclusive prerogative in the field of organic evolution. This, as we
have previously seen, is what Mr. Wallace does claim for it; while on
the other hand, Mr. Darwin expressly--and even vehemently--repudiates
the claim: from which it follows that all the three main objections
against the theory of natural selection are objections which vitally
affect the theory only as it has been stated and upheld by Wallace. As
the theory has been stated and upheld by Darwin, all these objections
are irrelevant. This is a fact which I had not myself perceived at the
time when I mentioned these objections in a paper entitled
_Physiological Selection_, which was published in 1886. The discussions
to which that paper gave rise, however, led me to consider these matters
more closely; and further study of Darwin's writings, with these matters
specially in view, has led me to see that none of the objections in
question are relevant to his theory, as distinguished from that of Mr.
Wallace. This, I acknowledge, I ought to have perceived before I
published the paper just alluded to; but in those days I had had no
occasion to follow out the differences between Darwin and Wallace to all
their consequences, and therefore adopted the prevalent view that their
theories of evolution were virtually identical. Now, however, I have
endeavoured to make it clear that the points wherein they differ involve
the important consequences above set forth. All these the most
formidable objections against the theory of natural selection arise
simply and solely from what I conceive to be the erroneous manner in
which the theory has been presented by Darwin's distinguished colleague.
* * * * *
I have now considered, as impartially as I can, all the main criticisms
and objections which have been brought against the theory of natural
selection; and the result is to show that, neither singly nor
collectively, are they entitled to much weight. On the other hand, as
we have seen in the preceding chapter, there is a vast accumulation of
evidence in favour of the theory. Hence, it is no wonder that the theory
has now been accepted by all naturalists, with scarcely any one notable
exception, as at any rate the best working hypothesis which has ever
been propounded whereby to explain the facts of organic evolution.
Moreover, in the opinion of those most competent to judge, the theory is
entitled to be regarded as something very much more than a working
hypothesis: it is held to be virtually a completed induction, or, in
other words, the proved exhibition of a general law, whereby the
causation of organic evolution admits of being in large part--if not
altogether--explained.
Now, whether or not we subscribe to this latter conclusion ought, I
think, to depend upon what we mean by an explanation in the case which
is before us. If we mean only that, given the large class of known facts
and unknown causes which are conveniently summarized under the terms
Heredity and Variability, then the further facts of Struggle and
Survival serve, in some considerable degree or another, to account for
the phenomena of adaptive evolution, I cannot see any room to question
that the evidence is sufficient to prove the statement. But it is clear
that by taking for granted these great facts of Heredity and
Variability, we have assumed the larger part of the problem as a whole.
Or, more correctly, by thus generalizing, in a merely verbal form, all
the unknown causes which are concerned in these two great factors of the
process in question, we are not so much as attempting to explain the
precedent causation which serves as a condition to the process. Much
more than half the battle would already have been won, had Darwin's
predecessors been able to explain the causes of Heredity and Variation;
hence it is but a very partial victory which we have hitherto gained in
our recent discovery of the effects of Struggle and Survival.
Yet partial though it be in relation to the whole battle, in itself, or
considered absolutely, there can be no reasonable doubt that it
constitutes the greatest single victory which has ever been gained by
the science of Biology. For this very reason, however, it behoves us to
consider all the more carefully the extent to which it goes. But my
discussion of this matter must be relegated to the next volume, where I
hope to give abundant proof of the soundness of Darwin's judgment as
conveyed in the words:--"I am convinced that natural selection has been
the main, but not the exclusive, means of modification."
CHAPTER X.
THE THEORY OF SEXUAL SELECTION, AND CONCLUDING REMARKS.
Although the explanatory value of the Darwinian theory of natural
selection is, as we have now seen, incalculably great, it nevertheless
does not meet those phenomena of organic nature which perhaps more than
any other attract the general attention, as well as the general
admiration, of mankind: I mean all that class of phenomena which go to
constitute the Beautiful. Whatever value beauty as such may have, it
clearly has not a life-preserving value. The gorgeous plumage of a
peacock, for instance, is of no advantage to the peacock in his struggle
for life, and therefore cannot be attributed to the agency of natural
selection. Now this fact of beauty in organic structures is a fact of
wide generality--almost as wide, indeed, as is the fact of their
utility. Mr. Darwin, therefore, suggested another hypothesis whereby to
render a scientific explanation of this fact. Just as by his theory of
natural selection he sought to explain the major fact of utility, so did
he endeavour to explain the minor fact of beauty by a theory of what he
termed Sexual Selection.
It is a matter of observation that the higher animals do not pair
indiscriminately; but that the members of either sex prefer those
individuals of the opposite sex which are to them most attractive. It is
important to understand _in limine_ that nobody has ever attempted to
challenge this statement. In other words, it is an unquestionable fact
that among many of the higher animals there literally and habitually
occurs a _sexual selection_; and this fact is not a matter of inference,
but, as I have said, a matter of observation. The inference only begins
where, from this observable fact, it is argued,--1st, that the sexual
selection has reference to an aesthetic taste on the part of the animals
themselves; and 2nd, that, supposing the selection to be determined by
such a taste, the cause thus given is adequate to explain the phenomena
of beauty which are presented by these animals. I will consider these
two points separately.
From the evidence which Darwin has collected, it appears to me
impossible to doubt that an aesthetic sense is displayed by many birds,
and not a few mammals. This of course does not necessarily imply that
the _standards_ of such a sense are the same as our own; nor does it
necessarily imply that there is any constant relation between such a
sense and high levels of intelligence in other respects. In point of
fact, such is certainly not the case, because the best evidence that we
have of an aesthetic sense in animals is derived from birds, and not from
mammals. The most cogent cases to quote in this connexion are those of
the numerous species of birds which habitually adorn their nests with
gaily coloured feathers, wool, cotton, or any other gaudy materials
which they may find lying about the woods and fields. In many cases a
marked preference is shown for particular objects--as, for instance, in
the case of the Syrian nut-hatch, which chooses the iridescent wings of
insects, or that of the great crested fly-catcher, which similarly
chooses the cast-off skins of snakes. But no doubt the most remarkable
of these cases is that of the baya-bird of Asia, which after having
completed its bottle-shaped and chambered nest[47], studs it over with
small lumps of clay, both inside and out, upon which the cock-bird
sticks fire-flies, apparently for the sole purpose of securing a
brilliantly decorative effect. Other birds, such as the hammer-head of
Africa, adorn the surroundings of their nests (which are built upon the
ground) with shells, bones, pieces of broken glass and earthenware, or
any objects of a bright and conspicuous character which they may happen
to find. The most consummate artists in this respect are, however, the
bower-birds; for the species of this family construct elaborate
play-houses in the form of arched tunnels, built of twigs upon the
ground. Through and around such a tunnel they chase one another; and it
is always observable that not only is the floor paved with a great
collection of shells, bones, coloured stones, and any other brilliant
objects which they are able to carry in their beaks, but also that the
walls are decorated with the most gaudy articles which the birds can
find. There is one genus, in Papua, which even goes so far as to provide
the theatre with a surrounding garden. A level piece of ground is
selected as a site for the building. The latter is about two feet high,
and constructed round the growing stalk of a shrub, which therefore
serves as a central pillar to which the frame-work of the roof is
attached. Twigs are woven into this frame-work until the whole is
rendered rain-proof. The tent thus erected is about nine feet in
circumference at its base, and presents a large arch as an entrance. The
central pillar is banked up with moss at its base, and a gallery is
built round the interior of the edifice. This gallery is decorated with
flowers, fruits, fungi, &c. These are also spread over the garden, which
covers about the same area as the play-house. The flowers are said to
be removed when they fade, while fresh ones are gathered to supply their
places. Thus the garden is always kept bright with flowers, as well as
with the brilliant green of mosses, which are collected and distributed
in patches, resembling tiny lawns.
[47] The chambers are three in number. The two upper ones are
occupied respectively by the male and the sitting female. The lower
one serves as a general living room when the young are hatched.
[Illustration: FIG. 121.--The Garden Bower-bird (_Amblyornis
inornata_). Reduced from _Gould's Birds of New Guinea_ to 1/4 nat.
size.]
Now these sundry cases alone seem to prove a high degree of the aesthetic
sense as occurring among birds; for, it is needless to say, none of the
facts just mentioned can be due to natural selection, seeing that they
have no reference to utility, or the preservation of life. But if an
aesthetic sense occurs in birds, we should expect, on _a priori_ grounds,
that it would probably be exercised with reference to the personal
appearance of the sexes. And this expectation is fully realized. For it
is an observable fact that in most species of birds where the males are
remarkable for the brilliancy of their plumage, not only is this
brilliancy most remarkable during the pairing season, but at this season
also the male birds take elaborate pains to display their charms before
the females. Then it is that the peacock erects his tail to strut round
and round the hens, taking care always to present to them a front view,
where the coloration is most gorgeous. And the same is true of all other
gaily coloured male birds. During the pairing season they actively
compete with one another in exhibiting their attractiveness to the
females; and in many cases there are added all sorts of extraordinary
antics in the way of dancings and crowings. Again, in the case of all
song-birds, the object of the singing is to please the females; and for
this purpose the males rival one another to the best of their musical
ability.
Thus there can be no question that the courtship of birds is a highly
elaborate business, in which the males do their best to surpass one
another in charming the females. Obviously the inference is that the
males do not take all this trouble for nothing; but that the females
give their consent to pair with the males whose personal appearance, or
whose voice, proves to be the most attractive. But, if so, the young of
the male bird who is thus _selected_ will inherit his superior beauty;
and thus, in successive generations, a continuous advance will be made
in the beauty of plumage or of song, as the case may be,--both the
origin and development of beauty in the animal world being thus supposed
due to the aesthetic taste of animals themselves.
Such is the theory of sexual selection in its main outlines; and with
regard to it we must begin by noting two things which are of most
importance. In the first place, it is a theory wholly and completely
distinct from the theory of natural selection; so that any truth or
error in the one does not in the least affect the other. The second
point is, that there is not so great a wealth of evidence in favour of
sexual selection as there is in favour of natural selection; and,
therefore, that while all naturalists nowadays accept natural selection
as _a_ (whether or not _the_) cause of adaptive, useful, or
life-preserving structures, there is no such universal--but only a very
general--agreement with reference to sexual selection as a cause of
decorative, beautiful, or life-embellishing structures. Nevertheless,
the evidence in favour of sexual selection is both large in amount and
massive in weight.
Our consideration of this evidence will bring us to the second division
of our subject, as previously marked out for discussion--namely,
granting that an aesthetic sense occurs in certain large divisions of the
animal kingdom, what is the proof that such a sense is a cause of the
beauty which is presented by the animals in question?
Before proceeding to state this proof, however, it is desirable to
observe that under the theory of sexual selection Darwin has included
two essentially different classes of facts. For besides the large class
of facts to which I have thus far been alluding,--i. e. the cases where
two sexes of the same species differ from one another in respect of
ornamentation,--there is another class of facts equally important,
namely, the cases where the two sexes of the same species differ from
one another in respect of size, strength, and the possession of natural
weapons, such as spurs, horns, &c. In most of these cases it is the
males which are thus superiorly endowed; and it is a matter of
observation that in all cases where they are so endowed they use their
superior strength and natural weapons for fighting together, in order to
secure possession of the females. Hence results what Mr. Darwin has
called the Law of Battle between males of the same species; and this law
of battle he includes under his theory of sexual selection. But it is
evident that the principle which is operative in the law of battle
differs from the principle which is concerned in the form of sexual
selection that has to do with embellishment, and consequent charm. The
law of battle, in fact, more nearly approaches the law of natural
selection; seeing that it expresses the natural advantages of brute
force in the struggling of rival animals, and so frequently results in
_death of the less fitted_, as distinguished from a mere failure to
propagate. Now against this doctrine of the law of battle, and the
consequences to which it leads in the superior fighting powers of male
animals, no objection has been raised in any quarter. It is only with
regard to the other aspect of the theory of sexual selection--or that
which is concerned with the superior embellishment of male animals--that
any difference of opinion obtains. I will now proceed to give the main
arguments on both sides of this question, beginning with a _resume_ of
the evidences in favour of sexual selection.
In the first place, the fact that secondary sexual characters of the
embellishing kind are so generally restricted to the male sex in itself
seems to constitute very cogent proof that, in some way or another, such
characters are connected with the part which is played by the male in
the act of propagation. Moreover, secondary sexual characters of this
kind are of quite as general occurrence as are those of the other kind
which have to do with rivalry in battle; and the former are usually of
the more elaborate description. Therefore, as there is no doubt that
secondary sexual characters of the one order have an immediate purpose
to serve in the act of propagation, we are by this close analogy
confirmed in our surmise that secondary sexual characters of the other,
and still more elaborate, order are likewise so concerned. Moreover,
this view of their meaning becomes still further strengthened when we
take into consideration the following facts. Namely, (_a_) secondary
sexual characters of the embellishing kind are, as a rule, developed
only at maturity; and most frequently during only a part of the year,
which is invariably the breeding season: (_b_) they are always more or
less seriously affected by emasculation: (_c_) they are always, and
only, displayed in perfection during the act of courtship: (_d_) then,
however, they are displayed with the most elaborate pains; yet always,
and only, before the females: (_e_) they appear, at all events in many
cases, to have the effect of charming the females into a performance of
the sexual act; while it is certain that in many cases, both among
quadrupeds and birds, individuals of the one sex are capable of feeling
a strong antipathy against, or a strong preference for, certain
individuals of the opposite sex.
Such are the main lines of evidence in favour of the theory of sexual
selection. And although it is enough that some of them should be merely
stated as above in order that their immense significance should become
apparent, in the case of others a bare statement is not sufficient for
this purpose. More especially is this the case as regards the enormous
profusion, variety, and elaboration of sexually-embellishing characters
which occur in birds and mammals--not to mention several divisions of
Arthropoda; together with the extraordinary amount of trouble which, in
a no less extraordinary number of different ways, is taken by the male
animals to display their embellishments before the females. And even in
many cases where to our eyes there is no particular embellishment to
display, the process of courtship consists in such an elaborate
performance of dancings, struttings, and attitudinizings that it is
scarcely possible to doubt their object is to incite the opposite sex.
Here, for instance, is a series of drawings illustrating the courtship
of spiders. I choose this case as an example, partly because it is the
one which has been published most recently, and partly because it is of
particular interest as occurring so low down in the zoological scale. I
am indebted to the kindness of Mr. and Mrs. Peckham for permission to
reproduce these few selected drawings from their very admirable work,
which is published by the Natural History Society of Wisconsin, U.S. It
is evident at a glance that all these elaborate, and to our eyes
ludicrous, performances are more suggestive of incitation than of any
other imaginable purpose. And this view of the matter is strongly
corroborated by the fact that it is the most brightly coloured parts of
the male spiders which are most obtruded upon the notice of the female
by these peculiar attitudes--in just the same way as is invariably the
case in the analogous phenomena of courtship among birds, insects, &c.
[Illustration: FIG. 122.--Courtship of Spiders. A few examples of
some of the attitudes adopted by different species of males when
approaching their females. (After Peckham.)]
[Illustration: FIG. 123.--Courtship of Spiders. Continued from Fig.
122, similarly showing some of the attitudes of approach adopted by
males of yet other different species. (After Peckham.)]
But so great is the mass of material which Darwin has collected in proof
of all the points mentioned in the foregoing paragraph, that to attempt
anything in the way of an epitome would really be to damage its
evidential force. Therefore I deem it best simply to refer to it as it
stands in his _Descent of Man_, concluding, as he concludes,--"This
surprising uniformity in the laws regulating the differences between the
sexes in so many and such widely separated classes is intelligible if we
admit the action throughout all the higher divisions of the animal
kingdom of one common cause, namely, sexual selection"; while, as he
might well have added, it is difficult to imagine that all the large
classes of facts which an admission of this common cause serves to
explain, can ever admit of being rendered intelligible by any other
theory.
We may next proceed to consider the objections which have been brought
against the theory of sexual selection. And this is virtually the same
thing as saying that we may now consider Mr. Wallace's views upon the
subject.
Reserving for subsequent consideration the most general of these
objections--namely, that at best the theory can only apply to the more
intelligent animals, and so must necessarily fail to explain the
phenomena of beauty in the less intelligent, or in the non-intelligent,
as well as in all species of plants--we may take _seriatim_ the other
objections which, in the opinion of Mr. Wallace, are sufficient to
dispose of the theory even as regards the higher animals.
In the first place, he argues that the principal cause of the greater
brilliancy of male animals in general, and of male birds in particular,
is that they do not so much stand in need of protection arising from
concealment as is the case with their respective females. Consequently
natural selection is not so active in repressing brilliancy of colour in
the males, or, which amounts to the same thing, is more active in
"repressing in the female those bright colours which are normally
produced in both sexes by general laws."
Next, he argues that not only does natural selection thus exercise a
negative influence in passively permitting more heightened colour to
appear in the males, but even exercises a positive influence in actively
promoting its development in the males, while, at the same time,
actively repressing its appearance in the females. For heightened
colour, he says, is correlated with health and vigour; and as there can
be no doubt that healthy and vigorous birds best provide for their
young, natural selection, by always placing its premium on health and
vigour in the males, thus also incidentally promotes, through correlated
growth, their superior coloration.
Again, with regard to the display which is practised by male birds, and
which constitutes the strongest of all Mr. Darwin's arguments in favour
of sexual selection, Mr. Wallace points out that there is no evidence of
the females being in any way affected thereby. On the other hand, he
argues that this display may be due merely to general excitement; and he
lays stress upon the more special fact that moveable feathers are
habitually erected under the influence of anger and rivalry, in order to
make the bird look more formidable in the eyes of antagonists.
Furthermore, he adduces the consideration that, even if the females are
in any way affected by colour and its display on the part of the males,
and if, therefore, sexual selection be conceded a true principle in
theory, still we must remember that, as a matter of fact, it can only
operate in so far as it is allowed to operate by natural selection. Now,
according to Mr. Wallace, natural selection must wholly neutralize any
such supposed influence of sexual selection. For, unless the survivors
in the general struggle for existence happen to be those which are also
the most highly ornamented, natural selection must neutralize and
destroy any influence that may be exerted by female selection. But
obviously the chances against the otherwise best fitted males happening
to be likewise the most highly ornamented must be many to one, unless,
as Wallace supposes, there is some correlation between embellishment and
general perfection, in which case, as he points out, the theory of
sexual selection lapses altogether, and becomes but a special case of
natural selection.
Once more, Mr. Wallace argues that the evidence collected by Mr. Darwin
himself proves that each bird finds a mate under any circumstances--a
general fact which in itself must quite neutralize any effect of sexual
selection of colour or ornament, since the less highly coloured birds
would be at no disadvantage as regards the leaving of healthy progeny.
Lastly, he urges the high improbability that through thousands of
generations all the females of any particular species--possibly spread
over an enormous area--should uniformly and always have displayed
exactly the same taste with respect to every detail of colour to be
presented by the males.
Now, without any question, we have here a most powerful array of
objections against the theory of sexual selection. Each of them is ably
developed by Mr. Wallace himself in his work on _Tropical Nature_; and
although I have here space only to state them in the most abbreviated of
possible forms, I think it will be apparent how formidable these
objections appear. Unfortunately the work in which they are mainly
presented was published several years after the second edition of the
_Descent of Man_, so that Mr. Darwin never had a suitable opportunity of
replying. But, if he had had such an opportunity, as far as I can judge
it seems that his reply would have been more or less as follows.
In the first place, Mr. Wallace fails to distinguish between brilliancy
and ornamentation--or between colour as merely "heightened," and as
distinctively decorative. Yet there is obviously the greatest possible
difference between these two things. We may readily enough admit that a
mere heightening of already existing coloration is likely enough--at all
events in many cases--to accompany a general increase of vigour, and
therefore that natural selection, by promoting the latter, may also
incidentally promote the former, in cases where brilliancy is not a
source of danger. But clearly this is a widely different thing from
showing that not only a _general brilliancy of colour_, but also _the
particular disposition of colours_, in the form of ornamental patterns,
can thus be accounted for by natural selection. Indeed, it is expressly
in order to account for the occurrence of such ornamental patterns that
Mr. Darwin constructed his theory of sexual selection; and therefore, by
thus virtually ignoring the only facts which that theory endeavours to
explain, Mr. Wallace is not really criticizing the theory at all. By
representing that the theory has to do only with brilliancy of colour,
as distinguished from disposition of colours, he is going off upon a
false issue which has never really been raised[48]. Look, for example,
at a peacock's tail. No doubt it is sufficiently brilliant; but far more
remarkable than its brilliancy is its elaborate pattern on the one hand,
and its enormous size on the other. There is no conceivable reason why
mere _brilliancy of colour_, as an accidental concomitant of general
vigour, should have run into so extraordinary, so elaborate, and so
beautiful a _design of colours_. Moreover, this design is only unfolded
when the tail is erected, and the tail is not erected in battle (as Mr.
Wallace's theory of the erectile function in feathers would require),
but in courtship; obviously, therefore, the purpose of the pattern, so
to speak, is correlated with the act of courtship--it being only then,
in fact, that the general purpose of the whole structure, as well as the
more special purpose of the pattern, becomes revealed. Lastly, the fact
of this whole structure being so large, entailing not only a great
amount of physiological material in its production, but also of
physiological energy in carrying about such a weight, as well as of
increased danger from impeding locomotion and inviting capture--all this
is obviously incompatible with the supposition of the peacock's tail
having been produced by natural selection. And such a case does not
stand alone. There are multitudes of other instances of ornamental
structures imposing a drain upon the vital energies of their possessors,
without conferring any compensating benefit from a utilitarian point of
view. Now, in all these cases, without any exception, such structures
are ornamental structures which present a plain and obvious reference to
the relationship of the sexes. Therefore it becomes almost impossible to
doubt--first, that they exist for the sake of ornament; and next, that
the ornament exists on account of that relationship. If such structures
were due merely to a superabundance of energy, as Mr. Wallace supposes,
not only ought they to have been kept down by the economizing influence
of natural selection; but we can see no reason, either why they should
be so highly ornamental on the one hand, or so exclusively related to
the sexual relationship on the other.
[48] Note C.
Finally, we must take notice of the fact that where peculiar
_structures_ are concerned for purposes of display in courtship, the
_elaboration_ of these structures is often no less remarkable than that
of patterns where colours are thus concerned. Take, for example, the
case of the Bell-bird, which I select from an innumerable number of
instances that might be mentioned because, while giving a verbal
description of this animal, Darwin does not supply a pictorial
representation thereof. The bird, which lives in South America, has a
very loud and peculiar call, that can be heard at a distance of two or
three miles. The female is dusky-green; but the adult male is a
beautiful white, excepting the extraordinary structure with which we are
at present concerned. This is a tube about three inches long, which
rises from the base of the beak. It is jet black, and dotted over with
small downy feathers. The tube is closed at the top, but its cavity
communicates with the palate, and thus the whole admits of being
inflated from within, when, of course, it stands erect as represented in
one of the two drawings. When not thus inflated, it hangs down, as
shown in the second figure, which represents the plumage of a young
male. (Fig. 124.)
[Illustration: FIG. 124.--The Bell-bird (_Chasmorhynchus niveus_,
1/4 natural size). Drawn from nature (_R. Coll. Surg. Mus._). In the
drawing of the adult male the ornamental appendage is represented in
its inflated condition, during courtship; in the drawing of the
young male it is shown in its flaccid condition.]
In another species of the genus there are three of these appendages--the
two additional ones being mounted on the corners of the mouth. (Fig.
125.) In all species of the genus (four in number) the tubes are
inflated during courtship, and therefore perform the function of sexual
embellishments. Now the point to which I wish to draw attention is, that
so specialized and morphologically elaborate a structure cannot be
regarded as merely adventitious. It must have been developed by some
definite cause, acting through a long series of generations. And as no
other function can be assigned to it than that of charming the female
when it is erected in courtship, the peculiarity of form and mechanism
which it presents--like the elaboration of patterns in cases where
colour only is concerned--virtually compels us to recognise in sexual
selection the only conceivable cause of its production.
[Illustration: FIG. 125.--_C. tricarunculatus_, 1/4 natural size.
Copied from the _Ibis_. The ornamental appendages of the male are
represented in a partly inflated condition.]
For these reasons I think that Mr. Wallace's main objection falls to the
ground. Passing on to his subsidiary objections, I do not see much
weight in his merely negative difficulty as to there being an absence of
evidence upon hen birds being charmed by the plumage, or the voice, of
their consorts. For, on the one hand, it is not very safe to infer what
sentiments may be in the mind of a hen; and, on the other hand, it is
impossible to conceive what motive can be in the mind of a cock, other
than that of making himself attractive, when he performs his various
antics, displays his ornamental plumes, or sings his melodious songs.
Considerations somewhat analogous apply to the difficulty of supposing
so much similarity and constancy of taste on the part of female animals
as Mr. Darwin's theory undoubtedly requires. Although we know very
little about the psychology of the lower animals, we do observe in many
cases that small details of mental organization are often wonderfully
constant and uniform throughout all members of a species, even where it
is impossible to suggest any utility as a cause.
Again, as regards the objection that each bird finds a mate under any
circumstances, we have here an obvious begging of the whole question.
That every feathered Jack should find a feathered Jill is perhaps what
we might have antecedently expected; but when we meet with innumerable
instances of ornamental plumes, melodious songs, and the rest, as so
many witnesses to a process of sexual selection having always been in
operation, it becomes irrational to exclude such evidence on account of
our antecedent prepossessions.
There remains the objection that the principles of natural selection
must necessarily swallow up those of sexual selection. And this
consideration, I doubt not, lies at the root of all Mr. Wallace's
opposition to the supplementary theory of sexual selection. He is
self-consistent in refusing to entertain the evidence of sexual
selection, on the ground of his antecedent persuasion that in the great
drama of evolution there is no possible standing-ground for any other
actor than that which appears in the person of natural selection. But
here, again, we must refuse to allow any merely antecedent presumption
to blind our eyes to the actual evidence of other agencies having
co-operated with natural selection in producing the observed results.
And, as regards the particular case now before us, I think I have shown,
as far as space will permit, that in the phenomena of decorative
colouring (as distinguished from merely brilliant colouring), of
melodious song (as distinguished from merely tuneless cries), of
enormous arborescent antlers (as distinguished from merely offensive
weapons), and so forth--I say that in all these phenomena we have
phenomena which cannot possibly be explained by the theory of natural
selection; and, further, that if they are to be explained at all, this
can only be done, so far as we can at present see, by Mr. Darwin's
supplementary theory of sexual selection.
I have now briefly answered all Mr. Wallace's objections to this
supplementary theory, and, as previously remarked, I feel pretty
confident that, at all events in the main, the answer is such as Mr.
Darwin would himself have supplied, had there been a third edition of
his work upon the subject. At all events, be this as it may, we are
happily in possession of unquestionable evidence that he believed all
Mr. Wallace's objections to admit of fully satisfactory answers. For his
very last words to science--read only a few hours before his death at a
meeting of the Zoological Society--were:
I may perhaps be here permitted to say that, after having carefully
weighed, to the best of my ability, the various arguments which
have been advanced against the principle of sexual selection, I
remain firmly convinced of its truth[49].
[49] Since the above exposition of the theory of sexual selection
was written, Mr. Poulton has published his work on the _Colours of
Animals_. He there reproduces some of the illustrations which occur
in Mr. and Mrs. Peckham's work on _Sexual Selection in Spiders_, and
furnishes appropriate descriptions. Therefore, while retaining the
illustrations, I have withdrawn my own descriptions.
Mr. Poulton has also in his book supplied a _resume_ of the
arguments for and against the theory of sexual selection in general.
Of course in nearly all respects this corresponds with the _resume_
which is given in the foregoing pages; but I have left the latter as
it was originally written, because all the critical part is
reproduced _verbatim_ from a review of Mr. Wallace's _Darwinism_, of
a date still earlier than that of Mr. Poulton's book--viz.
_Contemporary Review_, August, 1889.
_Concluding Remarks._
I will now conclude this chapter, and with it the present volume, by
offering a few general remarks on what may be termed the philosophical
relations of Darwinian doctrine to the facts of adaptation on the one
hand, and to those of beauty on the other. Of course we are all aware
that before the days of this doctrine the facts of adaptation in organic
nature were taken to constitute the clearest possible evidence of
special design, on account of the wonderful mechanisms which they
everywhere displayed; while the facts of beauty were taken as
constituting no less conclusive evidence of the quality of such special
design as beneficent, not to say artistic. But now that the Darwinian
doctrine appears to have explained scientifically the former class of
facts by its theory of natural selection, and the latter class of facts
by its theory of sexual selection, we may fitly conclude this brief
exposition of the doctrine as a whole by considering what influence such
naturalistic explanations may fairly be taken to exercise upon the
older, or super-naturalistic, interpretations.
To begin with the facts of adaptation, we must first of all observe that
the Darwinian doctrine is immediately concerned with these facts only in
so far as they occur in organic nature. With the adaptations--if they
can properly be so called--which occur in all the rest of nature, and
which go to constitute the Cosmos as a whole so wondrous a spectacle of
universal law and perfect order, this doctrine is but indirectly
concerned. Nevertheless, it is of course fundamentally concerned with
them to the extent that it seeks to bring the phenomena of organic
nature into line with those of inorganic; and therefore to show that
whatever view we may severally take as to the kind of causation which is
energizing in the latter we must now extend to the former. This is
usually expressed by saying that the theory of evolution by natural
selection is a mechanical theory. It endeavours to comprise all the
facts of adaptation in organic nature under the same category of
explanation as those which occur in inorganic nature--that is to say,
under the category of physical, or ascertainable, causation. Indeed,
unless the theory has succeeded in doing this, it has not succeeded in
doing anything--beyond making a great noise in the world. If Mr. Darwin
has not discovered a new mechanical cause in the selection principle,
his labour has been worse than in vain.
Now, without unduly repeating what has already been said in Chapter
VIII, I may remark that, whatever we may each think of the measure of
success which has thus far attended the theory of natural selection in
explaining the facts of adaptation, we ought all to agree that,
considered as a matter of general reasoning, the theory does certainly
refer to a _vera causa_ of a strictly physical kind; and, therefore,
that no exception can be taken to the theory in this respect on grounds
of _logic_. If the theory in this respect is to be attacked at all, it
can only be on grounds of _fact_--namely, by arguing that the cause does
not occur in nature, or that, if it does, its importance has been
exaggerated by the theory. Even, however, if the latter proposition
should ever be proved, we may now be virtually certain that the only
result would be the relegation of all the residual phenomena of
adaptation to other causes of the physical order--whether known or
unknown. Hence, as far as the matter of _principle_ is concerned, we may
definitely conclude that the great naturalistic movement of our century
has already brought all the phenomena of adaptation in organic nature
under precisely the same category of mechanical causation, as similar
movements in previous centuries have brought all the known phenomena of
inorganic nature: the only question that remains for solution is the
strictly _scientific_ question touching the particular causes of the
mechanical order which have been at work.
So much, then, for the phenomena of adaptation. Turning next to those of
beauty, we have already seen that the theory of sexual selection stands
to these in precisely the same relation as the theory of natural
selection does to those of adaptation. In other words, it supplies a
physical explanation of them; because, as far as our present purposes
are concerned, it may be taken for granted, or for the sake of argument,
that inasmuch as psychological elements enter into the question the
cerebral basis which they demand involves a physical side.
There is, moreover, this further point of resemblance between the two
theories: neither of them has any reference to inorganic nature.
Therefore, with the charm or the loveliness of landscapes, of earth and
sea and sky, of pebbles, crystals, and so forth, we have at present
nothing to do. How it is that so many inanimate objects are invested
with beauty--why it is that beauty attaches to architecture, music,
poetry, and many other things--these are questions which do not
specially concern the biologist. If they are ever to receive any
satisfactory explanation in terms of natural causation, this must be
furnished at the hands of the psychologist. It may be possible for him
to show, more satisfactorily than hitherto, that all beauty, whenever
and wherever it occurs, is literally "in the eyes of the beholder"; or
that objectively considered, there is no such thing as beauty. It may
be--and in my opinion it probably is--purely an affair of the percipient
mind itself, depending on the association of ideas with pleasure-giving
objects. This association may well lead to a liking for such objects,
and so to the formation of what is known as aesthetic feeling with regard
to them. Moreover, beauty of inanimate nature must be an affair of the
percipient mind itself, unless there be a creating intelligence with
organs of sense and ideals of beauty similar to our own. And, apart from
any deeper considerations, this latter possibility is scarcely entitled
to be regarded as a probability, looking to the immense diversities in
those ideals among different races of mankind. But, be this as it may,
the scientific problem which is presented by the fact of aesthetic
feeling, even if it is ever to be satisfactorily solved, is a problem
which, as already remarked, must be dealt with by psychologists. As
biologists we have simply to accept this feeling as a fact, and to
consider how, out of such a feeling as a cause, the beauty of organic
nature may have followed as an effect.
Now we have already seen how the theory of sexual selection supposes
this to have happened. But against this theory a formidable objection
arises, and one which I have thought it best to reserve for treatment in
this place, because it serves to show the principal difference between
Mr. Darwin's two great generalizations, considered as generalizations in
the way of mechanical theory. For while the theory of natural selection
extends equally throughout the whole range of organic nature, the theory
of sexual selection has but a comparatively restricted scope, which,
moreover, is but vaguely defined. For it is obvious that the theory can
only apply to living organisms which are sufficiently intelligent to
admit of our reasonably accrediting them with aesthetic taste--namely, in
effect, the higher animals. And just as this consideration greatly
restricts the possible scope of the theory, as compared with that of
natural selection, so does it render undefined the zoological limits
within which it can be reasonably employed. Lastly, this necessarily
undefined, and yet most important limitation exposes the theory to the
objection just alluded to, and which I shall now mention.
The theory, as we have just seen, is necessarily restricted in its
application to the higher animals. Yet the facts which it is designed to
explain are not thus restricted. For beauty is by no means restricted to
the higher animals. The whole of the vegetable world, and the whole of
the animal world at least as high up in the scale as the insects, must
be taken as incapable of aesthetic feeling. Therefore, the extreme
beauty of flowers, sea-anemones, corals, and so forth, cannot possibly
be ascribed to sexual selection.
Now, with regard to this difficulty, we must begin by excluding the case
of the vegetable kingdom as irrelevant. For it has been rendered highly
probable--if not actually proved--by Darwin and others, that the beauty
of flowers and of fruits is in large part due to natural selection. It
is to the advantage of flowering plants that their organs of
fructification should be rendered conspicuous--and in many cases also
odoriferous,--in order to attract the insects on which the process of
fertilization depends. Similarly, it is to the advantage of all plants
which have brightly coloured fruits that these should be conspicuous for
the purpose of attracting birds, which eat the fruits and so disseminate
the seed. Hence all the gay colours and varied forms, both of flowers
and fruits, have been thus adequately explained as due to natural
causes, working for the welfare, as distinguished from the beauty, of
the plants. For even the distribution of colours on flowers, or the
beautiful patterns which so many of them present, are found to be useful
in guiding insects to the organs of fructification.
Again, the green colouring of leaves, which lends so much beauty to the
vegetable world, has likewise been shown to be of vital importance to
the physiology of plant-life; and, therefore, may also be ascribed to
natural selection. Thus, there remains only the forms of plants other
than the flowers. But the forms of leaves have also in many cases been
shown to be governed by principles of utility; and the same is to be
said of the branching structure which is so characteristic of trees and
shrubs, since this is the form most effectual for spreading out the
leaves to the light and air. Here, then, we likewise find that the cause
determining plant beauty is natural selection; and so we may conclude
that the only reason why the forms of trees which are thus determined by
utility appeal to us as beautiful, is because we are accustomed to these
the most ordinary forms. Our ideas having been always, as it were,
moulded upon these forms, aesthetic feeling becomes attached to them by
the principle of association. At any rate, it is certain that when we
contemplate almost any forms of plant-structure which, for special
reasons of utility, differ widely from these (to us) more habitual
forms, the result is not suggestive of beauty. Many of the tropical and
un-tree-like plants--such as the cactus tribe--strike us as odd and
quaint, not as beautiful. Be this however as it may, I trust I have said
enough to prove that in the vegetable world, at all events, the
attainment of beauty cannot be held to have been an object aimed at, so
to speak, for its own sake. Even if, for the purposes of argument, we
were to suppose that all the forms and colours in the vegetable world
are due to special design, there could be no doubt that the purpose of
this design has been in chief part a utilitarian purpose; it has not
aimed at beauty exclusively for its own sake. For most of such beauty as
we here perceive is plainly due to the means adopted for the attainment
of life-preserving ends, which, of course, is a metaphorical way of
saying that it is probably due to natural selection[50].
[50] The beauty of autumnal tints in fading leaves may possibly be
adduced _per contra_. But here we have to remember that it is only
some kinds of leaves which thus become beautiful when fading, while,
even as regards those that do, it is not remarkable that their
chlorophyll should, as it were, accidentally assume brilliant tints
while breaking down into lower grades of chemical constitution. The
case, in fact, is exactly parallel to those in the animal kingdom
which are considered in the ensuing paragraphs.
Turning, then, to the animal kingdom below the level of insects, here we
are bound to confess that the beauty which so often meets us cannot
reasonably be ascribed either to natural or to sexual selection. Not to
sexual selection for the reasons already given; the animals in question
are neither sufficiently intelligent to possess any aesthetic taste, nor,
as a matter of fact, do we observe that they exercise any choice in
pairing. Not to natural selection, because we cannot here, as in the
case of vegetables, point to any benefit as generally arising from
bright colours and beautiful forms. On the principles of naturalism,
therefore, we are driven to conclude that the beauty here is purely
adventitious, or accidental. Nor need we be afraid to make this
admission, if only we take a sufficiently wide view of the facts. For,
when we do take such a view, we find that beauty here is by no means of
invariable, or even of general, occurrence. There is no loveliness about
an oyster or a lob-worm; parasites, as a rule, are positively ugly, and
they constitute a good half of all animal species. The truth seems to
be, when we look attentively at the matter, that in all cases where
beauty does occur in these lower forms of animal life, its presence is
owing to one of two things--either to the radiate form, or to the bright
tints. Now, seeing that the radiate form is of such general occurrence
among these lower animals--appearing over and over again, with the
utmost insistence, even among groups widely separated from one another
by the latest results of scientific classification--seeing this, it
becomes impossible to doubt that the radiate form is due to some
morphological reasons of wide generality. Whether these reasons be
connected with the internal laws of growth, or to the external
conditions of environment, I do not pretend to suggest. But I feel safe
in saying that it cannot possibly be due to any design to secure beauty
for its own sake. The very generality of the radiate form is in itself
enough to suggest that it must have some physical, as distinguished from
an aesthetic, explanation; for, if the attainment of beauty had here been
the object, surely it might have been even more effectually accomplished
by adopting a greater variety of typical forms--as, for instance, in the
case of flowers.
Coming then, lastly, to the case of brilliant tints in the lower
animals, Mr. Darwin has soundly argued that there is nothing forced or
improbable in the supposition that organic compounds, presenting as they
do such highly complex and such varied chemical constitutions, should
often present brilliant colouring _incidentally_. Considered merely as
colouring, there is nothing in the world more magnificent than arterial
blood; yet here the colouring is of purely utilitarian significance. It
is of the first importance in the chemistry of respiration; but is
surely without any meaning from an aesthetic point of view. For the
colour of the cheeks, and of the flesh generally, in the _white_ races
of mankind, could have been produced quite as effectually by the use of
pigment--as in the case of certain monkeys. Now the fact that in the
case of blood, as in that of many other highly coloured fluids and
solids throughout the animal kingdom, the colour is _concealed_, is
surely sufficient proof that the colour, if regarded from an aesthetic
point of view, is accidental. Therefore, when, as in other cases, such
colouring occurs upon the surface, and thus becomes apparent, are we not
irresistibly led to conclude that its _exhibition_ in such cases is
likewise accidental, so far as any question of aesthetic design is
concerned?
I have now briefly glanced at all the main facts of organic nature with
reference to beauty; and, as a result, I think it is impossible to
resist the general conclusion, that in organic nature beauty does not
exist as an end _per se_. All cases where beauty can be pointed to in
organic nature are seemingly due--either to natural selection, acting
without reference to beauty, but to utility; to sexual selection, acting
with reference to the taste of animals; or else to sheer accident. And
if this general conclusion should be held to need any special
verification, is it not to be found in the numberless cases where
organic nature not only fails to be beautiful, but reveals itself as the
reverse. Not again to refer to the case of parasites, what can be more
unshapely than a hippopotamus, or more generally repulsive than a
crocodile? If it be said that these are exceptions, and that the forms
of animals as a rule are graceful, the answer--even apart from
parasites--is obvious. In all cases where the habits of life are such as
to render rapid locomotion a matter of utilitarian necessity, the
outlines of an animal _must_ be graceful--else, whether the locomotion
be terrestrial, aerial, or aquatic, it must fail to be swift. Hence it
is only in such cases as that of the hippopotamus, rhinoceros,
elephant, crocodile, and so forth, where natural selection has had no
concern in developing speed, that the accompanying accident of
gracefulness can be allowed to disappear. But if beauty in organic
nature had been in itself what may be termed an artistic object on the
part of a divine Creator, it is absurd to suggest that his design in
this matter should only have been allowed to appear where we are able to
detect other and very good reasons for its appearance.
* * * * *
Thus, whether we look to the facts of adaptation or to those of beauty,
everywhere throughout organic nature we meet with abundant evidence of
natural causation, while nowhere do we meet with any independent
evidence of supernatural design. But, having led up to this conclusion,
and having thus stated it as honestly as I can, I should like to finish
by further stating what, in my opinion is its logical bearing upon the
more fundamental tenets of religious thought.
As I have already observed at the commencement of this brief exposition,
prior to the Darwinian theory of organic evolution, the theologian was
prone to point to the realm of organic nature as furnishing a peculiarly
rich and virtually endless store of facts, all combining in their
testimony to the wisdom and the beneficence of the Deity. Innumerable
adaptations of structures to functions appeared to yield convincing
evidence in favour of design; the beauty so profusely shed by living
forms appeared to yield evidence, no less convincing, of that design as
beneficent. But both these sources of evidence have now, as it were,
been tapped at their fountain-head: the adaptation and the beauty are
alike receiving their explanation at the hands of a purely mechanical
philosophy. Nay, even the personality of man himself is assailed; and
this not only in the features which he shares with the lower animals,
but also in his god-like attributes of reason, thought, and conscience.
All nature has thus been transformed before the view of the present
generation in a manner and to an extent that has never before been
possible: and inasmuch as the change which has taken place has taken
place in the direction of naturalism, and this to the extent of
rendering the mechanical interpretation of nature universal, it is no
wonder if the religious mind has suddenly awakened to a new and a
terrible force in the words of its traditional enemy--Where is now thy
God?
This is not the place to discuss the bearings of science on
religion[51]; but I think it is a place where one may properly point out
the limits within which no such bearings obtain. Now, from what has just
been said, it will be apparent that I am not going to minimise the
change which has been wrought. On the contrary, I believe it is only
stupidity or affectation which can deny that the change in question is
more deep and broad than any single previous change in the whole history
of human thought. It is a fundamental, a cosmical, a world-transforming
change. Nevertheless, in my opinion, it is a change of a non-theistic,
as distinguished from an a-theistic, kind. It has rendered impossible
the appearance in literature of any future Paley, Bell, or Chalmers; but
it has done nothing in the way of negativing that belief in a Supreme
Being which it was the object of these authors to substantiate. If it
has demonstrated the futility of their proof, it has furnished nothing
in the way of disproof. It has shown, indeed, that their line of
argument was misjudged when they thus sought to separate organic nature
from inorganic as a theatre for the special or peculiar display of
supernatural design; but further than this it has not shown anything.
The change in question therefore, although greater in degree, is the
same in kind as all its predecessors: like all previous advances in
cosmological theory which have been wrought by the advance of science,
this latest and greatest advance has been that of revealing the
constitution of nature, or the method of causation, as everywhere the
same. But it is evident that this change, vast and to all appearance
final though it be, must end within the limits of natural causation
itself. The whole world of life and mind may now have been annexed to
that of matter and energy as together constituting one magnificent
dominion, which is everywhere subject to the same rule, or method of
government. But the ulterior and ultimate question touching the nature
of this government as mental or non-mental, personal or impersonal,
remains exactly where it was. Indeed, this is a question which cannot be
affected by _any_ advance of science, further than science has proved
herself able to dispose of erroneous arguments based upon ignorance of
nature. For while the sphere of science is necessarily restricted to
that of natural causation which it is her office to explore, the
question touching the _nature of this natural causation_ is one which as
necessarily lies without the whole sphere of such causation itself:
therefore it lies beyond any possible intrusion by science. And not only
so. But if the nature of natural causation be that of the highest order
of known existence, then, although we must evidently be incapable of
conceiving what such a Mind is, at least we seem capable of judging what
in many respects it is not. It cannot be more than one; it cannot be
limited either in space or time; it cannot be other than at least as
self-consistent as its manifestations in nature are invariable. Now,
from the latter deduction there arises a point of first-rate importance
in the present connexion. For if the so-called First Cause be
intelligent, and therefore all secondary causes but the expression of a
supreme Will, in as far as such a Will is self-consistent, the operation
of all natural causes must be uniform,--with the result that, as seen by
us, this operation must needs appear to be what we call mechanical. The
more unvarying the Will, the more unvarying must be this expression
thereof; so that, if the former be absolutely self-consistent, the
latter cannot fail to be as reasonably interpreted by the theory of
mindless necessity, as by that of ubiquitous intention. Such being, as
it appears to me, the pure logic of the matter, the proof of organic
evolution amounts to nothing more than the proof of a natural process.
What mode of being is ultimately concerned in this process--or in what
it is that this process ultimately consists--is a question upon which
science is as voiceless as speculation is vociferous.
[51] The best treatise on this subject is Prof. Le Conte's
_Evolution and its Relation to Religious Thought_ (Appleton & Co.
1888).
But, it may still be urged, surely the principle of natural selection
(with its terrible basis in the struggle for existence) and the
principle of sexual selection (with its consequence in denying beauty
to be an end in itself) demonstrate that, _if_ there be design in
nature, such design at all events cannot be beneficent. To this,
however, I should again reply that, just as touching the major question
of design itself, so as touching this minor question of the quality of
such design as beneficent, I do not see how the matter has been much
affected by a discovery of the principles before us. For we did not need
a Darwin to tell us that the whole creation groaneth and travaileth
together in pain. The most that in this connexion Darwin can fairly be
said to have done is to have estimated in a more careful and precise
manner than any of his predecessors, the range and the severity of this
travail. And if it be true that the result of what may be called his
scientific analysis of nature in respect of suffering is to have shown
the law of suffering even more severe, more ubiquitous, and more
necessary than it had ever been shown before, we must remember at the
same time how he has proved, more rigidly than was ever proved before,
that suffering is a condition to improvement--struggle for life being
the _raison d'etre_ of higher life, and this not only in the physical
sphere, but also in the mental and moral.
Lastly, if it be said that the _choice_ of such a method, whereby
improvement is only secured at the cost of suffering, indicates a kind
of callousness on the part of an intelligent Being supposed to be
omnipotent, I confess that such does appear to me a legitimate
conclusion--subject, however, to the reservation that higher knowledge
might displace it. For, as far as matters are now actually presented to
the unbiased contemplation of a human mind, this provisional inference
appears to me unavoidable--namely, that if the world of sentient life be
due to an Omnipotent Designer, the aim or motive of the design must have
been that of securing a continuous advance of animal improvement,
without any regard at all to animal suffering. For I own it does not
seem to me compatible with a fair and honest exercise of our reason to
set the sum of animal happiness over against the sum of animal misery,
and then to allege that, in so far as the former tends to balance--or to
over-balance--the latter, thus far is the moral character of the design
as a whole vindicated. Even if it could be shown that the sum of
happiness in the brute creation considerably preponderates over that of
unhappiness--which is the customary argument of theistic apologists,--we
should still remain without evidence as to this state of matters having
formed any essential part of the design. On the other hand, we should
still be in possession of seemingly good evidence to the contrary. For
it is clearly a condition to progress by survival of the fittest, that
as soon as organisms become sentient selection must be exercised with
reference to sentiency; and this means that, if further progress is to
take place, states of sentiency _must_ become so organized with
reference to habitual experience of the race, that pleasures and pains
shall answer respectively to states of agreement and disagreement with
the sentient creature's environment. Those animals which found pleasure
in what was deleterious to life would not survive, while those which
found pleasure in what was beneficial to life would survive; and so
eventually, in every species of animal, states of sentiency as agreeable
or disagreeable must approximately correspond with what is good for the
species or bad for the species. Indeed, we may legitimately surmise that
the reason why sentiency (and, _a fortiori_, conscious volition) has
ever appeared upon the scene at all, has been because it
furnishes--through this continuously selected adjustment of states of
sentiency to states of the sentient organism--so admirable a means of
securing rapid, and often refined, adjustments by the organism to the
habitual conditions of its life[52]. But, if so, not only is this state
of matters a _condition_ to progress in the future; it is further, and
equally, a _consequence_ of progress in the past.
[52] See _Mental Evolution in Animals_, pp. 110-111.
However, be this as it may, from all that has gone before does it not
become apparent that pleasure or happiness on the one hand, and pain or
misery on the other, must be present in sentient nature? And so long as
they are both seen to be equally necessary under the process of
evolution by natural selection, we have clearly no more reason to regard
the pleasure than the pain as an object of the supposed design. Rather
must we see in both one and the same condition to progress under the
method of natural causation which is before us; and therefore I cannot
perceive that it makes much difference--so far as the argument for
beneficence is concerned--whether the pleasures of animals outweigh
their pains, or _vice versa_.
Upon the whole, then, it seems to me that such evidence as we have is
against rather than in favour of the inference, that if design be
operative in animate nature it has reference to animal enjoyment or
well-being, as distinguished from animal improvement or evolution. And
if this result should be found distasteful to the religious mind--if it
be felt that there is no desire to save the evidences of design unless
they serve at the same time to testify to the nature of that design as
beneficent,--I must once more observe that the difficulty thus presented
to theism is not a difficulty of modern creation. On the contrary, it
has always constituted the fundamental difficulty with which natural
theologians have had to contend. The external world appears, in this
respect, to be at variance with our moral sense; and when the antagonism
is brought home to the religious mind, it must ever be with a shock of
terrified surprise. It has been newly brought home to us by the
generalizations of Darwin; and therefore, as I said at the beginning,
the religious thought of our generation has been more than ever
staggered by the question--Where is now thy God? But I have endeavoured
to show that the logical standing of the case has not been materially
changed; and when this cry of Reason pierces the heart of Faith, it
remains for Faith to answer now, as she has always answered before--and
answered with that trust which is at once her beauty and her
life--Verily thou art a God that hidest thyself.
_APPENDIX AND NOTES_
APPENDIX TO CHAPTER V.
ON OBJECTIONS WHICH HAVE BEEN BROUGHT AGAINST THE THEORY OF ORGANIC
EVOLUTION ON GROUNDS OF PALAEONTOLOGY.
While stating in the text, and in a necessarily general way, the
evidence which is yielded by palaeontology to the theory of organic
evolution, I have been desirous of not overstating it. Therefore, in the
earlier paragraphs of the chapter, which deal with the most general
heads of such evidence, I introduced certain qualifying phrases; and I
will now give the reasons which led me to do so.
Of all the five biological sciences which have been called into
evidence--viz. those of Classification, Morphology, Embryology,
Palaeontology, and Geographical Distribution--it is in the case of
palaeontology alone that any important or professional opinions still
continue to be unsatisfied. Therefore, in order that justice may be done
to this line of dissent, I have thought it better to deal with the
matter in a separate Appendix, rather than to hurry it over in the text.
And, as all the difficulties or objections which have been advanced
against the theory of evolution on grounds of palaeontology must vary, as
to their strength, with the estimate which is taken touching the degree
of imperfection of the geological record, I will begin by adding a few
paragraphs to what has already been said in the text upon this subject.
First, then, as to the difficulties in the way of fossils being formed
at all. We have already noticed in the text that it is only the more or
less hard parts of organisms which under any circumstances can be
fossilized; and even the hardest parts quickly disintegrate if not
protected from the weather on land, or from the water on the sea-bottom.
Moreover, as Darwin says, "we probably take a quite erroneous view when
we assume that sediment is being deposited over nearly the whole bed of
the sea, at a rate sufficiently quick to embed and preserve fossil
remains. Throughout an enormously large proportion of the ocean, the
bright blue tint of the water bespeaks its purity. The many cases on
record of a formation conformably covered, after an immense interval of
time, by another and a later formation, without the underlying bed
having suffered in the interval any wear and tear, seem explicable only
on the view of the bottom of the sea not rarely lying for ages in an
unaltered condition." Next, as regards littoral animals, he shows the
difficulty which they must have in becoming fossils, and gives a
striking example in several of the existing species of a sub-family of
cirripedes (_Chthamalinae_), "which coat the rocks all over the world in
infinite numbers," yet, with the exception of one species which inhabits
deep water, no vestige of any of them has been found in any tertiary
formation, although it is known that the genus _Chthamalus_ existed
through the Chalk period. Lastly, "with respect to the terrestrial
productions which lived through the secondary and palaeozoic periods, it
is superfluous to state our evidence is fragmentary in an extreme
degree. For instance, until recently not a land shell was known
belonging to either of these vast periods," with one exception; while,
"in regard to mammiferous remains, a glance at the historical table in
Lyell's Manual will bring home the truth, how accidental and rare has
been their preservation, far better than pages of detail. Nor is their
rarity surprising, when we remember how large a proportion of the bones
of tertiary mammals have been discovered either in caves or in
lacustrine deposits; and that not a cave or true lacustrine bed is known
belonging to the age of our secondary or palaeozoic formations."
But perhaps of even more importance than all these known causes which
prevent the formation of fossils, is the existence of unknown causes
which make for the same result. For example, the Flysch-formation is a
formation of several thousand feet in thickness (as much as 6000 in some
places), and it extends for at least 300 miles from Vienna to
Switzerland; moreover, it consists of shale and sandstone. Therefore,
alike in respect of time, space, and character, it is just such a
formation as we should expect to find highly rich in fossils; yet,
"although this great mass has been most carefully searched, no fossils,
except a few vegetable remains, have been found."
So much then for the difficulty, so to speak, which nature experiences
in the manufacture of fossils. Probably not one per cent. of the species
of animals which have inhabited the earth has left a single individual
as a fossil, whereby to record its past existence.
But of even more importance than this difficulty of making fossils in
the first instance, is the difficulty of preserving them when they are
made. The vast majority of fossils have been formed under water, and a
large proportional number of these--whether the animals were marine,
terrestrial, or inhabitants of fresh water--have been formed in
sedimentary deposits either of sand, gravel, or other porous material.
Now, where such deposits have been afterwards raised into the air for
any considerable time--and this has been more or less the case with all
deposits which are available for exploration--their fossiliferous
contents will have been, as a general rule, dissolved by the percolation
of rain-water charged with carbonic acid. Similarly, sea-water has
recently been found to be a surprisingly strong solvent of calcareous
material: hence, Saturn-like, the ocean devours her own progeny as far
as shells and bones of all kinds are concerned--and this to an extent of
which we have probably no adequate conception.
Of still greater destructive influence, however, than these solvent
agencies in earth and sea, are the erosive agencies of both. Any one who
watches the pounding of the waves upon the shore; who then observes the
effect of it upon the rocks broken into shingle, and on the shingle
reduced to sand; who, looking behind him at the cliffs, sees there the
evidence of the gradual advance of this all-pulverising power--an
advance so gradual that no yard of it is accomplished until within that
yard the "white teeth" have eaten well into the "bowels of the earth";
who then reflects that this process is going on simultaneously over
hundreds of thousands of miles of coast-lines throughout the world; and
who finally extends his mental vision from space to time, by trying
dimly to imagine what this ever-roaring monster must have consumed
during the hundreds of millions of years that slowly rising and slowly
sinking continents have exposed their whole areas to her jaws; whoever
thus observes and thus reflects must be a dull man, if he does not begin
to feel that in the presence of such a destroyer as this we have no
reason to wonder at a frequent silence in the testimony of the rocks.
But although the erosive agency of the sea is thus so inconceivably
great, it is positively small if compared with erosive agencies on land.
The constant action of rain, wind, and running water, in wearing down
the surfaces of all lands into "the dust of continents to be"; the
disintegrating effects on all but the very hardest rocks of winter
frosts alternating with summer heats; the grinding power of ice in
periods of glaciation; and last, but not least, the wholesale melting up
of sedimentary formations whenever these have sunk for any considerable
distance beneath the earth's surface:--all these agencies taken together
constitute so prodigious a sum of energies combined through
immeasureable ages in their common work of destruction, that when we
try to realise what it must amount to, we can scarcely fail to wonder,
not that the geological record is highly imperfect, but that so much of
the record has survived as we find to have been the case. And, if we add
to these erosive and solvent agencies on land the erosive and solvent
agencies of the sea, we may almost begin to wonder that anything
deserving the name of a geological record is in existence at all.
That such estimates of the destructive powers of nature are not mere
matters of speculative reasoning may be amply shown by stating one
single fact, which, like so many others where the present subject is
concerned, we owe to the generalizations of Darwin. Plutonic rocks,
being those which have emerged from subterranean heat of melting
intensity, must clearly at some time or another have lain beneath the
whole thickness of sedimentary deposits, which at that time occupied any
part of the earth's surface where we now find the Plutonic rocks exposed
to view. Or, in other words, wherever we now find Plutonic rocks at the
surface of the earth, we must conclude that all the sedimentary rocks by
which they were covered when in a molten state have since been entirely
destroyed; several vertical miles of the only kinds of rocks in which
fossils can possibly occur must in all such cases have been abolished
_in toto_. Now, in many parts of the world metamorphic rocks--which have
thus gradually risen from Plutonic depths, while miles of various other
rock-formations have been removed from their now exposed surfaces--cover
immense areas, and therefore testify by their present horizontal range,
no less than by their previously vertical depth, to the enormous scale
on which a total destruction has taken place of everything that once lay
above them. For instance, the granitic region of Parime is at least
nineteen times the size of Switzerland; a similar region south of the
Amazon is probably larger than France, Spain, Italy, and Great Britain
all put together; and, more remarkable still, over the area of the
United States and Canada, granitic rocks exceed in the proportion of 19
to 12-1/2 the whole of the newer Palaeozoic formations. Lastly, after
giving these examples, Darwin adds the important consideration, that "in
many regions the metamorphic and granitic rocks would be found much more
widely extended than they appear to be, if all the sedimentary beds were
removed which rest unconformably on them, and which could not have
formed part of the original mantle under which they were crystallized."
The above is a brief condensation of the already condensed statement
which Darwin has given of the imperfection of the geological record; but
I think it is enough to show, in a general way, how precarious must be
the nature of any objections to the theory of evolution which are
founded merely upon the silence of palaeontology in cases where, if the
record were anything like complete, we should be entitled to expect from
it some positive information. But, as we have seen in the text,
imperfect though the record be, in as far as it furnishes positive
information at all, this is well-nigh uniformly in favour of the theory;
and therefore, even on grounds of palaeontology alone, it appears to me
that Darwin is much too liberal where he concludes his discussion by
saying,--"Those who believe that the geological record is in any degree
perfect, will undoubtedly at once reject the theory." If in any measure
reasonable, such persons ought rather to examine their title to such a
belief; and even if they disregard the consensus of testimony which is
yielded by all the biological sciences to the theory of evolution, they
ought at least to hold their judgment in suspense until they shall have
not only set against the apparently negative testimony which is yielded
by geology its unquestionably positive testimony, but also well
considered the causes which may--or rather must--have so gravely
impaired the geological record.
However, be this as it may, I will now pass on to consider the
difficulties and objections which have been brought against the theory
on grounds of palaeontology.
These may be classified under four heads. First, the absence of varietal
links between allied species; second, the sudden appearance of whole
groups of species--not only as genera and families, but even sometimes
as orders and classes--without any forms leading up to them; third, the
occurrence of highly organized types at much lower levels of geological
strata than an evolutionist would antecedently expect; and, fourth, the
absence of fossils of any kind lower down than the Cambrian strata.
Now all these objections depend on estimates of the imperfection of the
geological record much lower than that which is formed by Darwin.
Therefore I have arranged the objections in their order of difficulty in
this respect, or in the order that requires successively increasing
estimates of the imperfection of the record, if they are to be
successively answered.
I think that the first of them has been already answered in the text, by
showing that even a very moderate estimate of the imperfection of the
record is enough to explain why intermediate _varieties_, connecting
allied _species_, are but comparatively seldom met with. Moreover it was
shown that in some cases, where shells are concerned, remarkably
well-connected series of such varieties have been met with. And the same
applies to species and genera in certain other cases, as in the equine
family.