branched, or star-like spiculae in many sponges, which are believed to
have the function chiefly, of rendering them unpalatable to other
creatures. The Holothuridae or sea-cucumbers possess a similar
protection, many of them having anchor-shaped spicules embedded in their
skin, as the Synapta; while others (Cuviera squamata) are covered with a
hard calcareous pavement. Many of these are of a bright red or purple
colour, and are very conspicuous, while the allied Trepang, or
Beche-de-mer (Holothuria edulis), which is not armed with any such
defensive weapons, is of a dull sand-or mud-colour, so as hardly to be
distinguished from the sea bed on which it reposes. Many of the smaller
marine animals are protected by their almost invisible transparency,
while those that are most brightly coloured will be often found to have
a special protection, either in stinging tentacles like Physalia, or in
a hard calcareous crust, as in the star fishes.
_Females of some Groups require and obtain more Protection than the
Males._
In the struggle for existence incessantly going on, protection or
concealment is one of the most general and most effectual means of
maintaining life; and it is by modifications of colour that this
protection can be most readily obtained, since no other character is
subject to such numerous and rapid variations. The case I have now
endeavoured to illustrate is exactly analogous to what occurs among
butterflies. As a general rule, the female butterfly is of dull and
inconspicuous colours, even when the male is most gorgeously arrayed;
but when the species is protected from attack by a disagreeable odour,
as in the Heliconidae, Danaidae and Acroeidae, both sexes display the same
or equally brilliant hues. Among the species which gain a protection by
imitating these, the very weak and slow-flying Leptalides resemble them
in both sexes, because both sexes alike require protection, while in the
more active and strong-winged genera--Papilio, Pieris, and Diadema--it
is generally the females only that mimic the protected groups, and in
doing so often become actually more gay and more conspicuous than the
males, thus reversing the usual and in fact almost universal characters
of the sexes. So, in the wonderful Eastern leaf-insects of the genus
Phyllium, it is the female only that so marvellously imitates a green
leaf; and in all these cases the difference can be traced to the greater
need of protection for the female, on whose continued existence, while
depositing her eggs, the safety of the race depends. In Mammalia and in
reptiles, however brilliant the colours may be, there is rarely any
difference between that of the sexes, because the female is not
necessarily more exposed to attack than the male. It may, I think, be
looked upon as a confirmation of this view, that no single case is known
either in the above-named genera--Papilio, Pieris, and Diadema--or in
any other butterfly, of a male _alone_, mimicking one of the Danaidae or
Heliconidae. Yet the necessary colour is far more abundant in the males,
and variations always seem ready for any useful purpose. This seems to
depend on the general law, that each species and each sex can only be
modified just as far as is absolutely necessary for it to maintain
itself in the struggle for existence, not a step further. A male insect
by its structure and habits is less exposed to danger, and also requires
less protection than the female. It cannot, therefore, alone acquire any
further protection through the agency of natural selection. But the
female requires some extra protection, to balance the greater danger to
which she is exposed, and her greater importance to the existence of the
species; and this she always acquires, in one way or another, through
the action of natural selection.
In his "Origin of Species," fourth edition, p. 241, Mr. Darwin
recognises the necessity for protection as sometimes being a cause of
the obscure colours of female birds; but he does not seem to consider it
so very important an agent in modifying colour as I am disposed to do.
In the same paragraph (p. 240), he alludes to the fact of female birds
and butterflies being sometimes very plain, sometimes as gay as the
males; but, apparently, considers this mainly due to peculiar laws of
inheritance, which sometimes continue acquired colour in the line of one
sex only, sometimes in both. Without denying the action of such a law
(which Mr. Darwin informs me he has facts to support), I impute the
difference, in the great majority of cases, to the greater or less need
of protection in the female sex in these groups of animals.
This need was seen to exist a century ago by the Hon. Daines Barrington,
who, in the article already quoted (see p. 220), after alluding to the
fact that singing birds are all small, and suggesting (but I think
erroneously) that this may have arisen from the difficulty larger birds
would have in concealing themselves if they called the attention of
their enemies by loud notes, goes on thus:--"I should rather conceive it
is for the same reason no hen bird sings, because this talent would be
still more dangerous during incubation, which _may possibly also account
for the inferiority in point of plumage_." This is a curious
anticipation of the main idea on which this essay is founded. It has
been unnoticed for near a century, and my attention was only recently
called to it by Mr. Darwin himself.
_Conclusion._
To some persons it will perhaps appear, that the causes to which I
impute so much of the external aspect of nature are too simple, too
insignificant, and too unimportant for such a mighty work. But I would
ask them to consider, that the great object of all the peculiarities of
animal structure is to preserve the life of the individual, and to
maintain the existence of the species. Colour has hitherto been too
often looked upon as something adventitious and superficial, something
given to an animal not to be useful to itself, but solely to gratify man
or even superior beings--to add to the beauty and ideal harmony of
nature. If this were the case, then, it is evident that the colours of
organised beings would be an exception to most other natural phenomena.
They would not be the product of general laws, or determined by
ever-changing external conditions; and we must give up all enquiry into
their origin and causes, since (by the hypothesis) they are dependent on
a Will whose motives must ever be unknown to us. But, strange to say, no
sooner do we begin to examine and classify the colours of natural
objects, than we find that they are intimately related to a variety of
other phenomena, and are, like them, strictly subordinated to general
laws. I have here attempted to elucidate some of these laws in the case
of birds, and have shown how the mode of nidification has affected the
colouring of the female sex in this group. I have before shown to how
great an extent, and in how many ways, the need of protection has
determined the colours of insects, and of some groups of reptiles and
mammalia, and I would now call particular attention to the fact that the
gay tints of flowers, so long supposed to be a convincing proof that
colour has been bestowed for other purposes than the good of its
possessor, have been shown by Mr. Darwin to follow the same great law of
utility. Flowers do not often need protection, but very often require
the aid of insects to fertilize them, and maintain their reproductive
powers in the greatest vigour. Their gay colours attract insects, as do
also their sweet odours and honeyed secretions; and that this is the
main function of colour in flowers is shown by the striking fact, that
those flowers which can be perfectly fertilized by the wind, and do not
need the aid of insects, _rarely or never have gaily-coloured flowers_.
This wide extension of the general principle of utility to the colours
of such varied groups, both in the animal and vegetable kingdoms,
compels us to acknowledge that the "reign of law" has been fairly traced
into this stronghold of the advocates of special creation. And to those
who oppose the explanation I have given of the facts adduced in this
essay, I would again respectfully urge that they must grapple with the
whole of the facts, not one or two of them only. It will be admitted
that, on the theory of evolution and natural selection, a wide range of
facts with regard to colour in nature have been co-ordinated and
explained. Until at least an equally wide range of facts can be shown to
be in harmony with any other theory, we can hardly be expected to
abandon that which has already done such good service, and which has led
to the discovery of so many interesting and unexpected harmonies among
the most common (but hitherto most neglected and least understood), of
the phenomena presented by organised beings.
VIII.
CREATION BY LAW.
Among the various criticisms that have appeared on Mr. Darwin's
celebrated "Origin of Species," there is, perhaps, none that will appeal
to so large a number of well educated and intelligent persons, as that
contained in the Duke of Argyll's "Reign of Law." The noble author
represents the feelings and expresses the ideas of that large class, who
take a keen interest in the progress of Science in general, and
especially that of Natural History, but have never themselves studied
nature in detail, or acquired that personal knowledge of the structure
of closely allied forms,--the wonderful gradations from species to
species and from group to group, and the infinite variety of the
phenomena of "variation" in organic beings,--which are absolutely
necessary for a full appreciation of the facts and reasonings contained
in Mr. Darwin's great work.
Nearly half of the Duke's book is devoted to an exposition of his idea
of "Creation by Law," and he expresses so clearly what are his
difficulties and objections as regards the theory of "Natural
Selection," that I think it advisable that they should be fairly
answered, and that his own views should be shown to lead to conclusions,
as hard to accept as any which he imputes to Mr. Darwin.
The point on which the Duke of Argyll lays most stress, is, that proofs
of Mind everywhere meet us in Nature, and are more especially manifest
wherever we find "contrivance" or "beauty." He maintains that this
indicates the constant supervision and direct interference of the
Creator, and cannot possibly be explained by the unassisted action of
any combination of laws. Now, Mr. Darwin's work has for its main object,
to show, that all the phenomena of living things,--all their wonderful
organs and complicated structures, their infinite variety of form, size,
and colour, their intricate and involved relations to each other,--may
have been produced by the action of a few general laws of the simplest
kind, laws which are in most cases mere statements of admitted facts.
The chief of these laws or facts are the following:--
1. _The Law of Multiplication in Geometrical Progression._--All
organized beings have enormous powers of multiplication. Even man, who
increases slower than all other animals, could under the most favourable
circumstances double his numbers every fifteen years, or a hundred-fold
in a century. Many animals and plants could increase their numbers from
ten to a thousand-fold every year.
2. _The Law of Limited Populations._--The number of living individuals
of each species in any country, or in the whole globe, is practically
stationary; whence it follows that the whole of this enormous increase
must die off almost as fast as produced, except only those individuals
for whom room is made by the death of parents. As a simple but striking
example, take an oak forest. Every oak will drop annually thousands or
millions of acorns, but till an old tree falls, not one of these
millions can grow up into an oak. They must die at various stages of
growth.
3. _The Law of Heredity, or Likeness of Offspring to their
Parents._--This is a universal, but not an absolute law. All creatures
resemble their parents in a high degree, and in the majority of cases
very accurately; so that even individual peculiarities, of whatever
kind, in the parents, are almost always transmitted to some of the
offspring.
4. _The Law of Variation._--This is fully expressed by the lines:--
"No being on this earthly ball,
Is like another, all in all."
Offspring resemble their parents very much, but not wholly--each being
possesses its individuality. This "variation" itself varies in amount,
but it is always present, not only in the whole being, but in every part
of every being. Every organ, every character, every feeling is
individual; that is to say, _varies_ from the same organ, character, or
feeling in every other individual.
5. _The Law of unceasing Change of Physical Conditions upon the Surface
of the Earth._--Geology shows us that this change has always gone on in
times past, and we also know that it is now everywhere going on.
6. _The Equilibrium or Harmony of Nature._--When a species is well
adapted to the conditions which environ it, it flourishes; when
imperfectly adapted it decays; when ill-adapted it becomes extinct. If
_all_ the conditions which determine an organism's well-being are taken
into consideration, this statement can hardly be disputed.
* * * * *
This series of facts or laws, are mere statements of what is the
condition of nature. They are facts or inferences which are generally
known, generally admitted--but in discussing the subject of the "Origin
of Species"--as generally forgotten. It is from these universally
admitted facts, that the origin of all the varied forms of nature may be
deduced by a logical chain of reasoning, which, however, is at every
step verified and shown to be in strict accord with facts; and, at the
same time, many curious phenomena which can by no other means be
understood, are explained and accounted for. It is probable, that these
primary facts or laws are but results of the very nature of life, and of
the essential properties of organized and unorganized matter. Mr.
Herbert Spencer, in his "First Principles" and his "Biology" has, I
think, made us able to understand how this may be; but at present we may
accept these simple laws without going further back, and the question
then is--whether the variety, the harmony, the contrivance, and the
beauty we perceive in organic beings, can have been produced by the
action of these laws alone, or whether we are required to believe in the
incessant interference and direct action of the mind and will of the
Creator. It is simply a question of how the Creator has worked. The
Duke (and I quote him as having well expressed the views of the more
intelligent of Mr. Darwin's opponents) maintains, that He has personally
applied general laws to produce effects, which those laws are not in
themselves capable of producing; that the universe alone, with all its
laws intact, would be a sort of chaos, without variety, without harmony,
without design, without beauty; that there is not (and therefore we may
presume that there could not be) any self-developing power in the
universe. I believe, on the contrary, that the universe is so
constituted as to be self-regulating; that as long as it contains Life,
the forms under which that life is manifested have an inherent power of
adjustment to each other and to surrounding nature; and that this
adjustment necessarily leads to the greatest amount of variety and
beauty and enjoyment, because it does depend on general laws, and not on
a continual supervision and re-arrangement of details. As a matter of
feeling and religion, I hold this to be a far higher conception of the
Creator and of the Universe than that which may be called the "continual
interference" hypothesis; but it is not a question to be decided by our
feelings or convictions, it is a question of facts and of reason. Could
the change, which Geology shows us has ever taken place in the forms of
life, have been produced by general laws, or does it imperatively
require the incessant supervision of a creative mind? This is the
question for us to consider, and our opponents have the difficult task
of proving a negative, if we show that there are both facts and
analogies in our favour.
_Mr. Darwin's Metaphors liable to Misconception._
Mr. Darwin has laid himself open to much misconception, and has given to
his opponents a powerful weapon against himself, by his continual use of
metaphor in describing the wonderful co-adaptations of organic beings.
"It is curious," says the Duke of Argyll, "to observe the language
which this most advanced disciple of pure naturalism instinctively
uses, when he has to describe the complicated structure of this curious
order of plants (the Orchids). 'Caution in ascribing intentions to
nature,' does not seem to occur to him as possible. Intention is the one
thing which he does see, and which, when he does not see, he seeks for
diligently until he finds it. He exhausts every form of words and of
illustration, by which intention or mental purpose can be described.
'Contrivance'--'curious contrivance,'--'beautiful contrivance,'--these
are expressions which occur over and over again. Here is one sentence
describing the parts of a particular species: 'the Labellum is developed
into a long nectary, _in order_ to attract Lepidoptera, and we shall
presently give reason for suspecting that the nectar is _purposely_ so
lodged, that it can be sucked only slowly _in order_ to give time for
the curious chemical quality of the viscid matter setting hard and
dry.'" Many other examples of similar expressions are quoted by the
Duke, who maintains that no explanation of these "contrivances" has
been or can be given, except on the supposition of a personal contriver,
specially arranging the details of each case, although causing them to
be produced by the ordinary processes of growth and reproduction.
Now there is a difficulty in this view of the origin of the structure of
Orchids which the Duke does not allude to. The majority of flowering
plants are fertilized, either without the agency of insects or, when
insects are required, without any very important modification of the
structure of the flower. It is evident, therefore, that flowers might
have been formed as varied, fantastic, and beautiful as the Orchids, and
yet have been fertilized without more complexity of structure than is
found in Violets, or Clover, or Primroses, or a thousand other flowers.
The strange springs and traps and pitfalls found in the flowers of
Orchids cannot be necessary _per se_, since exactly the same end is
gained in ten thousand other flowers which do not possess them. Is it
not then an extraordinary idea, to imagine the Creator of the Universe
_contriving_ the various complicated parts of these flowers, as a
mechanic might contrive an ingenious toy or a difficult puzzle? Is it
not a more worthy conception that they are some of the results of those
general laws which were so co-ordinated at the first introduction of
life upon the earth as to result necessarily in the utmost possible
development of varied forms?
But let us take one of the simpler cases adduced and see if our general
laws are unable to account for it.
_A Case of Orchis-structure explained by Natural Selection._
There is a Madagascar Orchis--the Angraecum sesquipedale--with an
immensely long and deep nectary. How did such an extraordinary organ
come to be developed? Mr. Darwin's explanation is this. The pollen of
this flower can only be removed by the base of the proboscis of some
very large moths, when trying to get at the nectar at the bottom of the
vessel. The moths with the longest probosces would do this most
effectually; they would be rewarded for their long tongues by getting
the most nectar; whilst on the other hand, the flowers with the deepest
nectaries would be the best fertilized by the largest moths preferring
them. Consequently, the deepest nectaried Orchids and the longest
tongued moths would each confer on the other an advantage in the battle
of life. This would tend to their respective perpetuation, and to the
constant lengthening of nectaries and probosces. Now let it be
remembered, that what we have to account for, is only the unusual length
of this organ. A nectary is found in many orders of plants and is
especially common in the Orchids, but in this one case only is it more
than a foot long. How did this arise? We begin with the fact, proved
experimentally by Mr. Darwin, that moths do visit Orchids, do thrust
their spiral trunks into the nectaries, and do fertilize them by
carrying the pollinia of one flower to the stigma of another. He has
further explained the exact mechanism by which this is effected, and
the Duke of Argyll admits the accuracy of his observations. In our
British species, such as Orchis pyramidalis, it is not necessary that
there should be any exact adjustment between the length of the nectary
and that of the proboscis of the insect; and thus a number of insects of
various sizes are found to carry away the pollinia and aid in the
fertilization. In the Angraecum sesquipedale, however, it is necessary
that the proboscis should be forced into a particular part of the
flower, and this would only be done by a large moth burying its
proboscis to the very base, and straining to drain the nectar from the
bottom of the long tube, in which it occupies a depth of one or two
inches only. Now let us start from the time when the nectary was only
half its present length or about six inches, and was chiefly fertilized
by a species of moth which appeared at the time of the plant's
flowering, and whose proboscis was of the same length. Among the
millions of flowers of the Angraecum produced every year, some would
always be shorter than the average, some longer. The former, owing to
the structure of the flower, would not get fertilized, because the moths
could get all the nectar without forcing their trunks down to the very
base. The latter would be well fertilized, and the longest would on the
average be the best fertilized of all. By this process alone the average
length of the nectary would annually increase, because, the
short-nectaried flowers being sterile and the long ones having abundant
offspring, exactly the same effect would be produced as if a gardener
destroyed the short ones and sowed the seed of the long ones only; and
this we know by experience would produce a regular increase of length,
since it is this very process which has increased the size and changed
the form of our cultivated fruits and flowers.
But this would lead in time to such an increased length of the nectary
that many of the moths could only just reach the surface of the nectar,
and only the few with exceptionally long trunks be able to suck up a
considerable portion.