filled out its wings, and till the warmth and sunlight have given it
strength. For the wings are by origin a part of the breathing
apparatus, and they require to be plimmed by the air before the insect
can take to flight. Then, as it grows more accustomed to its new life,
the hereditary impulse causes it to spread its vans abroad, and it
flies. Soon a flower catches its eye, and the bright mass of colour
attracts it irresistibly, as the candle-light attracts the eye of a
child a few weeks old. It sets off towards the patch of red or yellow,
probably not knowing beforehand that this is the visible symbol of food
for it, but merely guided by the blind habit of its race, imprinted
with binding force in the very constitution of its body. Thus the
moths, which fly by night and visit only white flowers whose corollas
still shine out in the twilight, are so irresistibly led on by the
external stimulus of light from a candle falling upon their eyes that
they cannot choose but move their wings rapidly in that direction; and
though singed and blinded twice or three times by the flame, must still
wheel and eddy into it, till at last they perish in the scorching
blaze. Their instincts, or, to put it more clearly, their simple
nervous mechanism, though admirably adapted to their natural
circumstances, cannot be equally adapted to such artificial objects as
wax candles. The butterfly in like manner is attracted automatically by
the colour of his proper flowers, and settling upon them, sucks up
their honey instinctively. But feeding is not now his only object in
life: he has to find and pair with a suitable mate. That, indeed, is
the great end of his winged existence. Here, again, his simple nervous
system stands him in good stead. The picture of his kind is, as it
were, imprinted on his little brain, and he knows his own mates the
moment he sees them, just as intuitively as he knows the flowers upon
which he must feed. Now we see the reason for the butterfly's large
optic centres: they have to guide it in all its movements. In like
manner, and by a like mechanism, the female butterfly or moth selects
the right spot for laying her eggs, which of course depends entirely
upon the nature of the young caterpillars' proper food. Each great
group of insects has its own habits in this respect, may-flies laying
their eggs on the water, many beetles on wood, flies on decaying animal
matter, and butterflies mostly on special plants. Thus throughout its
whole life the butterfly's activity is entirely governed by a rigid
law, registered and fixed for ever in the constitution of its ganglia
and motor nerves. Certain definite objects outside it invariably
produce certain definite movements on the insect's part. No doubt it is
vaguely conscious of all that it does: no doubt it derives a faint
pleasure from due exercise of all its vital functions, and a faint pain
when they are injured or thwarted; but on the whole its range of action
is narrowed and bounded by its hereditary instincts and their nervous
correlatives. It may light on one flower rather than another; it may
choose a fresher and brighter mate rather than a battered and dingy
one; but its little subjectivity is a mere shadow compared with ours,
and it hardly deserves to be considered as more than a semi-conscious
automatic machine.
XVI.
_BUTTERFLY ÆSTHETICS._
The other day, when I was watching that little red-spotted butterfly
whose psychology I found so interesting, I hardly took enough account,
perhaps, of the insect's own subjective feelings of pleasure and pain.
The first great point to understand about these minute creatures is
that they are, after all, mainly pieces of automatic mechanism: the
second great point is to understand that they are probably something
more than that as well. To-day I have found another exactly similar
butterfly, and I am going to work out with myself the other half of the
problem about him. Granted that the insect is, viewed intellectually, a
cunning bit of nervous machinery, may it not be true at the same time
that he is, viewed emotionally, a faint copy of ourselves?
Here he stands on a purple thistle again, true, as usual, to the plant
on which I last found him. There can be no doubt that he distinguishes
one colour from another, for you can artificially attract him by
putting a piece of purple paper on a green leaf, just as the flower
naturally attracts him with its native hue. Numerous observations and
experiments have proved with all but absolute certainty that his
discrimination of colour is essentially identical with our own; and I
think, if we run our eye up and down nature, observing how universally
all animals are attracted by pure and bright colours, we can hardly
doubt that he appreciates and admires colour as well as discriminates
it. Mr. Darwin certainly judges that butterflies can show an æsthetic
preference of the sort, for he sets down their own lovely hues to the
constant sexual selection of the handsomest mates. We must not,
however, take too human a measure of their capacities in this respect.
It is sufficient to believe that the insect derives some direct
enjoyment from the stimulation of pure colour, and is hereditarily
attracted by it wherever it may show itself. This pleasure draws it on,
on the one hand, towards the gay flowers which form its natural food;
and, on the other hand, towards its own brilliant mates. Imprinted on
its nervous system is a certain blank form answering to its own
specific type; and when the object corresponding to this blank form
occurs in its neighbourhood, the insect blindly obeys its hereditary
instinct. But out of two or three such possible mates it naturally
selects that which is most brightly spotted, and in other ways most
perfectly fulfils the specific ideal. We need not suppose that the
insect is conscious of making a selection or of the reasons which guide
it in its choice: it is enough to believe that it follows the strongest
stimulus, just as the child picks out the biggest and reddest apple
from a row of ten. Yet such unconscious selections, made from time to
time in generation after generation, have sufficed to produce at last
all the beautiful spots and metallic eyelets of our loveliest English
or tropical butterflies. Insects always accustomed to exercising their
colour-sense upon flowers and mates, may easily acquire a high standard
of taste in that direction, while still remaining comparatively in a
low stage as regards their intellectual condition. But the fact I wish
especially to emphasise is this--that the flowers produced by the
colour-sense of butterflies and their allies are just those objects
which we ourselves consider most lovely in nature; and that the marks
and shades upon their own wings, produced by the long selective action
of their mates, are just the things which we ourselves consider most
beautiful in the animal world. In this respect, then, there seems to be
a close community of taste and feeling between the butterfly and
ourselves.
Let me note, too, just in passing, that while the upper half of the
butterfly's wing is generally beautiful in colour, so as to attract his
fastidious mate, the under half, displayed while he is at rest, is
almost always dull, and often resembles the plant upon which he
habitually alights. The first set of colours is obviously due to sexual
selection, and has for its object the making of an effective courtship;
but the second set is obviously due to natural selection, and has been
produced by the fact that all those insects whose bright colours show
through too vividly when they are at rest fall a prey to birds or other
enemies, leaving only the best protected to continue the life of the
species.
But sight is not the only important sense to the butterfly. He is
largely moved and guided by smell as well. Both bees and butterflies
seem largely to select the flowers they visit by means of smell, though
colour also aids them greatly. When we remember that in ants scent
alone does duty instead of eyes, ears, or any other sense, it would
hardly be possible to doubt that other allied insects possessed the
same faculty in a high degree; and, as Dr. Bastian says, there seems
good reason for believing that all the higher insects are guided almost
as much by smell as by sight. Now it is noteworthy that most of those
flowers which lay themselves out to attract bees and butterflies are
not only coloured but sweetly scented; and it is to this cause that we
owe the perfumes of the rose, the lily-of-the-valley, the heliotrope,
the jasmine, the violet, and the stephanotis. Night-flowering plants,
which depend entirely for their fertilisation upon moths, are almost
always white, and have usually very powerful perfumes. Is it not a
striking fact that these various scents are exactly those which human
beings most admire, and which they artificially extract for essences?
Here, again, we see that the æsthetic tastes of butterflies and men
decidedly agree; and that the thyme or lavender whose perfume pleases
the bee is the very thing which we ourselves choose to sweeten our
rooms.
Finally, if we look at the sense of taste, we find an equally curious
agreement between men and insects; for the honey which is stored by the
flower for the bee, and by the bee for its own use, is stolen and eaten
up by man instead. Hence, when I consider the general continuity of
nervous structure throughout the whole animal race, and the exact
similarity of the stimulus in each instance, I can hardly doubt that
the butterfly really enjoys life somewhat as we enjoy it, though far
less vividly. I cannot but think that he finds honey sweet, and
perfumes pleasant, and colour attractive; that he feels a lightsome
gladness as he flits in the sunshine from flower to flower, and that he
knows a faint thrill of pleasure at the sight of his chosen mate. Still
more is this belief forced upon me when I recollect that, so far as I
can judge, throughout the whole animal world, save only in a few
aberrant types, sugar is sweet to taste, and thyme to smell, and song
to hear, and sunshine to bask in. Therefore, on the whole, while I
admit that the butterfly is mainly an animated puppet, I must qualify
my opinion by adding that it is a puppet which, after its vague little
fashion, thinks and feels very much as we do.
XVII.
_THE ORIGIN OF WALNUTS._
Mr. Darwin has devoted no small portion of his valuable life to
tracing, in two bulky volumes, the Descent of Man. Yet I suppose it is
probable that in our narrow anthropinism we should have refused to
listen to him had he given us two volumes instead on the Descent of
Walnuts. Viewed as a question merely of biological science, the one
subject is just as important as the other. But the old Greek doctrine
that 'man is the measure of all things' is strong in us still. We form
for ourselves a sort of pre-Copernican universe, in which the world
occupies the central point of space, and man occupies the central point
of the world. What touches man interests us deeply: what concerns him
but slightly we pass over as of no consequence. Nevertheless, even the
origin and development of walnuts is a subject upon which we may
profitably reflect, not wholly without gratification and interest.
This kiln-dried walnut on my plate, which has suggested such abstract
cogitations to my mind, is shown by its very name to be a foreign
production; for the word contains the same root as Wales and Welsh, the
old Teutonic name for men of a different race, which the Germans still
apply to the Italians, and we ourselves to the last relics of the old
Keltic population in Southern Britain. It means 'the foreign nut,' and
it comes for the most part from the south of Europe. As a nut, it
represents a very different type of fruit from the strawberry and
raspberry, with their bright colours, sweet juices, and nutritious
pulp. Those fruits which alone bear the name in common parlance are
attractive in their object; the nuts are deterrent. An orange or a plum
is brightly tinted with hues which contrast strongly with the
surrounding foliage; its pleasant taste and soft pulp all advertise it
for the notice of birds or monkeys, as a means for assisting in the
dispersion of its seed. But a nut, on the contrary, is a fruit whose
actual seed contains an abundance of oils and other pleasant
food-stuffs, which must be carefully guarded against the depredations
of possible foes. In the plum or the orange we do not eat the seed
itself: we only eat the surrounding pulp. But in the walnut the part
which we utilise is the embryo plant itself; and so the walnut's great
object in life is to avoid being eaten. Accordingly, that part of the
fruit which in the plum is stored with sweet juices is, in the walnut,
filled with a bitter and very nauseous essence. We seldom see this
bitter covering in our over-civilised life, because it is, of course,
removed before the nuts come to table. The walnut has but a thin shell,
and is poorly protected in comparison with some of its relations, such
as the American butternut, which can only be cracked by a sharp blow
from a hammer--or even the hickory, whose hard covering has done more
to destroy the teeth of New Englanders than all other causes put
together, and New England teeth are universally admitted to be the very
worst in the world. Now, all nuts have to guard against squirrels and
birds; and therefore their peculiarities are exactly opposite to those
of succulent fruits. Instead of attracting attention by being brightly
coloured, they are invariably green like the leaves while they remain
on the tree, and brown or dusky like the soil when they fall upon the
ground beneath; instead of being enclosed in sweet coats, they are
provided with bitter, acrid, or stinging husks; and, instead of being
soft in texture, they are surrounded by hard shells, like the coco-nut,
or have a perfectly solid kernel, like the vegetable ivory.
The origin of nuts is thus exactly the reverse side of the origin of
fruits. Certain seeds, richly stored with oils and starches for aiding
the growth of the young plant, are exposed to the attacks of squirrels,
monkeys, parrots, and other arboreal animals. The greater part of them
are eaten and completely destroyed by these their enemies, and so never
hand down their peculiarities to any descendants. But all fruits vary a
little in sweetness and bitterness, pulpy or stringy tendencies. Thus a
few among them happen to be protected from destruction by their
originally accidental possession of a bitter husk, a hard shell, or a
few awkward spines and bristles. These the monkeys and squirrels
reject; and they alone survive as the parents of future generations.
The more persistent and the hungrier their foes become, the less will a
small degree of bitterness or hardness serve to protect them. Hence,
from generation to generation, the bitterness and the hardness will go
on increasing, because only those nuts which are the nastiest and the
most difficult to crack will escape destruction from the teeth or bills
of the growing and pressing population of rodents and birds. The nut
which best survives on the average is that which is least conspicuous
in colour, has a rind of the most objectionable taste, and is enclosed
in the most solid shell. But the extent to which such precautions
become necessary will depend much upon the particular animals to whose
attacks the nuts of each country are exposed. The European walnut has
only to defy a few small woodland animals, who are sufficiently
deterred by its acrid husk; the American butter-nut has to withstand
the long teeth of much more formidable forestine rodents, whom it sets
at nought with its stony and wrinkled shell; and the tropical cocos and
Brazil nuts have to escape the monkey, who pounds them with stones, or
flings them with all his might from the tree-top so as to smash them in
their fall against the ground below.
Our own hazel-nut supplies an excellent illustration of the general
tactics adopted by the nuts at large. The little red tufted blossoms
which everybody knows so well in early spring are each surrounded by a
bunch of three bracts; and as the nut grows bigger, these bracts form a
green leaf-like covering, which causes it to look very much like the
ordinary foliage of the hazel-tree. Besides, they are thickly set with
small prickly hairs, which are extremely annoying to the fingers, and
must prove far more unpleasant to the delicate lips and noses of lower
animals. Just at present the nuts have reached this stage in our
copses; but as soon as autumn sets in, and the seeds are ripe, they
will turn brown, fall out of their withered investment, and easily
escape notice on the soil beneath, where the dead leaves will soon
cover them up in a mass of shrivelled brown, indistinguishable in shade
from the nuts themselves. Take, as an example of the more carefully
protected tropical kinds, the coco-nut. Growing on a very tall
palm-tree, it has to fall a considerable distance toward the earth; and
so it is wrapped round in a mass of loose knotted fibre, which breaks
the fall just as a lot of soft wool would do. Then, being a large nut,
fully stored with an abundance of meat, it offers special attractions
to animals, and consequently requires special means of defence.
Accordingly, its shell is extravagantly thick, only one small soft spot
being left at the blunter end, through which the young plant may push
its head. Once upon a time, to be sure, the coco-nut contained three
kernels, and had three such soft spots or holes; but now two of them
are aborted, and the two holes remain only in the form of hard scars.
The Brazil nut is even a better illustration. Probably few people know
that the irregular angular nuts which appear at dessert by that name
are originally contained inside a single round shell, where they fit
tightly together, and acquire their queer indefinite shapes by mutual
pressure. So the South American monkey has first to crack the thick
external common shell against a stone or otherwise; and, if he is
successful in this process, he must afterwards break the separate
sharp-edged inner nuts with his teeth--a performance which is always
painful and often ineffectual.
Yet it is curious that nuts and fruits are really produced by the very
slightest variations on a common type, so much so that the technical
botanist does not recognise the popular distinction between them at
all. In his eyes, the walnut and the coco-nut are not nuts, but
'drupaceous fruits,' just like the plum and the cherry. All four alike
contain a kernel within, a hard shell outside it, and a fibrous mass
outside that again, bounded by a thin external layer. Only, while in
the plum and cherry this fibrous mass becomes succulent and fills with
sugary juice, in the walnut its juice is bitter, and in the coco-nut it
has no juice at all, but remains a mere matted layer of dry fibres. And
while the thin external skin becomes purple in the plum and red in the
cherry as the fruits ripen, it remains green and brown in the walnut
and coco-nut all their time. Nevertheless, Darwinism shows us both here
and elsewhere that the popular distinction answers to a real difference
of origin and function. When a seed-vessel, whatever its botanical
structure, survives by dint of attracting animals, it always acquires a
bright-coloured envelope and a sweet pulp; while it usually possesses a
hard seed-shell, and often infuses bitter essences into its kernel. On
the other hand, when a seed-vessel survives by escaping the notice of
animals, it generally has a sweet and pleasant kernel, which it
protects by a hard shell and an inconspicuous and nauseous envelope. If
the kernel itself is bitter, as with the horse-chestnut, the need for
disguise and external protection is much lessened. But the best
illustration of all is seen in the West Indian cashew-nut, which is
what Alice in Wonderland would have called a portmanteau seed-vessel--a
fruit and a nut rolled into one. In this curious case, the stalk swells
out into a bright-coloured and juicy mass, looking something like a
pear, but of course containing no seeds; while the nut grows out from
its end, secured from intrusion by a covering with a pungent juice,
which burns and blisters the skin at a touch. No animal except man can
ever successfully tackle the cashew-nut itself; but by eating the
pear-like stalk other animals ultimately aid in distributing the seed.
The cashew thus vicariously sacrifices its fruit-stem for the sake of
preserving its nut.
All nature is a continuous game of cross-purposes. Animals perpetually
outwit plants, and plants in return once more outwit animals. Or, to
drop the metaphor, those animals alone survive which manage to get a
living in spite of the protections adopted by plants; and those plants
alone survive whose peculiarities happen successfully to defy the
attack of animals. There you have the Darwinian Iliad in a nutshell.
XVIII.
_A PRETTY LAND-SHELL._
The heavy rains which have done so much harm to the standing corn have
at least had the effect of making the country look greener and lovelier
than I have seen it look for many seasons. There is now a fresh verdure
about the upland pastures and pine woods which almost reminds one of
the deep valleys of the Bernese Oberland in early spring. Last year's
continuous wet weather gave the trees and grass a miserable draggled
appearance; but this summer's rain, coming after a dry spring, has
brought out all the foliage in unwonted luxuriance; and everybody
(except the British farmer) agrees that we have never seen the country
look more beautiful. Though the year is now so far advanced, the trees
are still as green as in springtide; and the meadows, with their rich
aftermath springing up apace, look almost as lush and fresh as they did
in early June. Londoners who get away to the country or the seaside
this month will enjoy an unexpected treat in seeing the fields as they
ought to be seen a couple of months sooner in the season.
Here, on the edge of the down, where I have come up to get a good
blowing from the clear south-west breeze, I have just sat down to rest
myself awhile and to admire the view, and have reverted for a moment to
my old habit of snail-hunting. Years ago, when evolution was an
infant--an infant much troubled by the complaints inseparable from
infancy, but still a sturdy and vigorous child, destined to outlive and
outgrow its early attacks--I used to collect slugs and snails, from an
evolutionist standpoint, and put their remains into a cabinet; and to
this day I seldom go out for a walk without a few pill-boxes in my
pocket, in case I should happen to hit upon any remarkable specimen.
Now here in the tall moss which straggles over an old heap of stones I
have this moment lighted upon a beautifully marked shell of our
prettiest English snail. How beautiful it is I could hardly make you
believe, unless I had you here and could show it to you; for most
people only know the two or three ugly brown or banded snails that prey
upon their cabbages and lettuces, and have no notion of the lovely
shells to be found by hunting among English copses and under the dead
leaves of Scotch hill-sides. This cyclostoma, however,--I _must_
trouble you with a Latin name for once--is so remarkably pretty, with
its graceful elongated spiral whorls, and its delicately chiselled
fretwork tracery, that even naturalists (who have perhaps, on the
whole, less sense of beauty than any class of men I know) have
recognised its loveliness by giving it the specific epithet of
_elegans_. It is big enough for anybody to notice it, being about the
size of a periwinkle; and its exquisite stippled chasing is strongly
marked enough to be perfectly visible to the naked eye. But besides its
beauty, the cyclostoma has a strong claim upon our attention because of
its curious history.
Long ago, in the infantile days of evolutionism, I often wondered why
people made collections on such an irrational plan. They always try to
get what they call the most typical specimens, and reject all those
which are doubtful or intermediate. Hence the dogma of the fixity of
species becomes all the more firmly settled in their minds, because
they never attend to the existing links which still so largely bridge
over the artificial gaps created by our nomenclature between kind and
kind. I went to work on the opposite plan, collecting all those
aberrant individuals which most diverged from the specific type. In
this way I managed to make some series so continuous that one might
pass over specimens of three or four different kinds, arranged in rows,
without ever being able to say quite clearly, by the eye alone, where
one group ended and the next group began. Among the snails such an
arrangement is peculiarly easy; for some of the species are very
indefinite, and the varieties are numerous under each species. Nothing
can give one so good a notion of the plasticity of organic forms as
such a method. The endless varieties and intermediate links which exist
amongst dogs is the nearest example to it with which ordinary observers
are familiar.