Transcriber's Note: Minor typographical errors have been corrected
without note. Irregularities and inconsistencies in the text have
been retained as printed. Words printed in italics are noted with
underscores: _italics_. Words printed in bold are noted with
tildes: ~bold~.
Dear Mother, take this English posy, culled.
In alien fields beyond the severing sea:
Take it in memory of the boy you lulled
One chill Canadian winter on your knee.
Its flowers are but chance friends of after years,
Whose very names my childhood hardly knew;
And even today far sweeter in my ears
Ring older names unheard long seasons through.
I loved them all--the bloodroot, waxen white,
Canopied mayflower, trilliums red and pale,
Flaunting lobelia, lilies richly dight,
And pipe-plant from the wood behind the Swale.
I knew each dell where yellow violets blow,
Each bud or leaf the changing seasons bring;
I marked each spot where from the melting snow
Peeped forth the first hepatica of spring.
I watched the fireflies on the shingly ridge
Beside the swamp that bounds the Baron's hill;
Or tempted sunfish by the ebbing bridge,
Or hooked a bass by Shirley Going's mill.
These were my budding fancy's mother-tongue:
But daisies, cowslips, dodder, primrose-hips,
All beasts or birds my little book has sung,
Sit like a borrowed speech on stammering lips.
And still I build fond dreams of happier days,
If hard-earned pence may bridge the ocean o'er;
That yet our boy may see my mother's face,
And gather shells beside Ontario's shore:
May yet behold Canadian woodlands dim,
And flowers and birds his father loved to see;
While you and I sit by and smile on him,
As down grey years you sat and smiled on me.
G. A.
_By the same Author._
PHYSIOLOGICAL ÆSTHETICS: a Scientific Theory of Beauty (London: C.
KEGAN PAUL & CO.)
THE COLOUR-SENSE: its Origin and Development. An Essay on Comparative
Psychology. (London: TRÜBNER & CO.)
THE EVOLUTIONIST AT LARGE
LONDON: PRINTED BY
SPOTTISWOODE AND CO., NEW-STREET SQUARE
AND PARLIAMENT STREET
THE EVOLUTIONIST AT LARGE
BY
GRANT ALLEN
London
CHATTO & WINDUS, PICCADILLY
1881
_All rights reserved_
PREFACE.
These Essays originally appeared in the columns of the 'St. James's
Gazette,' and I have to thank the courtesy of the Editor for kind
permission to republish them. My object in writing them was to make the
general principles and methods of evolutionists a little more familiar
to unscientific readers. Biologists usually deal with those underlying
points of structure which are most really important, and on which all
technical discussion must necessarily be based. But ordinary people
care little for such minute anatomical and physiological details. They
cannot be expected to interest themselves in the _flexor pollicis
longus_, or the _hippocampus major_ about whose very existence
they are ignorant, and whose names suggest to them nothing but
unpleasant ideas. What they want to find out is how the outward and
visible forms of plants and animals were produced. They would much
rather learn why birds have feathers than why they have a keeled
sternum; and they think the origin of bright flowers far more
attractive than the origin of monocotyledonous seeds or exogenous
stems. It is with these surface questions of obvious outward appearance
that I have attempted to deal in this little series. My plan is to take
a simple and well-known natural object, and give such an explanation as
evolutionary principles afford of its most striking external features.
A strawberry, a snail-shell, a tadpole, a bird, a wayside flower--these
are the sort of things which I have tried to explain. If I have not
gone very deep, I hope at least that I have suggested in simple
language the right way to go to work.
I must make an apology for the form in which the essays are cast, so
far as regards the apparent egotism of the first person. When they
appeared anonymously in the columns of a daily paper, this air of
personality was not so obtrusive: now that they reappear under my own
name, I fear it may prove somewhat too marked. Nevertheless, to cut out
the personal pronoun would be to destroy the whole machinery of the
work: so I have reluctantly decided to retain it, only begging the
reader to bear in mind that the _I_ of the essays is not a real
personage, but the singular number of the editorial _we_.
I have made a few alterations and corrections in some of the papers,
so as to bring the statements into closer accordance with scientific
accuracy. At the same time, I should like to add that I have
intentionally simplified the scientific facts as far as possible. Thus,
instead of saying that the groundsel is a composite, I have said that
it is a daisy by family; and instead of saying that the ascidian larva
belongs to the sub-kingdom Chordata, I have said that it is a first
cousin of the tadpole. For these simplifications, I hope technical
biologists will pardon me. After all, if you wish to be understood, it
is best to speak to people in words whose meanings they know. Definite
and accurate terminology is necessary to express definite and accurate
knowledge; but one may use vague expressions where the definite ones
would convey no ideas.
I have to thank the kindness of my friend the Rev. E. PURCELL, of
Lincoln College, Oxford, for the clever and appropriate design which
appears upon the cover.
G. A.
CONTENTS.
PAGE
A BALLADE OF EVOLUTION 1
I. MICROSCOPIC BRAINS 3
II. A WAYSIDE BERRY 16
III. IN SUMMER FIELDS 25
IV. A SPRIG OF WATER CROWFOOT 36
V. SLUGS AND SNAILS 48
VI. A STUDY OF BONES 59
VII. BLUE MUD 67
VIII. CUCKOO-PINT 77
IX. BERRIES AND BERRIES 87
X. DISTANT RELATIONS 96
XI. AMONG THE HEATHER 105
XII. SPECKLED TROUT 114
XIII. DODDER AND BROOMRAPE 124
XIV. DOG'S MERCURY AND PLANTAIN 133
XV. BUTTERFLY PSYCHOLOGY 142
XVI. BUTTERFLY ÆSTHETICS 153
XVII. THE ORIGIN OF WALNUTS 161
XVIII. A PRETTY LAND-SHELL 172
XIX. DOGS AND MASTERS 181
XX. BLACKCOCK 189
XXI. BINDWEED 198
XXII. ON CORNISH CLIFFS 207
_A BALLADE OF EVOLUTION._
In the mud of the Cambrian main
Did our earliest ancestor dive:
From a shapeless albuminous grain
We mortals our being derive.
He could split himself up into five,
Or roll himself round like a ball;
For the fittest will always survive,
While the weakliest go to the wall.
As an active ascidian again
Fresh forms he began to contrive,
Till he grew to a fish with a brain,
And brought forth a mammal alive.
With his rivals he next had to strive,
To woo him a mate and a thrall;
So the handsomest managed to wive,
While the ugliest went to the wall.
At length as an ape he was fain
The nuts of the forest to rive;
Till he took to the low-lying plain,
And proceeded his fellow to knive.
Thus did cannibal men first arrive,
One another to swallow and maul;
And the strongest continued to thrive,
While the weakliest went to the wall.
ENVOY.
Prince, in our civilised hive,
Now money's the measure of all;
And the wealthy in coaches can drive,
While the needier go to the wall.
THE EVOLUTIONIST AT LARGE.
I.
_MICROSCOPIC BRAINS._
Sitting on this little rounded boss of gneiss beside the path which
cuts obliquely through the meadow, I am engaged in watching a brigade
of ants out on foraging duty, and intent on securing for the nest three
whole segments of a deceased earthworm. They look for all the world
like those busy companies one sees in the Egyptian wall-paintings,
dragging home a huge granite colossus by sheer force of bone and sinew.
Every muscle in their tiny bodies is strained to the utmost as they
prise themselves laboriously against the great boulders which strew the
path, and which are known to our Brobdingnagian intelligence as grains
of sand. Besides the workers themselves, a whole battalion of
stragglers runs to and fro upon the broad line which leads to the
head-quarters of the community. The province of these stragglers, who
seem so busy doing nothing, probably consists in keeping communications
open, and encouraging the sturdy pullers by occasional relays of fresh
workmen. I often wish that I could for a while get inside those tiny
brains, and see, or rather smell, the world as ants do. For there can
be little doubt that to these brave little carnivores here the universe
is chiefly known as a collective bundle of odours, simultaneous or
consecutive. As our world is mainly a world of visible objects, theirs,
I believe, is mainly a world of olfactible things.
In the head of every one of these little creatures is something that we
may fairly call a brain. Of course most insects have no real brains;
the nerve-substance in their heads is a mere collection of ill-arranged
ganglia, directly connected with their organs of sense. Whatever man
may be, an earwig at least is a conscious, or rather a semi-conscious,
automaton. He has just a few knots of nerve-cells in his little pate,
each of which leads straight from his dim eye or his vague ear or
his indefinite organs of taste; and his muscles obey the promptings
of external sensations without possibility of hesitation or
consideration, as mechanically as the valve of a steam-engine obeys the
governor-balls. You may say of him truly, 'Nihil est in intellectu quod
non fuerit in sensu;' and you need not even add the Leibnitzian saving
clause, 'nisi ipse intellectus;' for the poor soul's intellect is
wholly deficient, and the senses alone make up all that there is of
him, subjectively considered. But it is not so with the highest
insects. They have something which truly answers to the real brain of
men, apes, and dogs, to the cerebral hemispheres and the cerebellum
which are superadded in us mammals upon the simple sense-centres of
lower creatures. Besides the eye, with its optic nerve and optic
perceptive organs--besides the ear, with its similar mechanism--we
mammalian lords of creation have a higher and more genuine brain, which
collects and compares the information given to the senses, and sends
down the appropriate messages to the muscles accordingly. Now, bees and
flies and ants have got much the same sort of arrangement, on a smaller
scale, within their tiny heads. On top of the little knots which do
duty as nerve-centres for their eyes and mouths, stand two stalked bits
of nervous matter, whose duty is analogous to that of our own brains.
And that is why these three sorts of insects think and reason so much
more intellectually than beetles or butterflies, and why the larger
part of them have organised their domestic arrangements on such an
excellent co-operative plan.
We know well enough what forms the main material of thought with bees
and flies, and that is visible objects. For you must think about
_something_ if you think at all; and you can hardly imagine a
contemplative blow-fly setting itself down to reflect, like a Hindu
devotee, on the syllable Om, or on the oneness of existence. Abstract
ideas are not likely to play a large part in apian consciousness. A bee
has a very perfect eye, and with this eye it can see not only form, but
also colour, as Sir John Lubbock's experiments have shown us. The
information which it gets through its eye, coupled with other ideas
derived from touch, smell, and taste, no doubt makes up the main
thinkable and knowable universe as it reveals itself to the apian
intelligence. To ourselves and to bees alike the world is, on the
whole, a coloured picture, with the notions of distance and solidity
thrown in by touch and muscular effort; but sight undoubtedly plays the
first part in forming our total conception of things generally.
What, however, forms the thinkable universe of these little ants
running to and fro so eagerly at my feet? That is a question which used
long to puzzle me in my afternoon walks. The ant has a brain and an
intelligence, but that brain and that intelligence must have been
developed out of _something_. _Ex nihilo nihil fit._ You cannot think
and know if you have nothing to think about. The intelligence of the
bee and the fly was evolved in the course of their flying about and
looking at things: the more they flew, and the more they saw, the more
they knew; and the more brain they got to think with. But the ant does
not generally fly, and, as with most comparatively unlocomotive
animals, its sight is bad. True, the winged males and females have
retained in part the usual sharp eyes of their class--for they are
first cousins to the bees--and they also possess three little eyelets
or _ocelli_, which are wanting to the wingless neuters. Without these
they would never have found one another in their courtship, and they
would have run their heads against the nearest tree, or rushed down the
gaping throat of the first expectant swallow, and so effectually
extinguished their race. Flying animals cannot do without eyes, and
they always possess the most highly developed vision of any living
creatures. But the wingless neuters are almost blind--in some species
quite so; and Sir John Lubbock has shown that their appreciation of
colour is mostly confined to an aversion to red light, and a
comparative endurance of blue. Moreover, they are apparently deaf, and
most of their other senses seem little developed. What can be the raw
material on which that pin's head of a brain sets itself working? For,
small as it is, it is a wonderful organ of intellect; and though Sir
John Lubbock has shown us all too decisively that the originality and
inventive genius of ants have been sadly overrated by Solomon and
others, yet Darwin is probably right none the less in saying that no
more marvellous atom of matter exists in the universe than this same
wee lump of microscopic nerve substance.
My dog Grip, running about on the path there, with his nose to the
ground, and sniffing at every stick and stone he meets on his way,
gives us the clue to solve the problem. Grip, as Professor Croom
Robertson suggests, seems capable of extracting a separate and
distinguishable smell from everything. I have only to shy a stone on
the beach among a thousand other stones, and my dog, like a well-bred
retriever as he is, selects and brings back to me that individual stone
from all the stones around, by exercise of his nose alone. It is plain
that Grip's world is not merely a world of sights, but a world of
smells as well. He not only smells smells, but he remembers smells, he
thinks smells, he even dreams smells, as you may see by his sniffing
and growling in his sleep. Now, if I were to cut open Grip's head
(which heaven forfend), I should find in it a correspondingly big
smell-nerve and smell-centre--an olfactory lobe, as the anatomists say.
All the accumulated nasal experiences of his ancestors have made that
lobe enormously developed. But in a man's head you would find a very
large and fine optic centre, and only a mere shrivelled relic to
represent the olfactory lobes. You and I and our ancestors have had but
little occasion for sniffing and scenting; our sight and our touch have
done duty as chief intelligencers from the outer world; and the nerves
of smell, with their connected centres, have withered away to the
degenerate condition in which they now are. Consequently, smell plays
but a small part in our thought and our memories. The world that we
know is chiefly a world of sights and touches. But in the brain of dog,
or deer, or antelope, smell is a prevailing faculty; it colours all
their ideas, and it has innumerable nervous connections with every part
of their brain. The big olfactory lobes are in direct communication
with a thousand other nerves; odours rouse trains of thought or
powerful emotions in their minds just as visible objects do in our own.
Now, in the dog or the horse sight and smell are equally developed; so
that they probably think of most things about equally in terms of each.
In ourselves, sight is highly developed, and smell is a mere relic; so
that we think of most things in terms of sight alone, and only rarely,
as with a rose or a lily, in terms of both. But in ants, on the
contrary, smell is highly developed and sight a mere relic; so that
they probably think of most things as smellable only, and very little
as visible in form or colour. Dr. Bastian has shown that bees and
butterflies are largely guided by scent; and though he is certainly
wrong in supposing that sight has little to do with leading them to
flowers (for if you cut off the bright-coloured corolla they will never
discover the mutilated blossoms, even when they visit others on the
same plant), yet the mere fact that so many flowers are scented is by
itself enough to show that perfume has a great deal to do with the
matter. In wingless ants, while the eyes have undergone degeneration,
this high sense of smell has been continued and further developed, till
it has become their principal sense-endowment, and the chief raw
material of their intelligence. Their active little brains are almost
wholly engaged in correlating and co-ordinating smells with actions.
Their olfactory nerves give them nearly all the information they can
gain about the external world, and their brains take in this
information and work out the proper movements which it indicates. By
smell they find their way about and carry on the business of their
lives. Just as you and I know the road from Regent's Circus to Pall
Mall by visible signs of the street-corners and the Duke of York's
Column, so these little ants know the way from the nest to the corpse
of the dismembered worm by observing and remembering the smells which
they met with on their way. See: I obliterate the track for an inch or
two with my stick, and the little creatures go beside themselves with
astonishment and dismay. They rush about wildly, inquiring of one
another with their antennæ whether this is really Doomsday, and whether
the whole course of nature has been suddenly revolutionised. Then,
after a short consultation, they determine upon action; and every ant
starts off in a different direction to hunt the lost track, head to the
ground, exactly as a pointer hunts the missing trail of a bird or hare.
Each ventures an inch or so off, and then runs back to find the rest,
for fear he should get isolated altogether. At last, after many
failures, one lucky fellow hits upon the well-remembered train of
scents, and rushes back leaving smell-tracks no doubt upon the soil
behind him. The message goes quickly round from post to post, each
sentry making passes with his antennæ to the next picket, and so
sending on the news to the main body in the rear. Within five minutes
communications are re-established, and the precious bit of worm-meat
continues triumphantly on its way along the recovered path. An
ingenious writer would even have us believe that ants possess a
scent-language of their own, and emit various odours from their antennæ
which the other ants perceive with theirs, and recognise as distinct in
meaning. Be this as it may, you cannot doubt, if you watch them long,
that scents and scents alone form the chief means by which they
recollect and know one another, or the external objects with which they
come in contact. The whole universe is clearly to them a complicated
picture made up entirely of infinite interfusing smells.
II.
_A WAYSIDE BERRY._
Half-hidden in the luxuriant growth of leaves and flowers that drape
the deep side of this green lane, I have just espied a little picture
in miniature, a tall wild strawberry-stalk with three full red berries
standing out on its graceful branchlets. There are glossy
hart's-tongues on the matted bank, and yellow hawkweeds, and bright
bunches of red campion; but somehow, amid all that wealth of shape and
colour, my eye falls and rests instinctively upon the three little
ruddy berries, and upon nothing else. I pick the single stalk from the
bank and hold it here in my hands. The origin and development of these
pretty bits of red pulp is one of the many curious questions upon which
modern theories of life have cast such a sudden and unexpected flood of
light. What makes the strawberry stalk grow out into this odd and
brightly coloured lump, bearing its small fruits embedded on its
swollen surface? Clearly the agency of those same small birds who have
been mainly instrumental in dressing the haw in its scarlet coat, and
clothing the spindle-berries with their two-fold covering of crimson
doublet and orange cloak.
In common language we speak of each single strawberry as a fruit. But
it is in reality a collection of separate fruits, the tiny yellow-brown
grains which stud its sides being each of them an individual little
nut; while the sweet pulp is, in fact, no part of the true fruit at
all, but merely a swollen stalk. There is a white potentilla so like a
strawberry blossom that even a botanist must look closely at the plant
before he can be sure of its identity. While they are in flower the two
heads remain almost indistinguishable; but when the seed begins to set
the potentilla develops only a collection of dry fruitlets, seated upon
a green receptacle, the bed or soft expansion which hangs on to the
'hull' or calyx. Each fruitlet consists of a thin covering, enclosing a
solitary seed. You may compare one of them separately to a plum, with
its single kernel, only that in the plum the covering is thick and
juicy, while in the potentilla and the fruitlets of the strawberry it
is thin and dry. An almond comes still nearer to the mark. Now the
potentilla shows us, as it were, the primitive form of the strawberry.
But in the developed ripe strawberry as we now find it the fruitlets
are not crowded upon a green receptacle. After flowering, the
strawberry receptacle lengthens and broadens, so as to form a roundish
mass of succulent pulp; and as the fruitlets approach maturity this
sour green pulp becomes soft, sweet, and red. The little seed-like
fruits, which are the important organs, stand out upon its surface like
mere specks; while the comparatively unimportant receptacle is all that
we usually think of when we talk about strawberries. After our usual
Protagorean fashion we regard man as the measure of all things, and pay
little heed to any part of the compound fruit-cluster save that which
ministers directly to our own tastes.
But why does the strawberry develop this large mass of apparently
useless matter? Simply in order the better to ensure the dispersion of
its small brown fruitlets. Birds are always hunting for seeds and
insects along the hedge-rows, and devouring such among them as contain
any available foodstuff. In most cases they crush the seeds to pieces
with their gizzards, and digest and assimilate their contents. Seeds of
this class are generally enclosed in green or brown capsules, which
often escape the notice of the birds, and so succeed in perpetuating
their species. But there is another class of plants whose members
possess hard and indigestible seeds, and so turn the greedy birds from
dangerous enemies into useful allies. Supposing there was by chance,
ages ago, one of these primitive ancestral strawberries, whose
receptacle was a little more pulpy than usual, and contained a small
quantity of sugary matter, such as is often found in various parts of
plants; then it might happen to attract the attention of some hungry
bird, which, by eating the soft pulp, would help in dispersing the
indigestible fruitlets. As these fruitlets sprang up into healthy young
plants, they would tend to reproduce the peculiarity in the structure
of the receptacle which marked the parent stock, and some of them would
probably display it in a more marked degree. These would be sure to get
eaten in their turn, and so to become the originators of a still more
pronounced strawberry type. As time went on, the largest and sweetest
berries would constantly be chosen by the birds, till the whole species
began to assume its existing character. The receptacle would become
softer and sweeter, and the fruits themselves harder and more
indigestible: because, on the one hand, all sour or hard berries would
stand a poorer chance of getting dispersed in good situations for their
growth, while, on the other hand, all soft-shelled fruitlets would be
ground up and digested by the bird, and thus effectually prevented from
ever growing into future plants. Just in like manner, many tropical
nuts have extravagantly hard shells, as only those survive which can
successfully defy the teeth and hands of the clever and persistent
monkey.
This accounts for the strawberry being sweet and pulpy, but not for its
being red. Here, however, a similar reason comes into play. All
ripening fruits and opening flowers have a natural tendency to grow
bright red, or purple, or blue, though in many of them the tendency is
repressed by the dangers attending brilliant displays of colour. This
natural habit depends upon the oxidation of their tissues, and is
exactly analogous to the assumption of autumn tints by leaves. If a
plant, or part of a plant, is injured by such a change of colour,
through being rendered more conspicuous to its foes, it soon loses the
tendency under the influence of natural selection; in other words,
those individuals which most display it get killed out, while those
which least display it survive and thrive. On the other hand, if
conspicuousness is an advantage to the plant, the exact opposite
happens, and the tendency becomes developed into a confirmed habit.
This is the case with the strawberry, as with many other fruits. The
more bright-coloured the berry is, the better its chance of getting its
fruitlets dispersed. Birds have quick eyes for colour, especially for
red and white; and therefore almost all edible berries have assumed one
or other of these two hues. So long as the fruitlets remain unripe, and
would therefore be injured by being eaten, the pulp remains sour,
green, and hard; but as soon as they have become fit for dispersion it
grows soft, fills with sugary juice, and acquires its ruddy outer
flesh. Then the birds see and recognise it as edible, and govern
themselves accordingly.
But if this is the genesis of the strawberry, asks somebody, why have
not all the potentillas and the whole strawberry tribe also become
berries of the same type? Why are there still potentilla fruit-clusters
which consist of groups of dry seed-like nuts? Ay, there's the rub.
Science cannot answer as yet. After all, these questions are still in
their infancy, and we can scarcely yet do more than discover a single
stray interpretation here and there. In the present case a botanist can
only suggest either that the potentilla finds its own mode of
dispersion equally well adapted to its own peculiar circumstances, or
else that the lucky accident, the casual combination of circumstances,
which produced the first elongation of the receptacle in the strawberry
has never happened to befall its more modest kinsfolk. For on such
occasional freaks of nature the whole evolution of new varieties
entirely depends. A gardener may raise a thousand seedlings, and only
one or none among them may present a single new and important feature.
So a species may wait for a thousand years, or for ever, before its
circumstances happen to produce the first step towards some desirable
improvement. One extra petal may be invaluable to a five-rayed flower
as effecting some immense saving of pollen in its fertilisation; and
yet the 'sport' which shall give it this sixth ray may never occur, or
may be trodden down in the mire and destroyed by a passing cow.
III.
_IN SUMMER FIELDS._
Grip and I have come out for a morning stroll among the close-cropped
pastures beside the beck, in the very centre of our green little
dingle. Here I can sit, as is my wont, on a dry knoll, and watch the
birds, beasts, insects, and herbs of the field, while Grip scours the
place in every direction, intent, no doubt, upon those more practical
objects--mostly rats, I fancy--which possess a congenial interest for
the canine intelligence. From my coign of vantage on the knoll I can
take care that he inflicts no grievous bodily injury upon the sheep,
and that he receives none from the quick-tempered cow with the
brass-knobbed horns. For a kind of ancestral feud seems to smoulder for
ever between Grip and the whole race of kine, breaking out every now
and then into open warfare, which calls for my prompt interference, in
an attitude of armed but benevolent neutrality, merely for the friendly
purpose of keeping the peace.
This ancient feud, I imagine, is really ancestral, and dates many ages
further back in time than Grip's individual experiences. Cows hate dogs
instinctively, from their earliest calfhood upward. I used to doubt
once upon a time whether the hatred was not of artificial origin and
wholly induced by the inveterate human habit of egging on every dog to
worry every other animal that comes in its way. But I tried a mild
experiment one day by putting a half-grown town-bred puppy into a small
enclosure with some hitherto unworried calves, and they all turned to
make a common headway against the intruder with the same striking
unanimity as the most ancient and experienced cows. Hence I am inclined
to suspect that the antipathy does actually result from a vaguely
inherited instinct derived from the days when the ancestor of our kine
was a wild bull, and the ancestor of our dogs a wolf, on the wide
forest-clad plains of Central Europe. When a cow puts up its tail at
sight of a dog entering its paddock at the present day, it has probably
some dim instinctive consciousness that it stands in the presence of a
dangerous hereditary foe; and as the wolves could only seize with
safety a single isolated wild bull, so the cows now usually make common
cause against the intruding dog, turning their heads in one direction
with very unwonted unanimity, till his tail finally disappears under
the opposite gate. Such inherited antipathies seem common and natural
enough. Every species knows and dreads the ordinary enemies of its
race. Mice scamper away from the very smell of a cat. Young chickens
run to the shelter of their mother's wings when the shadow of a hawk
passes over their heads. Mr. Darwin put a small snake into a paper bag,
which he gave to the monkeys at the Zoo; and one monkey after another
opened the bag, looked in upon the deadly foe of the quadrumanous kind,
and promptly dropped the whole package with every gesture of horror and
dismay. Even man himself--though his instincts have all weakened so
greatly with the growth of his more plastic intelligence, adapted to a
wider and more modifiable set of external circumstances--seems to
retain a vague and original terror of the serpentine form.
If we think of parallel cases, it is not curious that animals should
thus instinctively recognise their natural enemies. We are not
surprised that they recognise their own fellows: and yet they must do
so by means of some equally strange automatic and inherited mechanism
in their nervous system. One butterfly can tell its mates at once from
a thousand other species, though it may differ from some of them only
by a single spot or line, which would escape the notice of all but the
most attentive observers. Must we not conclude that there are elements
in the butterfly's feeble brain exactly answering to the blank picture
of its specific type? So, too, must we not suppose that in every race
of animals there arises a perceptive structure specially adapted to the
recognition of its own kind? Babies notice human faces long before they
notice any other living thing. In like manner we know that most
creatures can judge instinctively of their proper food. One young bird
just fledged naturally pecks at red berries; another exhibits an
untaught desire to chase down grasshoppers; a third, which happens to
be born an owl, turns at once to the congenial pursuit of small
sparrows, mice, and frogs. Each species seems to have certain faculties
so arranged that the sight of certain external objects, frequently
connected with food in their ancestral experience, immediately arouses
in them the appropriate actions for its capture. Mr. Douglas Spalding
found that newly-hatched chickens darted rapidly and accurately at
flies on the wing. When we recollect that even so late an acquisition
as articulate speech in human beings has its special physical seat in
the brain, it is not astonishing that complicated mechanisms should
have arisen among animals for the due perception of mates, food, and
foes respectively. Thus, doubtless, the serpent form has imprinted
itself indelibly on the senses of monkeys, and the wolf or dog form on
those of cows: so that even with a young ape or calf the sight of these
their ancestral enemies at once calls up uneasy or terrified feelings
in their half-developed minds. Our own infants in arms have no personal
experience of the real meaning to be attached to angry tones, yet they
shrink from the sound of a gruff voice even before they have learned to
distinguish their nurse's face.
When Grip gets among the sheep, their hereditary traits come out in a
very different manner. They are by nature and descent timid mountain
animals, and they have never been accustomed to face a foe, as cows and
buffaloes are wont to do, especially when in a herd together. You
cannot see many traces of the original mountain life among sheep, and
yet there are still a few remaining to mark their real pedigree. Mr.
Herbert Spencer has noticed the fondness of lambs for frisking on a
hillock, however small; and when I come to my little knoll here, I
generally find it occupied by a couple, who rush away on my approach,
but take their stand instead on the merest ant-hill which they can find
in the field. I once knew three young goats, kids of a mountain breed,
and the only elevated object in the paddock where they were kept was a
single old elm stump. For the possession of this stump the goats fought
incessantly; and the victor would proudly perch himself on the top,
with all four legs inclined inward (for the whole diameter of the tree
was but some fifteen inches), maintaining himself in his place with the
greatest difficulty, and butting at his two brothers until at last he
lost his balance and fell. This one old stump was the sole
representative in their limited experience of the rocky pinnacle upon
which their forefathers kept watch like sentinels; and their
instinctive yearnings prompted them to perch themselves upon the only
available memento of their native haunts. Thus, too, but in a dimmer
and vaguer way, the sheep, especially during his younger days, loves to
revert, so far as his small opportunities permit him, to the
unconsciously remembered habits of his race. But in mountain countries,
every one must have noticed how the sheep at once becomes a different
being. On the Welsh hills he casts away all the dull and heavy serenity
of his brethren on the South Downs, and displays once more the freedom,
and even the comparative boldness, of a mountain breed. A
Merionethshire ewe thinks nothing of running up one side of a
low-roofed barn and down the other, or of clearing a stone wall which a
Leicestershire farmer would consider extravagantly high.
Another mountain trait in the stereotyped character of sheep is their
well-known sequaciousness. When Grip runs after them they all run away
together: if one goes through a certain gap in the hedge, every other
follows; and if the leader jumps the beck at a certain spot, every lamb
in the flock jumps in the self-same place. It is said that if you hold
a stick for the first sheep to leap over, and then withdraw it, all the
succeeding sheep will leap with mathematical accuracy at the
corresponding point; and this habit is usually held up to ridicule as
proving the utter stupidity of the whole race. It really proves nothing
but the goodness of their ancestral instincts. For mountain animals,
accustomed to follow a leader, that leader being the bravest and
strongest ram of the flock, must necessarily follow him with the most
implicit obedience. He alone can see what obstacles come in the way;
and each of the succeeding train must watch and imitate the actions of
their predecessors. Otherwise, if the flock happens to come to a chasm,
running as they often must with some speed, any individual which
stopped to look and decide for itself before leaping would inevitably
be pushed over the edge by those behind it, and so would lose all
chance of handing down its cautious and sceptical spirit to any
possible descendants. On the other hand, those uninquiring and blindly
obedient animals which simply did as they saw others do would both
survive themselves and become the parents of future and similar
generations. Thus there would be handed down from dam to lamb a general
tendency to sequaciousness--a follow-my-leader spirit, which was really
the best safeguard for the race against the evils of insubordination,
still so fatal to Alpine climbers. And now that our sheep have settled
down to a tame and monotonous existence on the downs of Sussex or the
levels of the Midlands, the old instinct clings to them still, and
speaks out plainly for their mountain origin. There are few things in
nature more interesting to notice than these constant survivals of
instinctive habits in altered circumstances. They are to the mental
life what rudimentary organs are to the bodily structure: they remind
us of an older order of things, just as the abortive legs of the
blind-worm show us that he was once a lizard, and the hidden shell of
the slug that he was once a snail.
IV.
_A SPRIG OF WATER CROWFOOT._
The little streamlet whose tiny ranges and stickles form the middle
thread of this green combe in the Dorset downs is just at present
richly clad with varied foliage. Tall spikes of the yellow flag rise
above the slow-flowing pools, while purple loose-strife overhangs the
bank, and bunches of the arrowhead stand high out of their watery home,
just unfolding their pretty waxen white flowers to the air. In the
rapids, on the other hand, I find the curious water crowfoot, a spray
of which I have this moment pulled out of the stream and am now holding
in my hand as I sit on the little stone bridge, with my legs dangling
over the pool below, known to me as the undoubted residence of a pair
of trout. It is a queer plant, this crowfoot, with its two distinct
types of leaves, much cleft below and broad above; and I often wonder
why so strange a phenomenon has attracted such very scant attention.
But then we knew so little of life in any form till the day before
yesterday that perhaps it is not surprising we should still have left
so many odd problems quite untouched.
This problem of the shape of leaves certainly seems to me a most
important one; and yet it has hardly been even recognised by our
scientific pastors and masters. At best, Mr. Herbert Spencer devotes to
it a passing short chapter, or Mr. Darwin a stray sentence. The
practice of classifying plants mainly by means of their flowers has
given the flower a wholly factitious and overwrought importance.
Besides, flowers are so pretty, and we cultivate them so largely, with
little regard to the leaves, that they have come to usurp almost the
entire interest of botanists and horticulturists alike. Darwinism
itself has only heightened this exclusive interest by calling attention
to the reciprocal relations which exist between the honey-bearing
blossom and the fertilising insect, the bright-coloured petals and the
myriad facets of the butterfly's eye. Yet the leaf is after all the
real plant, and the flower is but a sort of afterthought, an embryo
colony set apart for the propagation of like plants in future. Each
leaf is in truth a separate individual organism, united with many
others into a compound community, but possessing in full its own mouths
and digestive organs, and carrying on its own life to a great extent
independently of the rest. It may die without detriment to them; it may
be lopped off with a few others as a cutting, and it continues its
life-cycle quite unconcerned. An oak tree in full foliage is a
magnificent group of such separate individuals--a whole nation in
miniature: it may be compared to a branched coral polypedom covered
with a thousand little insect workers, while each leaf answers rather
to the separate polypes themselves. The leaves are even capable of
producing new individuals by what they contribute to the buds on every
branch; and the seeds which the tree as a whole produces are to be
looked upon rather as the founders of fresh colonies, like the swarms
of bees, than as fresh individuals alone. Every plant community, in
short, both adds new members to its own commonwealth, and sends off
totally distinct germs to form new commonwealths elsewhere. Thus the
leaf is, in truth, the central reality of the whole plant, while the
flower exists only for the sake of sending out a shipload of young
emigrants every now and then to try their fortunes in some unknown
soil.
The whole life-business of a leaf is, of course, to eat and grow, just
as these same functions form the whole life-business of a caterpillar
or a tadpole. But the way a plant eats, we all know, is by taking
carbon and hydrogen from air and water under the influence of sunlight,
and building them up into appropriate compounds in its own body.
Certain little green worms or convoluta have the same habit, and live
for the most part cheaply off sunlight, making starch out of carbonic
acid and water by means of their enclosed chlorophyll, exactly as if
they were leaves. Now, as this is what a leaf has to do, its form will
almost entirely depend upon the way it is affected by sunlight and the
elements around it--except, indeed, in so far as it may be called upon
to perform other functions, such as those of defence or defiance. This
crowfoot is a good example of the results produced by such agents. Its
lower leaves, which grow under water, are minutely subdivided into
little branching lance-like segments; while its upper ones, which raise
their heads above the surface, are broad and united, like the common
crowfoot type. How am I to account for these peculiarities? I fancy
somehow thus:--
Plants which live habitually under water almost always have thin, long,
pointed leaves, often thread-like or mere waving filaments. The reason
for this is plain enough. Gases are not very abundant in water, as it
only holds in solution a limited quantity of oxygen and carbonic acid.
Both of these the plant needs, though in varying quantities: the carbon
to build up its starch, and the oxygen to use up in its growth.
Accordingly, broad and large leaves would starve under water: there is
not material enough diffused through it for them to make a living from.
But small, long, waving leaves which can move up and down in the stream
would manage to catch almost every passing particle of gaseous matter,
and to utilise it under the influence of sunlight. Hence all plants
which live in fresh water, and especially all plants of higher rank,
have necessarily acquired such a type of leaf. It is the only form in
which growth can possibly take place under their circumstances. Of
course, however, the particular pattern of leaf depends largely upon
the ancestral form. Thus this crowfoot, even in its submerged leaves,
preserves the general arrangement of ribs and leaflets common to the
whole buttercup tribe. For the crowfoot family is a large and eminently
adaptable race. Some of them are larkspurs and similar queerly-shaped
blossoms; others are columbines which hang their complicated bells on
dry and rocky hillsides; but the larger part are buttercups or marsh
marigolds which have simple cup-shaped flowers, and mostly frequent low
and marshy ground. One of these typical crowfoots under stress of
circumstances--inundation, or the like--took once upon a time to living
pretty permanently in the water. As its native meadows grew deeper and
deeper in flood it managed from year to year to assume a more nautical
life. So, while its leaf necessarily remained in general structure a
true crowfoot leaf, it was naturally compelled to split itself up into
thinner and narrower segments, each of which grew out in the direction
where it could find most stray carbon atoms, and most sunlight, without
interference from its neighbours. This, I take it, was the origin of
the much-divided lower leaves.
But a crowfoot could never live permanently under water. Seaweeds and
their like, which propagate by a kind of spores, may remain below the
surface for ever; but flowering plants for the most part must come up
to the open air to blossom. The sea-weeds are in the same position as
fish, originally developed in the water and wholly adapted to it,
whereas flowering plants are rather analogous to seals and whales,
air-breathing creatures, whose ancestors lived on land, and who can
themselves manage an aquatic existence only by frequent visits to the
surface. So some flowering water-plants actually detach their male
blossoms altogether, and let them float loose on the top of the water;
while they send up their female flowers by means of a spiral coil, and
draw them down again as soon as the wind or the fertilising insects
have carried the pollen to its proper receptacle, so as to ripen their
seeds at leisure beneath the pond. Similarly, you may see the arrowhead
and the water-lilies sending up their buds to open freely in the air,
or loll at ease upon the surface of the stream. Thus the crowfoot, too,
cannot blossom to any purpose below the water; and as such among its
ancestors as at first tried to do so must of course have failed in
producing any seed, they and their kind have died out for ever; while
only those lucky individuals whose chance lot it was to grow a little
taller and weedier than the rest, and so overtop the stream, have
handed down their race to our own time.
But as soon as the crowfoot finds itself above the level of the river,
all the causes which made its leaf like those of other aquatic plants
have ceased to operate. The new leaves which sprout in the air meet
with abundance of carbon and sunlight on every side; and we know that
plants grow fast just in proportion to the supply of carbon. They have
pushed their way into an unoccupied field, and they may thrive apace
without let or hindrance. So, instead of splitting up into little
lance-like leaflets, they loll on the surface, and spread out broader
and fuller, like the rest of their race. The leaf becomes at once a
broad type of crowfoot leaf. Even the ends of the submerged leaves,
when any fall of the water in time of drought raises them above the
level, have a tendency (as I have often noticed) to grow broader and
fatter, with increased facilities for food; but when the whole leaf
rises from the first to the top the inherited family instinct finds
full play for its genius, and the blades fill out as naturally as
well-bred pigs. The two types of leaf remind one much of gills and
lungs respectively.
But above water, as below it, the crowfoot remains in principle a
crowfoot still. The traditions of its race, acquired in damp marshy
meadows, not actually under water, cling to it yet in spite of every
change. Born river and pond plants which rise to the surface, like the
water-lily or the duck-weed, have broad floating leaves that contrast
strongly with the waving filaments of wholly submerged species. They
can find plenty of food everywhere, and as the sunlight falls flat upon
them, they may as well spread out flat to catch the sunlight. No other
elbowing plants overtop them and appropriate the rays, so compelling
them to run up a useless waste of stem in order to pocket their fair
share of the golden flood. Moreover, they thus save the needless
expense of a stout leaf-stalk, as the water supports their lolling
leaves and blossoms; while the broad shade which they cast on the
bottom below prevents the undue competition of other species. But the
crowfoot, being by descent a kind of buttercup, has taken to the water
for a few hundred generations only, while the water-lily's ancestors
have been to the manner born for millions of years; and therefore it
happens that the crowfoot is at heart but a meadow buttercup still. One
glance at its simple little flower will show you that in a moment.
V.
_SLUGS AND SNAILS._