Darwiniana
by
Thomas Henry Huxley
Part 1 out of 6
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Thomas Henry Huxley
Collected Essays
(1893-1894)
Vol. II
Darwiniana
(Edition: published in 1893)
PREFACE
I have entitled this volume "Darwiniana" because the pieces republished in
it either treat of the ancient doctrine of Evolution, rehabilitated and
placed upon a sound scientific foundation, since and in consequence of, the
publication of the "Origin of Species;" or they attempt to meet the more
weighty of the unsparing criticisms with which that great work was visited
for several years after its appearance; or they record the impression left
by the personality of Mr. Darwin on one who had the privilege and the
happiness of enjoying his friendship for some thirty years; or they
endeavour to sum up his work and indicate its enduring influence on the
course of scientific thought.
Those who take the trouble to read the first two essays, published in 1859
and 1860, will, I think, do me the justice to admit that my zeal to secure
fair play for Mr. Darwin, did not drive me into the position of a mere
advocate; and that, while doing justice to the greatness of the argument I
did not fail to indicate its weak points. I have never seen any reason for
departing from the position which I took up in these two essays; and the
assertion which I sometimes meet with nowadays, that I have "recanted" or
changed my opinions about Mr. Darwin's views, is quite unintelligible to
me.
As I have said in the seventh essay, the fact of evolution is to my mind
sufficiently evidenced by palaeontology; and I remain of the opinion
expressed in the second, that until selective breeding is definitely proved
to give rise to varieties infertile with one another, the logical
foundation of the theory of natural selection is incomplete. We still
remain very much in the dark about the causes of variation; the apparent
inheritance of acquired characters in some cases; and the struggle for
existence within the organism, which probably lies at the bottom of both of
these phenomena.
Some apology is due to the reader for the reproduction of the "Lectures to
Working Men" in their original state. They were taken down in shorthand by
Mr. J. Aldous Mays, who requested me to allow him to print them. I was very
much pressed with work at the time; and, as I could not revise the reports,
which I imagined, moreover, would be of little or no interest to any but my
auditors, I stipulated that a notice should be prefixed to that effect.
This was done; but it did not prevent a considerable diffusion of the
little book in this country and in the United States, nor its translation
into more than one foreign language. Moreover Mr. Darwin often urged me to
revise and expand the lectures into a systematic popular exposition of the
topics of which they treat. I have more than once set about the task: but
the proverb about spoiling a horn and not making a spoon, is particularly
applicable to attempts to remodel a piece of work which may have served its
immediate purpose well enough.
So I have reprinted the lectures as they stand, with all their
imperfections on their heads. It would seem that many people must have
found them useful thirty years ago; and, though the sixties appear now to
be reckoned by many of the rising generation as a part of the dark ages, I
am not without some grounds for suspecting that there yet remains a fair
sprinkling even of "philosophic thinkers" to whom it may be a profitable,
perhaps even a novel, task to descend from the heights of speculation and
go over the A B C of the great biological problem as it was set before a
body of shrewd artisans at that remote epoch.
T. H. H.
Hodeslea, Eastbourne, _April 7th_, 1893.
CONTENTS
I THE DARWINIAN HYPOTHESIS [1859]
II THE ORIGIN OF SPECIES [1860]
III CRITICISM ON "THE ORIGIN OF SPECIES" [1864]
IV THE GENEALOGY OF ANIMALS [1869]
V MR. DARWIN'S CRITICS [1871]
VI EVOLUTION IN BIOLOGY [1878]
VII THE COMING OF AGE OF "THE ORIGIN OF SPECIES" [1880]
VIII CHARLES DARWIN [1882]
IX THE DARWIN MEMORIAL [1885]
X OBITUARY [1888]
XI SIX LECTURES TO WORKING MEN "ON OUR KNOWLEDGE OF THE CAUSES OF THE
PHENOMENA OF ORGANIC NATURE" [1863]
I
THE DARWINIAN HYPOTHESIS
[1859]
The hypothesis of which the present work of Mr. Darwin is but the
preliminary outline, may be stated in his own language as follows:--
"Species originated by means of natural selection, or through the
preservation of the favoured races in the struggle for life." To render
this thesis intelligible, it is necessary to interpret its terms. In the
first place, what is a species? The question is a simple one, but the right
answer to it is hard to find, even if we appeal to those who should know
most about it. It is all those animals or plants which have descended from
a single pair of parents; it is the smallest distinctly definable group of
living organisms; it is an eternal and immutable entity; it is a mere
abstraction of the human intellect having no existence in nature. Such are
a few of the significations attached to this simple word which may be
culled from authoritative sources; and if, leaving terms and theoretical
subtleties aside, we turn to facts and endeavour to gather a meaning for
ourselves, by studying the things to which, in practice, the name of
species is applied, it profits us little. For practice varies as much as
theory. Let two botanists or two zoologists examine and describe the
productions of a country, and one will pretty certainly disagree with the
other as to the number, limits, and definitions of the species into which
he groups the very same things. In these islands, we are in the habit of
regarding mankind as of one species, but a fortnight's steam will land us
in a country where divines and savants, for once in agreement, vie with one
another in loudness of assertion, if not in cogency of proof, that men are
of different species; and, more particularly, that the species negro is so
distinct from our own that the Ten Commandments have actually no reference
to him. Even in the calm region of entomology, where, if anywhere in this
sinful world, passion and prejudice should fail to stir the mind, one
learned coleopterist will fill ten attractive volumes with descriptions of
species of beetles, nine-tenths of which are immediately declared by his
brother beetle-mongers to be no species at all.
The truth is that the number of distinguishable living creatures almost
surpasses imagination. At least 100,000 such kinds of insects alone have
been described and may be identified in collections, and the number of
separable kinds of living things is under-estimated at half a million.
Seeing that most of these obvious kinds have their accidental varieties,
and that they often shade into others by imperceptible degrees, it may well
be imagined that the task of distinguishing between what is permanent and
what fleeting, what is a species and what a mere variety, is sufficiently
formidable.
But is it not possible to apply a test whereby a true species may be known
from a mere variety? Is there no criterion of species? Great authorities
affirm that there is--that the unions of members of the same species are
always fertile, while those of distinct species are either sterile, or
their offspring, called hybrids, are so. It is affirmed not only that this
is an experimental fact, but that it is a provision for the preservation of
the purity of species. Such a criterion as this would be invaluable; but,
unfortunately, not only is it not obvious how to apply it in the great
majority of cases in which its aid is needed, but its general validity is
stoutly denied. The Hon. and Rev. Mr. Herbert, a most trustworthy
authority, not only asserts as the result of his own observations and
experiments that many hybrids are quite as fertile as the parent species,
but he goes so far as to assert that the particular plant _Crinum
capense_ is much more fertile when crossed by a distinct species than
when fertilised by its proper pollen! On the other hand, the famous
Gaertner, though he took the greatest pains to cross the Primrose and the
Cowslip, succeeded only once or twice in several years; and yet it is a
well-established fact that the Primrose and the Cowslip are only varieties
of the same kind of plant. Again, such cases as the following are well
established. The female of species A, if crossed with the male of species
B, is fertile; but, if the female of B is crossed with the male of A, she
remains barren. Facts of this kind destroy the value of the supposed
criterion.
If, weary of the endless difficulties involved in the determination of
species, the investigator, contenting himself with the rough practical
distinction of separable kinds, endeavours to study them as they occur in
nature--to ascertain their relations to the conditions which surround them,
their mutual harmonies and discordancies of structure, the bond of union of
their present and their past history, he finds himself, according to the
received notions, in a mighty maze, and with, at most, the dimmest
adumbration of a plan. If he starts with any one clear conviction, it is
that every part of a living creature is cunningly adapted to some special
use in its life. Has not his Paley told him that that seemingly useless
organ, the spleen, is beautifully adjusted as so much packing between the
other organs? And yet, at the outset of his studies, he finds that no
adaptive reason whatsoever can be given for one-half of the peculiarities
of vegetable structure. He also discovers rudimentary teeth, which are
never used, in the gums of the young calf and in those of the foetal whale;
insects which never bite have rudimental jaws, and others which never fly
have rudimental wings; naturally blind creatures have rudimental eyes; and
the halt have rudimentary limbs. So, again, no animal or plant puts on its
perfect form at once, but all have to start from the same point, however
various the course which each has to pursue. Not only men and horses, and
cats and dogs, lobsters and beetles, periwinkles and mussels, but even the
very sponges and animalcules commence their existence under forms which are
essentially undistinguishable; and this is true of all the infinite variety
of plants. Nay, more, all living beings march, side by side, along the high
road of development, and separate the later the more like they are; like
people leaving church, who all go down the aisle, but having reached the
door, some turn into the parsonage, others go down the village, and others
part only in the next parish. A man in his development runs for a little
while parallel with, though never passing through, the form of the meanest
worm, then travels for a space beside the fish, then journeys along with
the bird and the reptile for his fellow travellers: and only at last, after
a brief companionship with the highest of the four-footed and four-handed
world, rises into the dignity of pure manhood. No competent thinker of the
present day dreams of explaining these indubitable facts by the notion of
the existence of unknown and undiscoverable adaptations to purpose. And we
would remind those who, ignorant of the facts, must be moved by authority,
that no one has asserted the incompetence of the doctrine of final causes,
in its application to physiology and anatomy, more strongly than our own
eminent anatomist, Professor Owen, who, speaking of such cases, says ("On
the Nature of Limbs," pp. 39, 40)--"I think it will be obvious that the
principle of final adaptations fails to satisfy all the conditions of the
problem."
But, if the doctrine of final causes will not help us to comprehend
the anomalies of living structure, the principle of adaptation must
surely lead us to understand why certain living beings are found in
certain regions of the world and not in others. The Palm, as we know,
will not grow in our climate, nor the Oak in Greenland. The white bear
cannot live where the tiger thrives, nor _vice versâ_, and the more
the natural habits of animal and vegetable species are examined, the
more do they seem, on the whole, limited to particular provinces. But
when we look into the facts established by the study of the
geographical distribution of animals and plants it seems utterly
hopeless to attempt to understand the strange and apparently
capricious relations which they exhibit. One would be inclined to
suppose _à priori_ that every country must be naturally peopled by
those animals that are fittest to live and thrive in it. And yet how,
on this hypothesis, are we to account for the absence of cattle in the
Pampas of South America, when those parts of the New World were
discovered? It is not that they were unfit for cattle, for millions of
cattle now run wild there; and the like holds good of Australia and
New Zealand. It is a curious circumstance, in fact, that the animals
and plants of the Northern Hemisphere are not only as well adapted to
live in the Southern Hemisphere as its own autochthones, but are, in
many cases, absolutely better adapted, and so overrun and extirpate
the aborigines. Clearly, therefore, the species which naturally
inhabit a country are not necessarily the best adapted to its climate
and other conditions. The inhabitants of islands are often distinct
from any other known species of animal or plants (witness our recent
examples from the work of Sir Emerson Tennent, on Ceylon), and yet
they have almost always a sort of general family resemblance to the
animals and plants of the nearest mainland. On the other hand, there
is hardly a species of fish, shell, or crab common to the opposite
sides of the narrow isthmus of Panama. [Footnote: See page 60
_Note_.] Wherever we look, then, living nature offers us riddles of
difficult solution, if we suppose that what we see is all that can be
known of it.
But our knowledge of life is not confined to the existing world. Whatever
their minor differences, geologists are agreed as to the vast thickness of
the accumulated strata which compose the visible part of our earth, and the
inconceivable immensity of the time the lapse of which they are the
imperfect but the only accessible witnesses. Now, throughout the greater
part of this long series of stratified rocks are scattered, sometimes very
abundantly, multitudes of organic remains, the fossilised exuviæ of animals
and plants which lived and died while the mud of which the rocks are formed
was yet soft ooze, and could receive and bury them. It would be a great
error to suppose that these organic remains were fragmentary relics. Our
museums exhibit fossil shells of immeasurable antiquity, as perfect as the
day they were formed; whole skeletons without a limb disturbed; nay, the
changed flesh, the developing embryos, and even the very footsteps of
primæval organisms. Thus the naturalist finds in the bowels of the earth
species as well defined as, and in some groups of animals more numerous
than, those which breathe the upper air. But, singularly enough, the
majority of these entombed species are wholly distinct from those that now
live. Nor is this unlikeness without its rule and order. As a broad fact,
the further we go back in time the less the buried species are like
existing forms; and, the further apart the sets of extinct creatures are,
the less they are like one another. In other words, there has been a
regular succession of living beings, each younger set, being in a very
broad and general sense, somewhat more like those which now live.
It was once supposed that this succession had been the result of vast
successive catastrophes, destructions, and re-creations _en masse_;
but catastrophes are now almost eliminated from geological, or at least
palæontological speculation; and it is admitted, on all hands, that the
seeming breaks in the chain of being are not absolute, but only relative to
our imperfect knowledge; that species have replaced species, not in
assemblages, but one by one; and that, if it were possible to have all the
phenomena of the past presented to us, the convenient epochs and formations
of the geologist, though having a certain distinctness, would fade into one
another with limits as undefinable as those of the distinct and yet
separable colours of the solar spectrum.
Such is a brief summary of the main truths which have been established
concerning species. Are these truths ultimate and irresolvable facts, or
are their complexities and perplexities the mere expressions of a higher
law?
A large number of persons practically assume the former position to be
correct. They believe that the writer of the Pentateuch was empowered and
commissioned to teach us scientific as well as other truth, that the
account we find there of the creation of living things is simply and
literally correct, and that anything which seems to contradict it is, by
the nature of the case, false. All the phenomena which have been detailed
are, on this view, the immediate product of a creative fiat and,
consequently, are out of the domain of science altogether.
Whether this view prove ultimately to be true or false, it is, at any rate,
not at present supported by what is commonly regarded as logical proof,
even if it be capable of discussion by reason; and hence we consider
ourselves at liberty to pass it by, and to turn to those views which
profess to rest on a scientific basis only, and therefore admit of being
argued to their consequences. And we do this with the less hesitation as it
so happens that those persons who are practically conversant with the facts
of the case (plainly a considerable advantage) have always thought fit to
range themselves under the latter category.
The majority of these competent persons have up to the present time
maintained two positions--the first, that every species is, within certain
defined limits, fixed and incapable of modification; the second, that every
species was originally produced by a distinct creative act. The second
position is obviously incapable of proof or disproof, the direct operations
of the Creator not being subjects of science; and it must therefore be
regarded as a corollary from the first, the truth or falsehood of which is
a matter of evidence. Most persons imagine that the arguments in favour of
it are overwhelming; but to some few minds, and these, it must be
confessed, intellects of no small power and grasp of knowledge, they have
not brought conviction. Among these minds, that of the famous naturalist
Lamarck, who possessed a greater acquaintance with the lower forms of life
than any man of his day, Cuvier not excepted, and was a good botanist to
boot, occupies a prominent place.
Two facts appear to have strongly affected the course of thought of this
remarkable man--the one, that finer or stronger links of affinity connect
all living beings with one another, and that thus the highest creature
grades by multitudinous steps into the lowest; the other, that an organ may
be developed in particular directions by exerting itself in particular
ways, and that modifications once induced may be transmitted and become
hereditary. Putting these facts together, Lamarck endeavoured to account
for the first by the operation of the second. Place an animal in new
circumstances, says he, and its needs will be altered; the new needs will
create new desires, and the attempt to gratify such desires will result in
an appropriate modification of the organs exerted. Make a man a blacksmith,
and his brachial muscles will develop in accordance with the demands made
upon them, and in like manner, says Lamarck, "the efforts of some
short-necked bird to catch fish without wetting himself have, with time and
perseverance, given rise to all our herons and long-necked waders."
The Lamarckian hypothesis has long since been justly condemned, and it is
the established practice for every tyro to raise his heel against the
carcase of the dead lion. But it is rarely either wise or instructive to
treat even the errors of a really great man with mere ridicule, and in the
present case the logical form of the doctrine stands on a very different
footing from its substance.
If species have really arisen by the operation of natural conditions, we
ought to be able to find those conditions now at work; we ought to be able
to discover in nature some power adequate to modify any given kind of
animal or plant in such a manner as to give rise to another kind, which
would be admitted by naturalists as a distinct species. Lamarck imagined
that he had discovered this _vera causa_ in the admitted facts that
some organs may be modified by exercise; and that modifications, once
produced, are capable of hereditary transmission. It does not seem to have
occurred to him to inquire whether there is any reason to believe that
there are any limits to the amount of modification producible, or to ask
how long an animal is likely to endeavour to gratify an impossible desire.
The bird, in our example, would surely have renounced fish dinners long
before it had produced the least effect on leg or neck.
Since Lamarck's time, almost all competent naturalists have left
speculations on the origin of species to such dreamers as the author of the
"Vestiges," by whose well-intentioned efforts the Lamarckian theory
received its final condemnation in the minds of all sound thinkers.
Notwithstanding this silence, however, the transmutation theory, as it has
been called, has been a "skeleton in the closet" to many an honest
zoologist and botanist who had a soul above the mere naming of dried plants
and skins. Surely, has such an one thought, nature is a mighty and
consistent whole, and the providential order established in the world of
life must, if we could only see it rightly, be consistent with that
dominant over the multiform shapes of brute matter. But what is the history
of astronomy, of all the branches of physics, of chemistry, of medicine,
but a narration of the steps by which the human mind has been compelled,
often sorely against its will, to recognise the operation of secondary
causes in events where ignorance beheld an immediate intervention of a
higher power? And when we know that living things are formed of the same
elements as the inorganic world, that they act and react upon it, bound by
a thousand ties of natural piety, is it probable, nay is it possible, that
they, and they alone, should have no order in their seeming disorder, no
unity in their seeming multiplicity, should suffer no explanation by the
discovery of some central and sublime law of mutual connection?
Questions of this kind have assuredly often arisen, but it might have been
long before they received such expression as would have commanded the
respect and attention of the scientific world, had it not been for the
publication of the work which prompted this article. Its author, Mr.
Darwin, inheritor of a once celebrated name, won his spurs in science when
most of those now distinguished were young men, and has for the last twenty
years held a place in the front ranks of British philosophers. After a
circumnavigatory voyage, undertaken solely for the love of his science, Mr.
Darwin published a series of researches which at once arrested the
attention of naturalists and geologists; his generalisations have since
received ample confirmation and now command universal assent, nor is it
questionable that they have had the most important influence on the
progress of science. More recently Mr. Darwin, with a versatility which is
among the rarest of gifts, turned his attention to a most difficult
question of zoology and minute anatomy; and no living naturalist and
anatomist has published a better monograph than that which resulted from
his labours. Such a man, at all events, has not entered the sanctuary with
unwashed hands, and when he lays before us the results of twenty years'
investigation and reflection we must listen even though we be disposed to
strike. But, in reading his work, it must be confessed that the attention
which might at first be dutifully, soon becomes willingly, given, so clear
is the author's thought, so outspoken his conviction, so honest and fair
the candid expression of his doubts. Those who would judge the book must
read it: we shall endeavour only to make its line of argument and its
philosophical position intelligible to the general reader in our own way.
The Baker Street Bazaar has just been exhibiting its familiar annual
spectacle. Straight-backed, small-headed, big-barrelled oxen, as dissimilar
from any wild species as can well be imagined, contended for attention and
praise with sheep of half-a-dozen different breeds and styes of bloated
preposterous pigs, no more like a wild boar or sow than a city alderman is
like an ourang-outang. The cattle show has been, and perhaps may again be,
succeeded by a poultry show, of whose crowing and clucking prodigies it can
only be certainly predicated that they will be very unlike the aboriginal
_Phasianus gallus._ If the seeker after animal anomalies is not
satisfied, a turn or two in Seven Dials will convince him that the breeds
of pigeons are quite as extraordinary and unlike one another and their
parent stock, while the Horticultural Society will provide him with any
number of corresponding vegetable aberrations from nature's types. He will
learn with no little surprise, too, in the course of his travels, that the
proprietors and producers of these animal and vegetable anomalies regard
them as distinct species, with a firm belief, the strength of which is
exactly proportioned to their ignorance of scientific biology, and which is
the more remarkable as they are all proud of their skill in originating
such "species."
On careful inquiry it is found that all these, and the many other
artificial breeds or races of animals and plants, have been produced by one
method. The breeder--and a skilful one must be a person of much sagacity
and natural or acquired perceptive faculty--notes some slight difference,
arising he knows not how, in some individuals of his stock. If he wish to
perpetuate the difference, to form a breed with the peculiarity in question
strongly marked, he selects such male and female individuals as exhibit the
desired character, and breeds from them. Their offspring are then carefully
examined, and those which exhibit the peculiarity the most distinctly are
selected for breeding; and this operation is repeated until the desired
amount of divergence from the primitive stock is reached. It is then found
that by continuing the process of selection--always breeding, that is, from
well-marked forms, and allowing no impure crosses to interfere--a race may
be formed, the tendency of which to reproduce itself is exceedingly strong;
nor is the limit to the amount of divergence which may be thus produced
known; but one thing is certain, that, if certain breeds of dogs, or of
pigeons, or of horses, were known only in a fossil state, no naturalist
would hesitate in regarding them as distinct species.
But in all these cases we have human interference. Without the breeder
there would be no selection, and without the selection no race. Before
admitting the possibility of natural species having originated in any
similar way, it must be proved that there is in Nature some power which
takes the place of man, and performs a selection _suâ sponte._ It is
the claim of Mr. Darwin that he professes to have discovered the existence
and the _modus operandi_ of this "natural selection," as he terms it;
and, if he be right, the process is perfectly simple and comprehensible,
and irresistibly deducible from very familiar but well nigh forgotten
facts.
Who, for instance, has duly reflected upon all the consequences of the
marvellous struggle for existence which is daily and hourly going on among
living beings? Not only does every animal live at the expense of some other
animal or plant, but the very plants are at war. The ground is full of
seeds that cannot rise into seedlings; the seedlings rob one another of
air, light and water, the strongest robber winning the day, and
extinguishing his competitors. Year after year, the wild animals with which
man never interferes are, on the average, neither more nor less numerous
than they were; and yet we know that the annual produce of every pair is
from one to perhaps a million young; so that it is mathematically certain
that, on the average, as many are killed by natural causes as are born
every year, and those only escape which happen to be a little better fitted
to resist destruction than those which die. The individuals of a species
are like the crew of a foundered ship, and none but good swimmers have a
chance of reaching the land.
Such being unquestionably the necessary conditions under which living
creatures exist, Mr. Darwin discovers in them the instrument of natural
selection. Suppose that in the midst of this incessant competition some
individuals of a species (A) present accidental variations which happen to
fit them a little better than their fellows for the struggle in which they
are engaged, then the chances are in favour, not only of these individuals
being better nourished than the others, but of their predominating over
their fellows in other ways, and of having a better chance of leaving
offspring, which will of course tend to reproduce the peculiarities of
their parents. Their offspring will, by a parity of reasoning, tend to
predominate over their contemporaries, and there being (suppose) no room
for more than one species such as A, the weaker variety will eventually be
destroyed by the new destructive influence which is thrown into the scale,
and the stronger will take its place. Surrounding conditions remaining
unchanged, the new variety (which we may call B)--supposed, for argument's
sake, to be the best adapted for these conditions which can be got out of
the original stock--will remain unchanged, all accidental deviations from
the type becoming at once extinguished, as less fit for their post than B
itself. The tendency of B to persist will grow with its persistence through
successive generations, and it will acquire all the characters of a new
species.
But, on the other hand, if the conditions of life change in any degree,
however slight, B may no longer be that form which is best adapted to
withstand their destructive, and profit by their sustaining, influence; in
which case if it should give rise to a more competent variety (C), this
will take its place and become a new species; and thus, by natural
selection, the species B and C will be successively derived from A.
That this most ingenious hypothesis enables us to give a reason for many
apparent anomalies in the distribution of living beings in time and space,
and that it is not contradicted by the main phenomena of life and
organisation appear to us to be unquestionable; and, so far, it must be
admitted to have an immense advantage over any of its predecessors. But it
is quite another matter to affirm absolutely either the truth or falsehood
of Mr. Darwin's views at the present stage of the inquiry. Goethe has an
excellent aphorism defining that state of mind which he calls "Thätige
Skepsis"--active doubt. It is doubt which so loves truth that it neither
dares rest in doubting, nor extinguish itself by unjustified belief; and we
commend this state of mind to students of species, with respect to Mr.
Darwin's or any other hypothesis, as to their origin. The combined
investigations of another twenty years may, perhaps, enable naturalists to
say whether the modifying causes and the selective power, which Mr. Darwin
has satisfactorily shown to exist in Nature, are competent to produce all
the effects he ascribes to them; or whether, on the other hand, he has been
led to over-estimate the value of the principle of natural selection, as
greatly as Lamarck over-estimated his _vera causa_ of modification by
exercise.
But there is, at all events, one advantage possessed by the more recent
writer over his predecessor. Mr. Darwin abhors mere speculation as nature
abhors a vacuum. He is as greedy of cases and precedents as any
constitutional lawyer, and all the principles he lays down are capable of
being brought to the test of observation and experiment. The path he bids
us follow professes to be, not a mere airy track, fabricated of ideal
cobwebs, but a solid and broad bridge of facts. If it be so, it will carry
us safely over many a chasm in our knowledge, and lead us to a region free
from the snares of those fascinating but barren virgins, the Final Causes,
against whom a high authority has so justly warned us. "My sons, dig in the
vineyard," were the last words of the old man in the fable: and, though the
sons found no treasure, they made their fortunes by the grapes.
II
THE ORIGIN OF SPECIES
[1860]
Mr. Darwin's long-standing and well-earned scientific eminence probably
renders him indifferent to that social notoriety which passes by the name
of success; but if the calm spirit of the philosopher have not yet wholly
superseded the ambition and the vanity of the carnal man within him, he
must be well satisfied with the results of his venture in publishing the
"Origin of Species." Overflowing the narrow bounds of purely scientific
circles, the "species question" divides with Italy and the Volunteers the
attention of general society. Everybody has read Mr. Darwin's book, or, at
least, has given an opinion upon its merits or demerits; pietists, whether
lay or ecclesiastic, decry it with the mild railing which sounds so
charitable; bigots denounce it with ignorant invective; old ladies of both
sexes consider it a decidedly dangerous book, and even savants, who have no
better mud to throw, quote antiquated writers to show that its author is no
better than an ape himself; while every philosophical thinker hails it as a
veritable Whitworth gun in the armoury of liberalism; and all competent
naturalists and physiologists, whatever their opinions as to the ultimate
fate of the doctrines put forth, acknowledge that the work in which they
are embodied is a solid contribution to knowledge and inaugurates a new
epoch in natural history.
Nor has the discussion of the subject been restrained within the limits of
conversation. When the public is eager and interested, reviewers must
minister to its wants; and the genuine _littérateur_ is too much in
the habit of acquiring his knowledge from the book he judges--as the
Abyssinian is said to provide himself with steaks from the ox which carries
him--to be withheld from criticism of a profound scientific work by the
mere want of the requisite preliminary scientific acquirement; while, on
the other hand, the men of science who wish well to the new views, no less
than those who dispute their validity, have naturally sought opportunities
of expressing their opinions. Hence it is not surprising that almost all
the critical journals have noticed Mr. Darwin's work at greater or less
length; and so many disquisitions, of every degree of excellence, from the
poor product of ignorance, too often stimulated by prejudice, to the fair
and thoughtful essay of the candid student of Nature, have appeared, that
it seems an almost hopeless task to attempt to say anything new upon the
question.
But it may be doubted if the knowledge and acumen of prejudged scientific
opponents, and the subtlety of orthodox special pleaders, have yet exerted
their full force in mystifying the real issues of the great controversy
which has been set afoot, and whose end is hardly likely to be seen by this
generation; so that, at this eleventh hour, and even failing anything new,
it may be useful to state afresh that which is true, and to put the
fundamental positions advocated by Mr. Darwin in such a form that they may
be grasped by those whose special studies lie in other directions. And the
adoption of this course may be the more advisable, because, notwithstanding
its great deserts, and indeed partly on account of them, the "Origin of
Species" is by no means an easy book to read--if by reading is implied the
full comprehension of an author's meaning.
We do not speak jestingly in saying that it is Mr. Darwin's misfortune to
know more about the question he has taken up than any man living.
Personally and practically exercised in zoology, in minute anatomy, in
geology; a student of geographical distribution, not on maps and in museums
only, but by long voyages and laborious collection; having largely advanced
each of these branches of science, and having spent many years in gathering
and sifting materials for his present work, the store of accurately
registered facts upon which the author of the "Origin of Species" is able
to draw at will is prodigious.
But this very superabundance of matter must have been embarrassing to a
writer who, for the present, can only put forward an abstract of his views;
and thence it arises, perhaps, that notwithstanding the clearness of the
style, those who attempt fairly to digest the book find much of it a sort
of intellectual pemmican--a mass of facts crushed and pounded into shape,
rather than held together by the ordinary medium of an obvious logical
bond; due attention will, without doubt, discover this bond, but it is
often hard to find.
Again, from sheer want of room, much has to be taken for granted which
might readily enough be proved; and hence, while the adept, who can supply
the missing links in the evidence from his own knowledge, discovers fresh
proof of the singular thoroughness with which all difficulties have been
considered and all unjustifiable suppositions avoided, at every reperusal
of Mr. Darwin's pregnant paragraphs, the novice in biology is apt to
complain of the frequency of what he fancies is gratuitous assumption.
Thus while it may be doubted if, for some years, any one is likely to be
competent to pronounce judgment on all the issues raised by Mr. Darwin,
there is assuredly abundant room for him, who, assuming the humbler, though
perhaps as useful, office of an interpreter between the "Origin of Species"
and the public, contents himself with endeavouring to point out the nature
of the problems which it discusses; to distinguish between the ascertained
facts and the theoretical views which it contains; and finally, to show the
extent to which the explanation it offers satisfies the requirements of
scientific logic. At any rate, it is this office which we purpose to
undertake in the following pages.
It may be safely assumed that our readers have a general conception of the
nature of the objects to which the word "species" is applied; but it has,
perhaps, occurred to a few, even to those who are naturalists _ex
professo_, to reflect, that, as commonly employed, the term has a double
sense and denotes two very different orders of relations. When we call a
group of animals, or of plants, a species, we may imply thereby, either
that all these animals or plants have some common peculiarity of form or
structure; or, we may mean that they possess some common functional
character. That part of biological science which deals with form and
structure is called Morphology--that which concerns itself with function,
Physiology--so that we may conveniently speak of these two senses, or
aspects, of "species"--the one as morphological, the other as
physiological. Regarded from the former point of view, a species is nothing
more than a kind of animal or plant, which is distinctly definable from all
others, by certain constant, and not merely sexual, morphological
peculiarities. Thus horses form a species, because the group of animals to
which that name is applied is distinguished from all others in the world by
the following constantly associated characters. They have--1, A vertebral
column; 2, Mammae; 3, A placental embryo; 4, Four legs; 5, A single
well-developed toe in each foot provided with a hoof; 6, A bushy tail; and
7, Callosities on the inner sides of both the fore and the hind legs. The
asses, again, form a distinct species, because, with the same characters,
as far as the fifth in the above list, all asses have tufted tails, and
have callosities only on the inner side of the fore-legs. If animals were
discovered having the general characters of the horse, but sometimes with
callosities only on the fore-legs, and more or less tufted tails; or
animals having the general characters of the ass, but with more or less
bushy tails, and sometimes with callosities on both pairs of legs, besides
being intermediate in other respects--the two species would have to be
merged into one. They could no longer be regarded as morphologically
distinct species, for they would not be distinctly definable one from the
other.
However bare and simple this definition of species may appear to be, we
confidently appeal to all practical naturalists, whether zoologists,
botanists, or palaeontologists, to say if, in the vast majority of cases,
they know, or mean to affirm, anything more of the group of animals or
plants they so denominate than what has just been stated. Even the most
decided advocates of the received doctrines respecting species admit this.
"I apprehend," says Professor Owen, [Footnote: "On the Osteology of the
Chimpanzees and Orangs"; _Transactions of the Zoological Society_,
1858.] "that few naturalists nowadays, in describing and proposing a name
for what they call 'a new _species_,' use that term to signify what
was meant by it twenty or thirty years ago; that is, an originally distinct
creation, maintaining its primitive distinction by obstructive generative
peculiarities. The proposer of the new species now intends to state no more
than he actually knows; as, for example, that the differences on which he
founds the specific character are constant in individuals of both sexes, so
far as observation has reached; and that they are not due to domestication
or to artificially superinduced external circumstances, or to any outward
influence within his cognizance; that the species is wild, or is such as it
appears by Nature."
If we consider, in fact, that by far the largest proportion of recorded
existing species are known only by the study of their skins, or bones, or
other lifeless exuviae; that we are acquainted with none, or next to none,
of their physiological peculiarities, beyond those which can be deduced
from their structure, or are open to cursory observation; and that we
cannot hope to learn more of any of those extinct forms of life which now
constitute no inconsiderable proportion of the known Flora and Fauna of the
world: it is obvious that the definitions of these species can be only of a
purely structural, or morphological, character. It is probable that
naturalists would have avoided much confusion of ideas if they had more
frequently borne the necessary limitations of our knowledge in mind. But
while it may safely be admitted that we are acquainted with only the
morphological characters of the vast majority of species--the functional or
physiological, peculiarities of a few have been carefully investigated, and
the result of that study forms a large and most interesting portion of the
physiology of reproduction.
The student of Nature wonders the more and is astonished the less, the more
conversant he becomes with her operations; but of all the perennial
miracles she offers to his inspection, perhaps the most worthy of
admiration is the development of a plant or of an animal from its embryo.
Examine the recently laid egg of some common animal, such as a salamander
or newt. It is a minute spheroid in which the best microscope will reveal
nothing but a structureless sac, enclosing a glairy fluid, holding granules
in suspension. [Footnote: When this sentence was written, it was generally
believed that the original nucleus of the egg (the germinal vesicle)
disappeared. 1893.] But strange possibilities lie dormant in that
semi-fluid globule. Let a moderate supply of warmth reach its watery
cradle, and the plastic matter undergoes changes so rapid, yet so steady
and purposelike in their succession, that one can only compare them to
those operated by a skilled modeller upon a formless lump of clay. As with
an invisible trowel, the mass is divided and subdivided into smaller and
smaller portions, until it is reduced to an aggregation of granules not too
large to build withal the finest fabrics of the nascent organism. And,
then, it is as if a delicate finger traced out the line to be occupied by
the spinal column, and moulded the contour of the body; pinching up the
head at one end, the tail at the other, and fashioning flank and limb into
due salamandrine proportions, in so artistic a way, that, after watching
the process hour by hour, one is almost involuntarily possessed by the
notion, that some more subtle aid to vision than an achromatic, would show
the hidden artist, with his plan before him, striving with skilful
manipulation to perfect his work.
As life advances, and the young amphibian ranges the waters, the terror of
his insect contemporaries, not only are the nutritious particles supplied
by its prey, by the addition of which to its frame, growth takes place,
laid down, each in its proper spot, and in such due proportion to the rest,
as to reproduce the form, the colour, and the size, characteristic of the
parental stock; but even the wonderful powers of reproducing lost parts
possessed by these animals are controlled by the same governing tendency.
Cut off the legs, the tail, the jaws, separately or all together, and, as
Spallanzani showed long ago, these parts not only grow again, but the
redintegrated limb is formed on the same type as those which were lost. The
new jaw, or leg, is a newt's, and never by any accident more like that of a
frog. What is true of the newt is true of every animal and of every plant;
the acorn tends to build itself up again into a woodland giant such as that
from whose twig it fell; the spore of the humblest lichen reproduces the
green or brown incrustation which gave it birth; and at the other end of
the scale of life, the child that resembled neither the paternal nor the
maternal side of the house would be regarded as a kind of monster.
So that the one end to which, in all living beings, the formative impulse
is tending--the one scheme which the Archæus of the old speculators strives
to carry out, seems to be to mould the offspring into the likeness of the
parent. It is the first great law of reproduction, that the offspring tends
to resemble its parent or parents, more closely than anything else.
Science will some day show us how this law is a necessary consequence of
the more general laws which govern matter; but, for the present, more can
hardly be said than that it appears to be in harmony with them. We know
that the phænomena of vitality are not something apart from other physical
phænomena, but one with them; and matter and force are the two names of the
one artist who fashions the living as well as the lifeless. Hence living
bodies should obey the same great laws as other matter--nor, throughout
Nature, is there a law of wider application than this, that a body impelled
by two forces takes the direction of their resultant. But living bodies may
be regarded as nothing but extremely complex bundles of forces held in a
mass of matter, as the complex forces of a magnet are held in the steel by
its coercive force; and, since the differences of sex are comparatively
slight, or, in other words, the sum of the forces in each has a very
similar tendency, their resultant, the offspring, may reasonably be
expected to deviate but little from a course parallel to either, or to
both.
Represent the reason of the law to ourselves by what physical metaphor or
analogy we will, however, the great matter is to apprehend its existence
and the importance of the consequences deducible from it. For things which
are like to the same are like to one another; and if, in a great series of
generations, every offspring is like its parent, it follows that all the
offspring and all the parents must be like one another; and that, given an
original parental stock, with the opportunity of undisturbed
multiplication, the law in question necessitates the production, in course
of time, of an indefinitely large group, the whole of the members of which
are at once very similar and are blood relations, having descended from the
same parent, or pair of parents. The proof that all the members of any
given group of animals, or plants, had thus descended, would be ordinarily
considered sufficient to entitle them to the rank of physiological species,
for most physiologists consider species to be definable as "the offspring
of a single primitive stock."
But though it is quite true that all those groups we call species
_may_, according to the known laws of reproduction, have descended
from a single stock, and though it is very likely they really have done so,
yet this conclusion rests on deduction and can hardly hope to establish
itself upon a basis of observation. And the primitiveness of the supposed
single stock, which, after all, is the essential part of the matter, is not
only a hypothesis, but one which has not a shadow of foundation, if by
"primitive" be meant "independent of any other living being." A scientific
definition, of which an unwarrantable hypothesis forms an essential part,
carries its condemnation within itself; but, even supposing such a
definition were, in form, tenable, the physiologist who should attempt to
apply it in Nature would soon find himself involved in great, if not
inextricable, difficulties. As we have said, it is indubitable that
offspring _tend_ to resemble the parental organism, but it is equally
true that the similarity attained never amounts to identity either in form
or in structure. There is always a certain amount of deviation, not only
from the precise characters of a single parent, but when, as in most
animals and many plants, the sexes are lodged in distinct individuals, from
an exact mean between the two parents. And indeed, on general principles,
this slight deviation seems as intelligible as the general similarity, if
we reflect how complex the co-operating "bundles of forces" are, and how
improbable it is that, in any case, their true resultant shall coincide
with any mean between the more obvious characters of the two parents.
Whatever be its cause, however, the co-existence of this tendency to minor
variation with the tendency to general similarity, is of vast importance in
its bearing on the question of the origin of species.
As a general rule, the extent to which an offspring differs from its parent
is slight enough; but, occasionally, the amount of difference is much more
strongly marked, and then the divergent offspring receives the name of a
Variety. Multitudes, of what there is every reason to believe are such
varieties, are known, but the origin of very few has been accurately
recorded, and of these we will select two as more especially illustrative
of the main features of variation. The first of them is that of the "Ancon"
or "Otter" sheep, of which a careful account is given by Colonel David
Humphreys, F.R.S., in a letter to Sir Joseph Banks, published in the
"Philosophical Transactions" for 1813. It appears that one Seth Wright, the
proprietor of a farm on the banks of the Charles River, in Massachusetts,
possessed a flock of fifteen ewes and a ram of the ordinary kind. In the
year 1791, one of the ewes presented her owner with a male lamb, differing,
for no assignable reason, from its parents by a proportionally long body
and short bandy legs, whence it was unable to emulate its relatives in
those sportive leaps over the neighbours' fences, in which they were in the
habit of indulging, much to the good farmer's vexation.
The second case is that detailed by a no less unexceptionable authority
than Réaumur, in his "Art de faire éclore les Poulets." A Maltese couple,
named Kelleia, whose hands and feet were constructed upon the ordinary
human model, had born to them a son, Gratio, who possessed six perfectly
movable fingers on each hand, and six toes, not quite so well formed, on
each foot. No cause could be assigned for the appearance of this unusual
variety of the human species.
Two circumstances are well worthy of remark in both these cases. In each,
the variety appears to have arisen in full force, and, as it were, _per
saltum_; a wide and definite difference appearing, at once, between the
Ancon ram and the ordinary sheep; between the six-fingered and six-toed
Gratio Kelleia and ordinary men. In neither case is it possible to point
out any obvious reason for the appearance of the variety. Doubtless there
were determining causes for these as for all other phenomena; but they do
not appear, and we can be tolerably certain that what are ordinarily
understood as changes in physical conditions, as in climate, in food, or
the like, did not take place and had nothing to do with the matter. It was
no case of what is commonly called adaptation to circumstances; but, to use
a conveniently erroneous phrase, the variations arose spontaneously. The
fruitless search after final causes leads their pursuers a long way; but
even those hardy teleologists, who are ready to break through all the laws
of physics in chase of their favourite will-o'-the-wisp, may be puzzled to
discover what purpose could be attained by the stunted legs of Seth
Wright's ram or the hexadactyle members of Gratio Kelleia.
Varieties then arise we know not why; and it is more than probable that the
majority of varieties have arisen in this "spontaneous" manner, though we
are, of course, far from denying that they may be traced, in some cases, to
distinct external influences; which are assuredly competent to alter the
character of the tegumentary covering, to change colour, to increase or
diminish the size of muscles, to modify constitution, and, among plants, to
give rise to the metamorphosis of stamens into petals, and so forth. But
however they may have arisen, what especially interests us at present is,
to remark that, once in existence, many varieties obey the fundamental law
of reproduction that like tends to produce like; and their offspring
exemplify it by tending to exhibit the same deviation from the parental
stock as themselves. Indeed, there seems to be, in many instances, a
prepotent influence about a newly-arisen variety which gives it what one
may call an unfair advantage over the normal descendants from the same
stock. This is strikingly exemplified by the case of Gratio Kelleia, who
married a woman with the ordinary pentadactyle extremities, and had by her
four children, Salvator, George, André, and Marie. Of these children
Salvator, the eldest boy, had six fingers and six toes, like his father;
the second and third, also boys, had five fingers and five toes, like their
mother, though the hands and feet of George were slightly deformed. The
last, a girl, had five fingers and five toes, but the thumbs were slightly
deformed. The variety thus reproduced itself purely in the eldest, while
the normal type reproduced itself purely in the third, and almost purely in
the second and last: so that it would seem, at first, as if the normal type
were more powerful than the variety. But all these children grew up and
intermarried with normal wives and husband, and then, note what took place:
Salvator had four children, three of whom exhibited the hexadactyle members
of their grandfather and father, while the youngest had the pentadactyle
limbs of the mother and grandmother; so that here, notwithstanding a double
pentadactyle dilution of the blood, the hexadactyle variety had the best of
it. The same pre-potency of the variety was still more markedly exemplified
in the progeny of two of the other children, Marie and George. Marie (whose
thumbs only were deformed) gave birth to a boy with six toes, and three
other normally formed children; but George, who was not quite so pure a
pentadactyle, begot, first, two girls, each of whom had six fingers and
toes; then a girl with six fingers on each hand and six toes on the right
foot, but only five toes on the left; and lastly, a boy with only five
fingers and toes. In these instances, therefore, the variety, as it were,
leaped over one generation to reproduce itself in full force in the next.
Finally, the purely pentadactyle André was the father of many children, not
one of whom departed from the normal parental type.
If a variation which approaches the nature of a monstrosity can strive thus
forcibly to reproduce itself, it is not wonderful that less aberrant
modifications should tend to be preserved even more strongly; and the
history of the Ancon sheep is, in this respect, particularly instructive.
With the "'cuteness" characteristic of their nation, the neighbours of the
Massachusetts farmer imagined it would be an excellent thing if all his
sheep were imbued with the stay-at-home tendencies enforced by Nature upon
the newly-arrived ram; and they advised Wright to kill the old patriarch of
his fold, and install the Ancon ram in his place. The result justified
their sagacious anticipations, and coincided very nearly with what occurred
to the progeny of Gratio Kelleia. The young lambs were almost always either
pure Ancons, or pure ordinary sheep.[Footnote: Colonel Humphreys'
statements are exceedingly explicit on this point:--. "When an Ancon ewe is
impregnated by a common ram, the increase resembles wholly either the ewe
or the ram. The increase of the common ewe impregnated by an Ancon ram
follows entirely the one or the other, without blending any of the
distinguishing and essential peculiarities of both. Frequent instances have
happened where common ewes have had twins by Ancon rams, when one exhibited
the complete marks and features of the ewe, the other of the ram. The
contrast has been rendered singularly striking, when one short-legged and
one long-legged lamb, produced at a birth, have been seen sucking the dam
at the same time."--_Philosophical Transactions_, 1813, Ft. I. pp. 89,
90.] But when sufficient Ancon sheep were obtained to interbreed with one
another, it was found that the offspring was always pure Ancon. Colonel
Humphreys, in fact, states that he was acquainted with only "one
questionable case of a contrary nature." Here, then, is a remarkable and
well-established instance, not only of a very distinct race being
established _per saltum_, but of that race breeding "true" at once,
and showing no mixed forms, even when crossed with another breed.
By taking care to select Ancons of both sexes, for breeding from, it thus
became easy to establish an extremely well-marked race; so peculiar that,
even when herded with other sheep, it was noted that the Ancons kept
together. And there is every reason to believe that the existence of this
breed might have been indefinitely protracted; but the introduction of the
Merino sheep, which were not only very superior to the Ancons in wool and
meat, but quite as quiet and orderly, led to the complete neglect of the
new breed, so that, in 1813, Colonel Humphreys found it difficult to obtain
the specimen, the skeleton of which was presented to Sir Joseph Banks. We
believe that, for many years, no remnant of it has existed in the United
States.
Gratio Kelleia was not the progenitor of a race of six-fingered men, as
Seth Wright's ram became a nation of Ancon sheep, though the tendency of
the variety to perpetuate itself appears to have been fully as strong in
the one case as in the other. And the reason of the difference is not far
to seek. Seth Wright took care not to weaken the Ancon blood by matching
his Ancon ewes with any but males of the same variety, while Gratio
Kelleia's sons were too far removed from the patriarchal times to
intermarry with their sisters; and his grand-children seem not to have been
attracted by their six-fingered cousins. In other words, in the one example
a race was produced, because, for several generations, care was taken to
_select_ both parents of the breeding stock from animals exhibiting a
tendency to vary in the same direction; while, in the other, no race was
evolved, because no such selection was exercised. A race is a propagated
variety; and as, by the laws of reproduction, offspring tend to assume the
parental forms, they will be more likely to propagate a variation exhibited
by both parents than that possessed by only one.
There is no organ of the body of an animal which may not, and does not,
occasionally, vary more or less from the normal type; and there is no
variation which may not be transmitted and which, if selectively
transmitted, may not become the foundation of a race. This great truth,
sometimes forgotten by philosophers, has long been familiar to practical
agriculturists and breeders; and upon it rest all the methods of improving
the breeds of domestic animals, which, for the last century, have been
followed with so much success in England. Colour, form, size, texture of
hair or wool, proportions of various parts, strength or weakness of
constitution, tendency to fatten or to remain lean, to give much or little
milk, speed, strength, temper, intelligence, special instincts; there is
not one of these characters the transmission of which is not an every-day
occurrence within the experience of cattle-breeders, stock-farmers,
horse-dealers, and dog and poultry fanciers. Nay, it is only the other day
that an eminent physiologist, Dr. Brown-Séquard, communicated to the Royal
Society his discovery that epilepsy, artificially produced in guinea-pigs,
by a means which he has discovered, is transmitted to their offspring.
[Footnote: Compare Weismann's _Essays Upon Heredity_, p. 310, _et
seq_. 1893.]
But a race, once produced, is no more a fixed and immutable entity than the
stock whence it sprang; variations arise among its members, and as these
variations are transmitted like any others, new races may be developed out
of the pre-existing one _ad infinitum_, or, at least, within any limit
at present determined. Given sufficient time and sufficiently careful
selection, and the multitude of races which may arise from a common stock
is as astonishing as are the extreme structural differences which they may
present. A remarkable example of this is to be found in the rock-pigeon,
which Mr. Darwin has, in our opinion, satisfactorily demonstrated to be the
progenitor of all our domestic pigeons, of which there are certainly more
than a hundred well-marked races. The most noteworthy of these races are,
the four great stocks known to the "fancy" as tumblers, pouters, carriers,
and fantails; birds which not only differ most singularly in size, colour,
and habits, but in the form of the beak and of the skull; in the
proportions of the beak to the skull; in the number of tail-feathers; in
the absolute and relative size of the feet; in the presence or absence of
the uropygial gland; in the number of vertebræ in the back; in short, in
precisely those characters in which the genera and species of birds differ
from one another.
And it is most remarkable and instructive to observe, that none of these
races can be shown to have been originated by the action of changes in what
are commonly called external circumstances, upon the wild rock-pigeon. On
the contrary, from time immemorial pigeon-fanciers have had essentially
similar methods of treating their pets, which have been housed, fed,
protected and cared for in much the same way in all pigeonries. In fact,
there is no case better adapted than that of the pigeons to refute the
doctrine which one sees put forth on high authority, that "no other
characters than those founded on the development of bone for the attachment
of muscles" are capable of variation. In precise contradiction of this
hasty assertion, Mr. Darwin's researches prove that the skeleton of the
wings in domestic pigeons has hardly varied at all from that of the wild
type; while, on the other hand, it is in exactly those respects, such as
the relative length of the beak and skull, the number of the vertebrae, and
the number of the tail-feathers, in which muscular exertion can have no
important influence, that the utmost amount of variation has taken place.
We have said that the following out of the properties exhibited by
physiological species would lead us into difficulties, and at this point
they begin to be obvious; for if, as the result of spontaneous variation
and of selective breeding, the progeny of a common stock may become
separated into groups distinguished from one another by constant, not
sexual, morphological characters, it is clear that the physiological
definition of species is likely to clash with the morphological definition.
No one would hesitate to describe the pouter and the tumbler as distinct
species, if they were found fossil, or if their skins and skeletons were
imported, as those of exotic wild birds commonly are--and without doubt, if
considered alone, they are good and distinct morphological species. On the
other hand, they are not physiological species, for they are descended from
a common stock, the rock-pigeon.
Under these circumstances, as it is admitted on all sides that races occur
in Nature, how are we to know whether any apparently distinct animals are
really of different physiological species, or not, seeing that the amount
of morphological difference is no safe guide? Is there any test of a
physiological species? The usual answer of physiologists is in the
affirmative. It is said that such a test is to be found in the phænomena of
hybridisation--in the results of crossing races, as compared with the
results of crossing species.
So far as the evidence goes at present, individuals, of what are certainly
known to be mere races produced by selection, however distinct they may
appear to be, not only breed freely together, but the offspring of such
crossed races are perfectly fertile with one another. Thus, the spaniel and
the greyhound, the dray-horse and the Arab, the pouter and the tumbler,
breed together with perfect freedom, and their mongrels, if matched with
other mongrels of the same kind, are equally fertile.
On the other hand, there can be no doubt that the individuals of many
natural species are either absolutely infertile if crossed with individuals
of other species, or, if they give rise to hybrid offspring, the hybrids so
produced are infertile when paired together. The horse and the ass, for
instance, if so crossed, give rise to the mule, and there is no certain
evidence of offspring ever having been produced by a male and female mule.
The unions of the rock-pigeon and the ring-pigeon appear to be equally
barren of result. Here, then, says the physiologist, we have a means of
distinguishing any two true species from any two varieties. If a male and a
female, selected from each group, produce offspring, and that offspring is
fertile with others produced in the same way, the groups are races and not
species. If, on the other hand, no result ensues, or if the offspring are
infertile with others produced in the same way, they are true physiological
species. The test would be an admirable one, if, in the first place, it
were always practicable to apply it, and if, in the second, it always
yielded results susceptible of a definite interpretation. Unfortunately, in
the great majority of cases, this touchstone for species is wholly
inapplicable.
The constitution of many wild animals is so altered by confinement that
they will not breed even with their own females, so that the negative
results obtained from crosses are of no value; and the antipathy of wild
animals of different species for one another, or even of wild and tame
members of the same species, is ordinarily so great, that it is hopeless to
look for such unions in Nature. The hermaphrodism of most plants, the
difficulty in the way of insuring the absence of their own or the proper
working of other pollen, are obstacles of no less magnitude in applying the
test to them. And, in both animals and plants, is super-added the further
difficulty, that experiments must be continued over a long time for the
purpose of ascertaining the fertility of the mongrel or hybrid progeny, as
well as of the first crosses from which they spring.
Not only do these great practical difficulties lie in the way of applying
the hybridisation test, but even when this oracle can be questioned, its
replies are sometimes as doubtful as those of Delphi. For example, cases
are cited by Mr. Darwin, of plants which are more fertile with the pollen
of another species than with their own; and there are others, such as
certain _Fuci,_ the male element of which will fertilise the ovule of
a plant of distinct species, while the males of the latter species are
ineffective with the females of the first. So that, in the last-named
instance, a physiologist, who should cross the two species in one way,
would decide that they were true species; while another, who should cross
them in the reverse way, would, with equal justice, according to the rule,
pronounce them to be mere races. Several plants, which there is great
reason to believe are mere varieties, are almost sterile when crossed;
while both animals and plants, which have always been regarded by
naturalists as of distinct species, turn out, when the test is applied, to
be perfectly fertile. Again, the sterility or fertility of crosses seems to
bear no relation to the structural resemblances or differences of the
members of any two groups.
Mr. Darwin has discussed this question with singular ability and
circumspection, and his conclusions are summed up as follows, at page 276
of his work:--
"First crosses between forms sufficiently distinct to be ranked as species,
and their hybrids, are very generally, but not universally, sterile. The
sterility is of all degrees, and is often so slight that the two most
careful experimentalists who have ever lived have come to diametrically
opposite conclusions in ranking forms by this test. The sterility is
innately variable in individuals of the same species, and is eminently
susceptible of favourable and unfavourable conditions. The degree of
sterility does not strictly follow systematic affinity, but is governed by
several curious and complex laws. It is generally different and sometimes
widely different, in reciprocal crosses between the same two species. It is
not always equal in degree in a first cross, and in the hybrid produced
from this cross.
"In the same manner as in grafting trees, the capacity of one species or
variety to take on another is incidental on generally unknown differences
in their vegetative systems; so in crossing, the greater or less facility
of one species to unite with another is incidental on unknown differences
in their reproductive systems. There is no more reason to think that
species have been specially endowed with various degrees of sterility to
prevent them crossing and breeding in Nature, than to think that trees have
been specially endowed with various and somewhat analogous degrees of
difficulty in being grafted together, in order to prevent them becoming
inarched in our forests.
"The sterility of first crosses between pure species, which have their
reproductive systems perfect, seems to depend on several circumstances; in
some cases largely on the early death of the embryo. The sterility of
hybrids which have their reproductive systems imperfect, and which have had
this system and their whole organisation disturbed by being compounded of
two distinct species, seems closely allied to that sterility which so
frequently affects pure species when their natural conditions of life have
been disturbed. This view is supported by a parallelism of another kind:
namely, that the crossing of forms, only slightly different, is favourable
to the vigour and fertility of the offspring; and that slight changes in
the conditions of life are apparently favourable to the vigour and
fertility of all organic beings. It is not surprising that the degree of
difficulty in uniting two species, and the degree of sterility of their
hybrid offspring, should generally correspond, though due to distinct
causes; for both depend on the amount of difference of some kind between
the species which are crossed. Nor is it surprising that the facility of
effecting a first cross, the fertility of hybrids produced from it, and the
capacity of being grafted together--though this latter capacity evidently
depends on widely different circumstances--should all run to a certain
extent parallel with the systematic affinity of the forms which are
subjected to experiment; for systematic affinity attempts to express all
kinds of resemblance between all species.
"First crosses between forms known to be varieties, or sufficiently alike
to be considered as varieties, and their mongrel offspring, are very
generally, but not quite universally, fertile. Nor is this nearly general
and perfect fertility surprising, when we remember how liable we are to
argue in a circle with respect to varieties in a state of Nature; and when
we remember that the greater number of varieties have been produced under
domestication by the selection of mere external differences, and not of
differences in the reproductive system. In all other respects, excluding
fertility, there is a close general resemblance between hybrids and
mongrels."--Pp. 276-8.
We fully agree with the general tenor of this weighty passage; but forcible
as are these arguments, and little as the value of fertility or infertility
as a test of species may be, it must not be forgotten that the really
important fact, so far as the inquiry into the origin of species goes, is,
that there are such things in Nature as groups of animals and of plants,
the members of which are incapable of fertile union with those of other
groups; and that there are such things as hybrids, which are absolutely
sterile when crossed with other hybrids. For, if such phænomena as these
were exhibited by only two of those assemblages of living objects, to which
the name of species (whether it be used in its physiological or in its
morphological sense) is given, it would have to be accounted for by any
theory of the origin of species, and every theory which could not account
for it would be, so far, imperfect.
Up to this point, we have been dealing with matters of fact, and the
statements which we have laid before the reader would, to the best of our
knowledge, be admitted to contain a fair exposition of what is at present
known respecting the essential properties of species, by all who have
studied the question. And whatever may be his theoretical views, no
naturalist will probably be disposed to demur to the following summary of
that exposition:--
Living beings, whether animals or plants, are divisible into multitudes of
distinctly definable kinds, which are morphological species. They are also
divisible into groups of individuals, which breed freely together, tending
to reproduce their like, and are physiological species. Normally resembling
their parents, the offspring of members of these species are still liable
to vary; and the variation may be perpetuated by selection, as a race,
which race, in many cases, presents all the characteristics of a
morphological species. But it is not as yet proved that a race ever
exhibits, when crossed with another race of the same species, those
phænomena of hybridisation which are exhibited by many species when crossed
with other species. On the other hand, not only is it not proved that all
species give rise to hybrids infertile _inter se_, but there is much
reason to believe that, in crossing, species exhibit every gradation from
perfect sterility to perfect fertility.
Such are the most essential characteristics of species. Even were man not
one of them--a member of the same system and subject to the same laws--the
question of their origin, their causal connexion, that is, with the other
phænomena of the universe, must have attracted his attention, as soon as
his intelligence had raised itself above the level of his daily wants.
Indeed history relates that such was the case, and has embalmed for us the
speculations upon the origin of living beings, which were among the
earliest products of the dawning intellectual activity of man. In those
early days positive knowledge was not to be had, but the craving after it
needed, at all hazards, to be satisfied, and according to the country, or
the turn of thought, of the speculator, the suggestion that all living
things arose from the mud of the Nile, from a primeval egg, or from some
more anthropomorphic agency, afforded a sufficient resting-place for his
curiosity. The myths of Paganism are as dead as Osiris or Zeus, and the man
who should revive them, in opposition to the knowledge of our time, would
be justly laughed to scorn; but the coeval imaginations current among the
rude inhabitants of Palestine, recorded by writers whose very name and age
are admitted by every scholar to be unknown, have unfortunately not yet
shared their fate, but, even at this day, are regarded by nine-tenths of
the civilised world as the authoritative standard of fact and the criterion
of the justice of scientific conclusions, in all that relates to the origin
of things, and, among them, of species. In this nineteenth century, as at
the dawn of modern physical science, the cosmogony of the semi-barbarous
Hebrew is the incubus of the philosopher and the opprobrium of the
orthodox. Who shall number the patient and earnest seekers after truth,
from the days of Galileo until now, whose lives have been embittered and
their good name blasted by the mistaken zeal of Bibliolaters? Who shall
count the host of weaker men whose sense of truth has been destroyed in the
effort to harmonise impossibilities--whose life has been wasted in the
attempt to force the generous new wine of Science into the old bottles of
Judaism, compelled by the outcry of the same strong party?
It is true that if philosophers have suffered, their cause has been amply
avenged. Extinguished theologians lie about the cradle of every science as
the strangled snakes beside that of Hercules; and history records that
whenever science and orthodoxy have been fairly opposed, the latter has
been forced to retire from the lists, bleeding and crushed if not
annihilated; scotched, if not slain. But orthodoxy is the Bourbon of the
world of thought. It learns not, neither can it forget; and though, at
present, bewildered and afraid to move, it is as willing as ever to insist
that the first chapter of Genesis contains the beginning and the end of
sound science; and to visit, with such petty thunderbolts as its
half-paralysed hands can hurl, those who refuse to degrade Nature to the
level of primitive Judaism.
Philosophers, on the other hand, have no such aggressive tendencies. With
eyes fixed on the noble goal to which "per aspera et ardua" they tend, they
may, now and then, be stirred to momentary wrath by the unnecessary
obstacles with which the ignorant, or the malicious, encumber, if they
cannot bar, the difficult path; but why should their souls be deeply vexed?
The majesty of Fact is on their side, and the elemental forces of Nature
are working for them. Not a star comes to the meridian at its calculated
time but testifies to the justice of their methods--their beliefs are "one
with the falling rain and with the growing corn." By doubt they are
established, and open inquiry is their bosom friend. Such men have no fear
of traditions however venerable, and no respect for them when they become
mischievous and obstructive; but they have better than mere antiquarian
business in hand, and if dogmas, which ought to be fossil but are not, are
not forced upon their notice, they are too happy to treat them as
non-existent.
* * * * *
The hypotheses respecting the origin of species which profess to stand upon
a scientific basis, and, as such, alone demand serious attention, are of
two kinds. The one, the "special creation" hypothesis, presumes every
species to have originated from one or more stocks, these not being the
result of the modification of any other form of living matter--or arising
by natural agencies--but being produced, as such, by a supernatural
creative act.
The other, the so-called "transmutation" hypothesis, considers that all
existing species are the result of the modification of pre-existing
species, and those of their predecessors, by agencies similar to those
which at the present day produce varieties and races, and therefore in an
altogether natural way; and it is a probable, though not a necessary
consequence of this hypothesis, that all living beings have arisen from a
single stock. With respect to the origin of this primitive stock, or
stocks, the doctrine of the origin of species is obviously not necessarily
concerned. The transmutation hypothesis, for example, is perfectly
consistent either with the conception of a special creation of the
primitive germ, or with the supposition of its having arisen, as a
modification of inorganic matter, by natural causes.
The doctrine of special creation owes its existence very largely to the
supposed necessity of making science accord with the Hebrew cosmogony; but
it is curious to observe that, as the doctrine is at present maintained by
men of science, it is as hopelessly inconsistent with the Hebrew view as
any other hypothesis.
If there be any result which has come more clearly out of geological
investigation than another, it is, that the vast series of extinct animals
and plants is not divisible, as it was once supposed to be, into distinct
groups, separated by sharply-marked boundaries. There are no great gulfs
between epochs and formations--no successive periods marked by the
appearance of plants, of water animals, and of land animals, _en
masse_. Every year adds to the list of links between what the older
geologists supposed to be widely separated epochs: witness the crags
linking the drift with older tertiaries; the Maestricht beds linking the
tertiaries with the chalk; the St. Cassian beds exhibiting an abundant
fauna of mixed mesozoic and palaeozoic types, in rocks of an epoch once
supposed to be eminently poor in life; witness, lastly, the incessant
disputes as to whether a given stratum shall be reckoned devonian or
carboniferous, silurian or devonian, cambrian or silurian.
This truth is further illustrated in a most interesting manner by the
impartial and highly competent testimony of M. Pictet, from whose
calculations of what percentage of the genera of animals, existing in any
formation, lived during the preceding formation, it results that in no case
is the proportion less than _one-third_, or 33 per cent. It is the
triassic formation, or the commencement of the mesozoic epoch, which has
received the smallest inheritance from preceding ages. The other formations
not uncommonly exhibit 60, 80, or even 94 per cent, of genera in common
with those whose remains are imbedded in their predecessor. Not only is
this true, but the subdivisions of each formation exhibit new species
characteristic of, and found only in, them; and, in many cases, as in the
lias for example, the separate beds of these subdivisions are distinguished
by well-marked and peculiar forms of life. A section, a hundred feet thick,
will exhibit, at different heights, a dozen species of ammonite, none of
which passes beyond its particular zone of limestone, or clay, into the
zone below it or into that above it; so that those who adopt the doctrine
of special creation must be prepared to admit, that at intervals of time,
corresponding with the thickness of these beds, the Creator thought fit to
interfere with the natural course of events for the purpose of making a new
ammonite. It is not easy to transplant oneself into the frame of mind of
those who can accept such a conclusion as this, on any evidence short of
absolute demonstration; and it is difficult to see what is to be gained by
so doing, since, as we have said, it is obvious that such a view of the
origin of living beings is utterly opposed to the Hebrew cosmogony.
Deserving no aid from the powerful arm of Bibliolatry, then, does the
received form of the hypothesis of special creation derive any support from
science or sound logic? Assuredly not much. The arguments brought forward
in its favour all take one form: If species were not supernaturally
created, we cannot understand the facts _x_, or _y_, or _z_;
we cannot understand the structure of animals or plants, unless we suppose
they were contrived for special ends; we cannot understand the structure of
the eye, except by supposing it to have been made to see with; we cannot
understand instincts, unless we suppose animals to have been miraculously
endowed with them.
As a question of dialectics, it must be admitted that this sort of
reasoning is not very formidable to those who are not to be frightened by
consequences. It is an _argumentum ad ignorantiam_--take this
explanation or be ignorant. But suppose we prefer to admit our ignorance
rather than adopt a hypothesis at variance with all the teachings of
Nature? Or, suppose for a moment we admit the explanation, and then
seriously ask ourselves how much the wiser are we; what does the
explanation explain? Is it any more than a grandiloquent way of announcing
the fact, that we really know nothing about the matter? A phenomenon is
explained when it is shown to be a case of some general law of Nature; but
the supernatural interposition of the Creator can, by the nature of the
case, exemplify no law, and if species have really arisen in this way, it
is absurd to attempt to discuss their origin.
Or, lastly, let us ask ourselves whether any amount of evidence which the
nature of our faculties permits us to attain, can justify us in asserting
that any phenomenon is out of the reach of natural causation. To this end
it is obviously necessary that we should know all the consequences to which
all possible combinations, continued through unlimited time, can give rise.
If we knew these, and found none competent to originate species, we should
have good ground for denying their origin by natural causation. Till we
know them, any hypothesis is better than one which involves us in such
miserable presumption.
But the hypothesis of special creation is not only a mere specious mask for
our ignorance; its existence in Biology marks the youth and imperfection of
the science. For what is the history of every science but the history of
the elimination of the notion of creative, or other interferences, with the
natural order of the phænomena which are the subject-matter of that
science? When Astronomy was young "the morning stars sang together for
joy," and the planets were guided in their courses by celestial hands. Now,
the harmony of the stars has resolved itself into gravitation according to
the inverse squares of the distances, and the orbits of the planets are
deducible from the laws of the forces which allow a schoolboy's stone to
break a window. The lightning was the angel of the Lord; but it has pleased
Providence, in these modern times, that science should make it the humble
messenger of man, and we know that every flash that shimmers about the
horizon on a summer's evening is determined by ascertainable conditions,
and that its direction and brightness might, if our knowledge of these were
great enough, have been calculated.
The solvency of great mercantile companies rests on the validity of the
laws which have been ascertained to govern the seeming irregularity of that
human life which the moralist bewails as the most uncertain of things;
plague, pestilence, and famine are admitted, by all but fools, to be the
natural result of causes for the most part fully within human control, and
not the unavoidable tortures inflicted by wrathful Omnipotence upon His
helpless handiwork.
Harmonious order governing eternally continuous progress--the web and woof
of matter and force interweaving by slow degrees, without a broken thread,
that veil which lies between us and the Infinite--that universe which alone
we know or can know; such is the picture which science draws of the world,
and in proportion as any part of that picture is in unison with the rest,
so may we feel sure that it is rightly painted. Shall Biology alone remain
out of harmony with her sister sciences?
Such arguments against the hypothesis of the direct creation of species as
these are plainly enough deducible from general considerations; but there
are, in addition, phenomena exhibited by species themselves, and yet not so
much a part of their very essence as to have required earlier mention,
which are in the highest degree perplexing, if we adopt the popularly
accepted hypothesis. Such are the facts of distribution in space and in
time; the singular phenomena brought to light by the study of development;
the structural relations of species upon which our systems of
classification are founded; the great doctrines of philosophical anatomy,
such as that of homology, or of the community of structural plan exhibited
by large groups of species differing very widely in their habits and
functions.
The species of animals which inhabit the sea on opposite sides of the
isthmus of Panama are wholly distinct;[Footnote: Recent investigations tend
to show that this statement is not strictly accurate.--1870.] the animals
and plants which inhabit islands are commonly distinct from those of the
neighbouring mainlands, and yet have a similarity of aspect. The mammals of
the latest tertiary epoch in the Old and New Worlds belong to the same
genera, or family groups, as those which now inhabit the same great
geographical area. The crocodilian reptiles which existed in the earliest
secondary epoch were similar in general structure to those now living, but
exhibit slight differences in their vertebræ, nasal passages, and one or
two other points. The guinea-pig has teeth which are shed before it is
born, and hence can never subserve the masticatory purpose for which they
seem contrived, and, in like manner, the female dugong has tusks which
never cut the gum. All the members of the same great group run through
similar conditions in their development, and all their parts, in the adult
state, are arranged according to the same plan. Man is more like a gorilla
than a gorilla is like a lemur. Such are a few, taken at random, among the
multitudes of similar facts which modern research has established; but when
the student seeks for an explanation of them from the supporters of the
received hypothesis of the origin of species, the reply he receives is, in
substance, of Oriental simplicity and brevity--"Mashallah! it so pleases
God!" There are different species on opposite sides of the isthmus of
Panama, because they were created different on the two sides. The pliocene
mammals are like the existing ones, because such was the plan of creation;
and we find rudimental organs and similarity of plan, because it has
pleased the Creator to set before Himself a "divine exemplar or archetype,"
and to copy it in His works; and somewhat ill, those who hold this view
imply, in some of them. That such verbal hocus-pocus should be received as
science will one day be regarded as evidence of the low state of
intelligence in the nineteenth century, just as we amuse ourselves with the
phraseology about Nature's abhorrence of a vacuum, wherewith Torricellis
compatriots were satisfied to explain the rise of water in a pump. And be
it recollected that this sort of satisfaction works not only negative but
positive ill, by discouraging inquiry, and so depriving man of the usufruct
of one of the most fertile fields of his great patrimony, Nature.
The objections to the doctrine of the origin of species by special creation
which have been detailed, must have occurred, with more or less force, to
the mind of every one who has seriously and independently considered the
subject. It is therefore no wonder that, from time to time, this hypothesis
should have been met by counter hypotheses, all as well, and some better
founded than itself; and it is curious to remark that the inventors of the
opposing views seem to have been led into them as much by their knowledge
of geology, as by their acquaintance with biology. In fact, when the mind
has once admitted the conception of the gradual production of the present
physical state of our globe, by natural causes operating through long ages
of time, it will be little disposed to allow that living beings have made
their appearance in another way, and the speculations of De Maillet and his
successors are the natural complement of Scilla's demonstration of the true
nature of fossils.
A contemporary of Newton and of Leibnitz, sharing therefore in the
intellectual activity of the remarkable age which witnessed the birth of
modern physical science, Benoît de Maillet spent a long life as a consular
agent of the French Government in various Mediterranean ports. For sixteen
years, in fact, he held the office of Consul-General in Egypt, and the
wonderful phenomena offered by the valley of the Nile appear to have
strongly impressed his mind, to have directed his attention to all facts of
a similar order which came within his observation, and to have led him to
speculate on the origin of the present condition of our globe and of its
inhabitants. But, with all his ardour for science, De Maillet seems to have
hesitated to publish views which, notwithstanding the ingenious attempts to
reconcile them with the Hebrew hypothesis contained in the preface to
"Telliamed," were hardly likely to be received with favour by his
contemporaries.
But a short time had elapsed since more than one of the great anatomists
and physicists of the Italian school had paid dearly for their endeavours
to dissipate some of the prevalent errors; and their illustrious pupil,
Harvey, the founder of modern physiology, had not fared so well, in a
country less oppressed by the benumbing influences of theology, as to tempt
any man to follow his example. Probably not uninfluenced by these
considerations, his Catholic majesty's Consul-General for Egypt kept his
theories to himself throughout a long life, for "Telliamed," the only
scientific work which is known to have proceeded from his pen, was not
printed till 1735, when its author had reached the ripe age of
seventy-nine; and though De Maillet lived three years longer, his book was
not given to the world before 1748. Even then it was anonymous to those who
were not in the secret of the anagrammatic character of its title; and the
preface and dedication are so worded as, in case of necessity, to give the
printer a fair chance of falling back on the excuse that the work was
intended for a mere _jeu d'esprit_.
The speculations of the suppositious Indian sage, though quite as sound as
those of many a "Mosaic Geology," which sells exceedingly well, have no
great value if we consider them by the light of modern science. The waters
are supposed to have originally covered the whole globe; to have deposited
the rocky masses which compose its mountains by processes comparable to
those which are now forming mud, sand, and shingle; and then to have
gradually lowered their level, leaving the spoils of their animal and
vegetable inhabitants embedded in the strata. As the dry land appeared,
certain of the aquatic animals are supposed to have taken to it, and to
have become gradually adapted to terrestrial and aërial modes of existence.
But if we regard the general tenor and style of the reasoning in relation
to the state of knowledge of the day, two circumstances appear very well
worthy of remark. The first, that De Maillet had a notion of the
modifiability of living forms (though without any precise information on
the subject), and how such modifiability might account for the origin of
species; the second, that he very clearly apprehended the great modern
geological doctrine, so strongly insisted upon by Hutton, and so ably and
comprehensively expounded by Lyell, that we must look to existing causes
for the explanation of past geological events. Indeed, the following
passage of the preface, in which De Maillet is supposed to speak of the
Indian philosopher Telliamed, his _alter ego,_ might have been written
by the most philosophical uniformitarian of the present day:--
"Ce qu'il y a d'étonnant, est que pour arriver à ces connaissances il
semble avoir perverti l'ordre naturel, puisqu'au lieu de s'attacher d'abord
à rechercher l'origine de notre globe il a commence par travailler à
s'instruire de la nature. Mais à l'entendre, ce renversement de l'ordre a
été pour lui l'effet d'un génie favorable qui l'a conduit pas à pas et
comme par la main aux découvertes les plus sublimes. C'est en décomposant
la substance de ce globe par tine anatomie exacte de toutes ses parties
qu'il a premierement appris de quelles matières il était composé et quels
arrangemens ces mêmes matières observaient entre elles. Ces lumieres
jointes à l'esprit de comparaison toujours nécessaire à quiconque
entreprend de percer les voiles dont la nature aime à se cacher, ont servi
de guide à notre philosophe pour parvenir à des connoissances plus
intéressantes. Par la matière et l'arrangement de ces compositions il
prétend avoir reconnu quelle est la véritable origine de ce globe que nous
habitons, comment et par qui il a été formé."-Pp. xix. xx.
But De Maillet was before his age, and as could hardly fail to happen to
one who speculated on a zoological and botanical question before Linnæus,
and on a physiological problem before Haller, he fell into great errors
here and there; and hence, perhaps, the general neglect of his work.
Robinet's speculations are rather behind, than in advance of, those of De
Maillet; and though Linnæus may have played with the hypothesis of
transmutation, it obtained no serious support until Lamarck adopted it, and
advocated it with great ability in his "Philosophie Zoologique."
Impelled towards the hypothesis of the transmutation of species, partly by
his general cosmological and geological views; partly by the conception of
a graduated, though irregularly branching, scale of being, which had arisen
out of his profound study of plants and of the lower forms of animal life,
Lamarck, whose general line of thought often closely resembles that of De
Maillet, made a great advance upon the crude and merely speculative manner
in which that writer deals with the question of the origin of living
beings, by endeavouring to find physical causes competent to effect that
change of one species into another, which De Maillet had only supposed to
occur. And Lamarck conceived that he had found in Nature such causes, amply
sufficient for the purpose in view. It is a physiological fact, he says,
that organs are increased in size by action, atrophied by inaction; it is
another physiological fact that modifications produced are transmissible to
offspring. Change the actions of an animal, therefore, and you will change
its structure, by increasing the development of the parts newly brought
into use and by the diminution of those less used; but by altering the
circumstances which surround it you will alter its actions, and hence, in
the long run, change of circumstance must produce change of organisation.
All the species of animals, therefore, are, in Lamarck's view, the result
of the indirect action of changes of circumstance, upon those primitive
germs which he considered to have originally arisen, by spontaneous
generation, within the waters of the globe. It is curious, however, that
Lamarck should insist so strongly [Footnote: See _Phil. Zoologique_,
vol. i. p. 222. et seq.] as he has done, that circumstances never in any
degree directly modify the form or the organisation of animals, but only
operate by changing their wants and consequently their actions; for he
thereby brings upon himself the obvious question, How, then, do plants,
which cannot be said to have wants or actions, become modified? To this he
replies, that they are modified by the changes in their nutritive
processes, which are effected by changing circumstances; and it does not
seem to have occurred to him that such changes might be as well supposed to
take place among animals.
When we have said that Lamarck felt that mere speculation was not the way
to arrive at the origin of species, but that it was necessary, in order to
the establishment of any sound theory on the subject, to discover by
observation or otherwise, some _vera causa_, competent to give rise to
them; that he affirmed the true order of classification to coincide with
the order of their development one from another; that he insisted on the
necessity of allowing sufficient time, very strongly; and that all the
varieties of instinct and reason were traced back by him to the same cause
as that which has given rise to species, we have enumerated his chief
contributions to the advance of the question. On the other hand, from his
ignorance of any power in Nature competent to modify the structure of
animals, except the development of parts, or atrophy of them, in
consequence of a change of needs, Lamarck was led to attach infinitely
greater weight than it deserves to this agency, and the absurdities into
which he was led have met with deserved condemnation. Of the struggle for
existence, on which, as we shall see, Mr. Darwin lays such great stress, he
had no conception; indeed, he doubts whether there really are such things
as extinct species, unless they be such large animals as may have met their
death at the hands of man; and so little does he dream of there being any
other destructive causes at work, that, in discussing the possible
existence of fossil shells, he asks, "Pourquoi d'ailleurs seroient-ils
perdues dès que l'homme n'a pu opérer leur destruction?" ("Phil. Zool.,"
vol. i. p. 77.) Of the influence of selection Lamarck has as little notion,
and he makes no use of the wonderful phenomena which are exhibited by
domesticated animals, and illustrate its powers. The vast influence of
Cuvier was employed against the Lamarckian views, and, as the untenability
of some of his conclusions was easily shown, his doctrines sank under the
opprobrium of scientific, as well as of theological, heterodoxy. Nor have
the efforts made of late years to revive them tended to re-establish their
credit in the minds of sound thinkers acquainted with the facts of the
case; indeed it may be doubted whether Lamarck has not suffered more from
his friends than from his foes.
Two years ago, in fact, though we venture to question if even the strongest
supporters of the special creation hypothesis had not, now and then, an
uneasy consciousness that all was not right, their position seemed more
impregnable than ever, if not by its own inherent strength, at any rate by
the obvious failure of all the attempts which had been made to carry it. On
the other hand, however much the few, who thought deeply on the question of
species, might be repelled by the generally received dogmas, they saw no
way of escaping from them save by the adoption of suppositions so little
justified by experiment or by observation as to be at least equally
distasteful.
The choice lay between two absurdities and a middle condition of uneasy
scepticism; which last, however unpleasant and unsatisfactory, was
obviously the only justifiable state of mind under the circumstances.
Such being the general ferment in the minds of naturalists, it is no wonder
that they mustered strong in the rooms of the Linnæan Society, on the 1st
of July of the year 1858, to hear two papers by authors living on opposite
sides of the globe, working out their results independently, and yet
professing to have discovered one and the same solution of all the problems
connected with species. The one of these authors was an able naturalist,
Mr. Wallace, who had been employed for some years in studying the
productions of the islands of the Indian Archipelago, and who had forwarded
a memoir embodying his views to Mr. Darwin, for communication to the
Linnæan Society. On perusing the essay, Mr. Darwin was not a little
surprised to find that it embodied some of the leading ideas of a great
work which he had been preparing for twenty years, and parts of which,
containing a development of the very same views, had been perused by his
private friends fifteen or sixteen years before. Perplexed in what manner
to do full justice both to his friend and to himself, Mr. Darwin placed the
matter in the hands of Dr. Hooker and Sir Charles Lyell, by whose advice he
communicated a brief abstract of his own views to the Linnæan Society, at
the same time that Mr. Wallace's paper was read. Of that abstract, the work
on the "Origin of Species" is an enlargement; but a complete statement of
Mr. Darwin's doctrine is looked for in the large and well-illustrated work
which he is said to be preparing for publication.
The Darwinian hypothesis has the merit of being eminently simple and
comprehensible in principle, and its essential positions may be stated in a
very few words: all species have been produced by the development of
varieties from common stocks; by the conversion of these, first into
permanent races and then into new species, by the process of _natural
selection_, which process is essentially identical with that artificial
selection by which man has originated the races of domestic animals--the
_struggle for existence_ taking the place of man, and exerting, in the
case of natural selection, that selective action which he performs in
artificial selection.
The evidence brought forward by Mr. Darwin in support of his hypothesis is
of three kinds. First, he endeavours to prove that species may be
originated by selection; secondly, he attempts to show that natural causes
are competent to exert selection; and thirdly, he tries to prove that the
most remarkable and apparently anomalous phænomena exhibited by the
distribution, development, and mutual relations of species, can be shown to
be deducible from the general doctrine of their origin, which he propounds,
combined with the known facts of geological change; and that, even if all
these phænomena are not at present explicable by it, none are necessarily
inconsistent with it.
There cannot be a doubt that the method of inquiry which Mr. Darwin has
adopted is not only rigorously in accordance with the canons of scientific
logic, but that it is the only adequate method. Critics exclusively trained
in classics or in mathematics, who have never determined a scientific fact
in their lives by induction from experiment or observation, prate learnedly
about Mr. Darwin's method, which is not inductive enough, not Baconian
enough, forsooth, for them. But even if practical acquaintance with the
process of scientific investigation is denied them, they may learn, by the
perusal of Mr. Mill's admirable chapter "On the Deductive Method," that
there are multitudes of scientific inquiries in which the method of pure
induction helps the investigator but a very little way.
"The mode of investigation," says Mr. Mill, "which, from the proved
inapplicability of direct methods of observation and experiment, remains to
us as the main source of the knowledge we possess, or can acquire,
respecting the conditions and laws of recurrence of the more complex
phænomena, is called, in its most general expression, the deductive method,
and consists of three operations: the first, one of direct induction; the
second, of ratiocination; and the third, of verification."
Now, the conditions which have determined the existence of species are not
only exceedingly complex, but, so far as the great majority of them are
concerned, are necessarily beyond our cognisance. But what Mr. Darwin has
attempted to do is in exact accordance with the rule laid down by Mr. Mill;
he has endeavoured to determine certain great facts inductively, by
observation and experiment; he has then reasoned from the data thus
furnished; and lastly, he has tested the validity of his ratiocination by
comparing his deductions with the observed facts of Nature. Inductively,
Mr. Darwin endeavours to prove that species arise in a given way.
Deductively, he desires to show that, if they arise in that way, the facts
of distribution, development, classification, &c., may be accounted for,
_i.e._ may be deduced from their mode of origin, combined with
admitted changes in physical geography and climate, during an indefinite
period. And this explanation, or coincidence of observed with deduced
facts, is, so far as it extends, a verification of the Darwinian view.
There is no fault to be found with Mr. Darwin's method, then; but it is
another question whether he has fulfilled all the conditions imposed by
that method. Is it satisfactorily proved, in fact, that species may be
originated by selection? that there is such a thing as natural selection?
that none of the phænomena exhibited by species are inconsistent with the
origin of species in this way? If these questions can be answered in the
affirmative, Mr. Darwin's view steps out of the rank of hypotheses into
those of proved theories; but, so long as the evidence at present adduced
falls short of enforcing that affirmation, so long, to our minds, must the
new doctrine be content to remain among the former--an extremely valuable,
and in the highest degree probable, doctrine, indeed the only extant
hypothesis which is worth anything in a scientific point of view; but still
a hypothesis, and not yet the theory of species.
After much consideration, and with assuredly no bias against Mr. Darwin's
views, it is our clear conviction that, as the evidence stands, it is not
absolutely proven that a group of animals, having all the characters
exhibited by species in Nature, has ever been originated by selection,
whether artificial or natural. Groups having the morphological character of
species--distinct and permanent races in fact--have been so produced over
and over again; but there is no positive evidence, at present, that any
group of animals has, by variation and selective breeding, given rise to
another group which was, even in the least degree, infertile with the
first. Mr. Darwin is perfectly aware of this weak point, and brings forward
a multitude of ingenious and important arguments to diminish the force of
the objection. We admit the value of these arguments to their fullest
extent; nay, we will go so far as to express our belief that experiments,
conducted by a skilful physiologist, would very probably obtain the desired
production of mutually more or less infertile breeds from a common stock,
in a comparatively few years; but still, as the case stands at present,
this "little rift within the lute" is not to be disguised nor overlooked.
In the remainder of Mr. Darwin's argument our own private ingenuity has not
hitherto enabled us to pick holes of any great importance; and judging by
what we hear and read, other adventurers in the same field do not seem to
have been much more fortunate. It has been urged, for instance, that in his
chapters on the struggle for existence and on natural selection, Mr. Darwin
does not so much prove that natural selection does occur, as that it must
occur; but, in fact, no other sort of demonstration is attainable. A race
does not attract our attention in Nature until it has, in all probability,
existed for a considerable time, and then it is too late to inquire into
the conditions of its origin. Again, it is said that there is no real
analogy between the selection which takes place under domestication, by
human influence, and any operation which can be effected by Nature, for man
interferes intelligently. Reduced to its elements, this argument implies
that an effect produced with trouble by an intelligent agent must, _à
fortiori,_ be more troublesome, if not impossible, to an unintelligent
agent. Even putting aside the question whether Nature, acting as she does
according to definite and invariable laws, can be rightly called an
unintelligent agent, such a position as this is wholly untenable. Mix salt
and sand, and it shall puzzle the wisest of men, with his mere natural
appliances, to separate all the grains of sand from all the grains of salt;
but a shower of rain will effect the same object in ten minutes. And so,
while man may find it tax all his intelligence to separate any variety
which arises, and to breed selectively from it, the destructive agencies
incessantly at work in Nature, if they find one variety to be more soluble
in circumstances than the other, will inevitably, in the long run,
eliminate it.
A frequent and a just objection to the Lamarckian hypothesis of the
transmutation of species is based upon the absence of transitional forms
between many species. But against the Darwinian hypothesis this argument
has no force. Indeed, one of the most valuable and suggestive parts of Mr.
Darwin's work is that in which he proves, that the frequent absence of
transitions is a necessary consequence of his doctrine, and that the stock
whence two or more species have sprung, need in no respect be intermediate
between these species. If any two species have arisen from a common stock
in the same way as the carrier and the pouter, say, have arisen from the
rock-pigeon, then the common stock of these two species need be no more
intermediate between the two than the rock-pigeon is between the carrier
and pouter. Clearly appreciate the force of this analogy, and all the
arguments against the origin of species by selection, based on the absence
of transitional forms, fall to the ground. And Mr. Darwin's position might,
we think, have been even stronger than it is if he had not embarrassed
himself with the aphorism, "_Natura non facit saltum_," which turns up
so often in his pages. We believe, as we have said above, that Nature does
make jumps now and then, and a recognition of the fact is of no small
importance in disposing of many minor objections to the doctrine of
transmutation.
But we must pause. The discussion of Mr. Darwin's arguments in detail would
lead us far beyond the limits within which we proposed, at starting, to
confine this article. Our object has been attained if we have given an
intelligible, however brief, account of the established facts connected
with species, and of the relation of the explanation of those facts offered
by Mr. Darwin to the theoretical views held by his predecessors and his
contemporaries, and, above all, to the requirements of scientific logic. We
have ventured to point out that it does not, as yet, satisfy all those
requirements; but we do not hesitate to assert that it is as superior to
any preceding or contemporary hypothesis, in the extent of observational
and experimental basis on which it rests, in its rigorously scientific
method, and in its power of explaining biological phenomena, as was the
hypothesis of Copernicus to the speculations of Ptolemy. But the planetary
orbits turned out to be not quite circular after all, and, grand as was the
service Copernicus rendered to science, Kepler and Newton had to come after
him. What if the orbit of Darwinism should be a little too circular? What
if species should offer residual phænomena, here and there, not explicable
by natural selection? Twenty years hence naturalists may be in a position
to say whether this is, or is not, the case; but in either event they will
owe the author of "The Origin of Species" an immense debt of gratitude. We
should leave a very wrong impression on the reader's mind if we permitted
him to suppose that the value of that work depends wholly on the ultimate
justification of the theoretical views which it contains. On the contrary,
if they were disproved to-morrow, the book would still be the best of its
kind--the most compendious statement of well-sifted facts bearing on the
doctrine of species that has ever appeared. The chapters on Variation, on
the Struggle for Existence, on Instinct, on Hybridism, on the Imperfection
of the Geological Record, on Geographical Distribution, have not only no
equals, but, so far as our knowledge goes, no competitors, within the range
of biological literature. And viewed as a whole, we do not believe that,
since the publication of Von Baer's "Researches on Development," thirty
years ago, any work has appeared calculated to exert so large an influence,
not only on the future of Biology, but in extending the domination of
Science over regions of thought into which she has, as yet, hardly
penetrated.
III
CRITICISMS ON "THE ORIGIN OF SPECIES"
[1864]
1. UEBER DIE DARWIN'SCHE SCHÖPFUNGSTHEORIE; EIN VORTRAG, Von A. KÖLLIKER.
Leipzig, 1864.
2. EXAMINATION DU LIVRE DE M. DARWIN SUR L'ORIGINE DES ESPÈCES. Par P.
FLOURENS. Paris, 1864.
In the course of the present year several foreign commentaries upon Mr.
Darwin's great work have made their appearance. Those who have perused that
remarkable chapter of the "Antiquity of Man," in which Sir Charles Lyell
draws a parallel between the development of species and that of languages,
will be glad to hear that one of the most eminent philologers of Germany,
Professor Schleicher, has, independently, published a most instructive and
philosophical pamphlet (an excellent notice of which is to be found in the
_Reader_, for February 27th of this year) supporting similar views
with all the weight of his special knowledge and established authority as a
linguist. Professor Haeckel, to whom Schleicher addresses himself,
previously took occasion, in his splendid monograph on the
_Radiolaria_,[Footnote: _Die Radiolarien: eine Monographie_, p.
231.] to express his high appreciation of, and general concordance with,
Mr. Darwin's views.
But the most elaborate criticisms of the "Origin of Species" which have
appeared are two works of very widely different merit, the one by Professor
Kölliker, the well-known anatomist and histologist of Würzburg; the other
by M. Flourens, Perpetual Secretary of the French Academy of Sciences.
Professor Kölliker's critical essay "Upon the Darwinian Theory" is, like
all that proceeds from the pen of that thoughtful and accomplished writer,
worthy of the most careful consideration. It comprises a brief but clear
sketch of Darwin's views, followed by an enumeration of the leading
difficulties in the way of their acceptance; difficulties which would
appear to be insurmountable to Professor Kölliker, inasmuch as he proposes
to replace Mr. Darwin's Theory by one which he terms the "Theory of
Heterogeneous Generation." We shall proceed to consider first the
destructive, and secondly, the constructive portion of the essay.
We regret to find ourselves compelled to dissent very widely from many of
Professor Kölliker's remarks; and from none more thoroughly than from those
in which he seeks to define what we may term the philosophical position of
Darwinism.
"Darwin," says Professor Kölliker, "is, in the fullest sense of the word, a
Teleologist. He says quite distinctly (First Edition, pp. 199, 200) that
every particular in the structure of an animal has been created for its
benefit, and he regards the whole series of animal forms only from this
point of view."
And again:
"7. The teleological general conception adopted by Darwin is a mistaken
one.
"Varieties arise irrespectively of the notion of purpose, or of utility,
according to general laws of Nature, and may be either useful, or hurtful,
or indifferent.
"The assumption that an organism exists only on account of some definite
end in view, and represents something more than the incorporation of a
general idea, or law, implies a one-sided conception of the universe.
Assuredly, every organ has, and every organism fulfils, its end, but its
purpose is not the condition of its existence. Every organism is also
sufficiently perfect for the purpose it serves, and in that, at least, it
is useless to seek for a cause of its improvement."
It is singular how differently one and the same book will impress different
minds. That which struck the present writer most forcibly on his first
perusal of the "Origin of Species" was the conviction that Teleology, as
commonly understood, had received its deathblow at Mr. Darwin's hands. For
the teleological argument runs thus: an organ or organism (A) is precisely
fitted to perform a function or purpose (B); therefore it was specially
constructed to perform that function. In Paley's famous illustration, the
adaptation of all the parts of the watch to the function, or purpose, of
showing the time, is held to be evidence that the watch was specially
contrived to that end; on the ground, that the only cause we know of,
competent to produce such an effect as a watch which shall keep time, is a
contriving intelligence adapting the means directly to that end.
Suppose, however, that any one had been able to show that the watch had not
been made directly by any person, but that it was the result of the
modification of another watch which kept time but poorly; and that this
again had proceeded from a structure which could hardly be called a watch
at all--seeing that it had no figures on the dial and the hands were
rudimentary; and that going back and back in time we came at last to a
revolving barrel as the earliest traceable rudiment of the whole fabric.
And imagine that it had been possible to show that all these changes had
resulted, first, from a tendency of the structure to vary indefinitely; and
secondly, from something in the surrounding world which helped all
variations in the direction of an accurate time-keeper, and checked all
those in other directions; then it is obvious that the force of Paley's
argument would be gone. For it would be demonstrated that an apparatus
thoroughly well adapted to a particular purpose might be the result of a
method of trial and error worked by unintelligent agents, as well as of the
direct application of the means appropriate to that end, by an intelligent
agent.
Now it appears to us that what we have here, for illustration's sake,
supposed to be done with the watch, is exactly what the establishment of
Darwin's Theory will do for the organic world. For the notion that every
organism has been created as it is and launched straight at a purpose, Mr.
Darwin substitutes the conception of something which may fairly be termed a
method of trial and error. Organisms vary incessantly; of these variations
the few meet with surrounding conditions which suit them and thrive; the
many are unsuited and become extinguished.
According to Teleology, each organism is like a rifle bullet fired straight
at a mark; according to Darwin, organisms are like grapeshot of which one
hits something and the rest fall wide.
For the teleologist an organism exists because it was made for the
conditions in which it is found; for the Darwinian an organism exists
because, out of many of its kind, it is the only one which has been able to
persist in the conditions in which it is found.
Teleology implies that the organs of every organism are perfect and cannot
be improved; the Darwinian theory simply affirms that they work well enough
to enable the organism to hold its own against such competitors as it has
met with, but admits the possibility of indefinite improvement. But an
example may bring into clearer light the profound opposition between the
ordinary teleological, and the Darwinian, conception.
Cats catch mice, small birds and the like, very well. Teleology tells us
that they do so because they were expressly constructed for so doing--that
they are perfect mousing apparatuses, so perfect and so delicately adjusted
that no one of their organs could be altered, without the change involving
the alteration of all the rest. Darwinism affirms on the contrary, that
there was no express construction concerned in the matter; but that among
the multitudinous variations of the Feline stock, many of which died out
from want of power to resist opposing influences, some, the cats, were
better fitted to catch mice than others, whence they throve and persisted,
in proportion to the advantage over their fellows thus offered to them.
Far from imagining that cats exist _in order_ to catch mice well,
Darwinism supposes that cats exist because they catch mice well--mousing
being not the end, but the condition, of their existence. And if the cat
type has long persisted as we know it, the interpretation of the fact upon
Darwinian principles would be, not that the cats have remained invariable,
but that such varieties as have incessantly occurred have been, on the
whole, less fitted to get on in the world than the existing stock.
If we apprehend the spirit of the "Origin of Species" rightly, then,
nothing can be more entirely and absolutely opposed to Teleology, as it is
commonly understood, than the Darwinian Theory. So far from being a
"Teleologist in the fullest sense of the word," we should deny that he is a
Teleologist in the ordinary sense at all; and we should say that, apart
from his merits as a naturalist, he has rendered a most remarkable service
to philosophical thought by enabling the student of Nature to recognise, to
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