THE ORIGIN OF SPECIES

From ‘The Westminster Review’, April 1860.

[1]

By Thomas H. Huxley

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superseded the ambition and the vanity of the carnal man within him, he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 ‘litterateur’ 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, or 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 2, “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 exuvia; 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. 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 Archaeus 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 phenomena of vitality are not something apart from other physical
phenomena, 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 whose members 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” he 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 Reaumur, in his ‘Art de faire eclore 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, 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 pre-potent 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, Andre, 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 Andre 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. 3 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, whose skeleton 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 grandchildren 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 condition; 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 whose transmission 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-Sequard, 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.

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 Dr. 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 vertebrae
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 phenomena
of hybridization—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 only 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 the same 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 superadded 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 hybridization 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’, whose male element will fertilize 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 organization 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, whose members 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 phenomena 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
phenomena of hybridization 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
phenomena 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 civilized 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 harmonize
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 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 phenomena 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 4 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 vertebrae, 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
Torricelli’s 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, Benoit 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 aerial 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’etonnant, est que pour arriver a ces connoissances il
semble avoir perverti l’ordre naturel, puisqu’au lieu de s’attacher
d’abord a rechercher l’origine de notre globe il a commence par travailler
a s’instruire de la nature. Mais a l’entendre, ce renversement de l’ordre
a ete pour lui l’effet d’un genie favorable qui l’a conduit pas a pas et
comme par la main aux decouvertes les plus sublimes. C’est en decomposant
la substance de ce globe par une anatomie exacte de toutes ses parties
qu’il a premierement appris de quelles matieres il etait compose et quels
arrangemens ces memes matieres observaient entre elles. Ces lumieres
jointes a l’esprit de comparaison toujours necessaire a quiconque
entreprend de percer les voiles dont la nature aime a se cacher, ont servi
de guide a notre philosophe pour parvenir a des connoissances plus
interessantes. Par la matiere et l’arrangement de ces compositions il
pretend avoir reconnu quelle est la veritable origine de ce globe que nous
habitons, comment et par qui il a ete forme.”—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 Linnaeus,
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 Linnaeus 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 organization. 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 5 as he has done, that circumstances
never in any degree directly modify the form or the organization 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 des que l’homme n’a pu operer 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 Linnaean 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 Linnaean 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 Linnaean
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 phenomena 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 phenomena 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
phenomena, 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 cognizance. 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, etc., 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 phenomena 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 originate 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, ‘a 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 phenomena, 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.

1 (return)
[ ‘The Westminster Review’,
April 1860.]

2 (return)
[ On the Osteology of the
Chimpanzees and Orangs: Transactions of the Zoological Society, 1858.]

3 (return)
[ 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, Pt. I. pp. 89, 90.]

4 (return)
[ Recent investigations tend
to show that this statement is not strictly accurate.—1870.]

5 (return)
[ See ‘Phil. Zoologique,’
vol. i. p. 222, ‘et seq.’]