The Origin of Species
by
Thomas H. Huxley
This etext was prepared by Amy E. Zelmer.
This etext is based on^M
http://aleph0.clarku.edu/huxley/CE2/OrS.html^M
THE ORIGIN OF SPECIES*
by Thomas H. Huxley
[footnote] *'The Westminster Review', April 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wholly superseded the ambition and the vanity of the carnal man within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 '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*, "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."
[footnote] *On the Osteology of the Chimpanzees and Orangs:
Transactions of the Zoological Society, 1858.
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" 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 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.* 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.
[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, Pt. I. pp. 89, 90.
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* the animals and plants which
inhabit islands are commonly distinct from those of the neighbouring
mainlands, and yet have a similarity of aspect.
[footnote] *Recent investigations tend to show that this
statement is not strictly accurate.--1870.
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*
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.
[footnote] *See 'Phil. Zoologique,' vol. i. p. 222, 'et seq.'
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.
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