A Critical Examination of On The Origin of Species
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Thomas H. Huxley >> A Critical Examination of On The Origin of Species
This etext was prepared by Amy E. Zelmer.
A CRITICAL EXAMINATION OF THE POSITION OF MR. DARWIN'S WORK, "ON
THE ORIGIN OF SPECIES," IN RELATION TO THE COMPLETE THEORY OF THE
CAUSES OF THE PHENOMENA OF ORGANIC NATURE
by Thomas H. Huxley
IN the preceding five lectures I have endeavoured to give you an account
of those facts, and of those reasonings from facts, which form the data
upon which all theories regarding the causes of the phenomena of
organic nature must be based. And, although I have had frequent
occasion to quote Mr. Darwin--as all persons hereafter, in speaking upon
these subjects, will have occasion to quote his famous book on the
"Origin of Species,"--you must yet remember that, wherever I have
quoted him, it has not been upon theoretical points, or for statements
in any way connected with his particular speculations, but on matters
of fact, brought forward by himself, or collected by himself, and which
appear incidentally in his book. If a man 'will' make a book,
professing to discuss a single question, an encyclopaedia, I cannot help
it.
Now, having had an opportunity of considering in this sort of way the
different statements bearing upon all theories whatsoever, I have to
lay before you, as fairly as I can, what is Mr. Darwin's view of the
matter and what position his theories hold, when judged by the
principles which I have previously laid down, as deciding our judgments
upon all theories and hypotheses.
I have already stated to you that the inquiry respecting the causes of
the phenomena of organic nature resolves itself into two problems--the
first being the question of the origination of living or organic
beings; and the second being the totally distinct problem of the
modification and perpetuation of organic beings when they have already
come into existence. The first question Mr. Darwin does not touch; he
does not deal with it at all; but he says--given the origin of organic
matter--supposing its creation to have already taken place, my object is
to show in consequence of what laws and what demonstrable properties of
organic matter, and of its environments, such states of organic nature
as those with which we are acquainted must have come about. This, you
will observe, is a perfectly legitimate proposition; every person has a
right to define the limits of the inquiry which he sets before himself;
and yet it is a most singular thing that in all the multifarious, and,
not unfrequently, ignorant attacks which have been made upon the
'Origin of Species', there is nothing which has been more speciously
criticised than this particular limitation. If people have nothing else
to urge against the book, they say--"Well, after all, you see, Mr.
Darwin's explanation of the 'Origin of Species' is not good for much,
because, in the long run, he admits that he does not know how organic
matter began to exist. But if you admit any special creation for the
first particle of organic matter you may just as well admit it for all
the rest; five hundred or five thousand distinct creations are just as
intelligible, and just as little difficult to understand, as one." The
answer to these cavils is two-fold. In the first place, all human
inquiry must stop somewhere; all our knowledge and all our
investigation cannot take us beyond the limits set by the finite and
restricted character of our faculties, or destroy the endless unknown,
which accompanies, like its shadow, the endless procession of
phenomena. So far as I can venture to offer an opinion on such a
matter, the purpose of our being in existence, the highest object that
human beings can set before themselves, is not the pursuit of any such
chimera as the annihilation of the unknown; but it is simply the
unwearied endeavour to remove its boundaries a little further from our
little sphere of action.
I wonder if any historian would for a moment admit the objection, that
it is preposterous to trouble ourselves about the history of the Roman
Empire, because we do not know anything positive about the origin and
first building of the city of Rome! Would it be a fair objection to
urge, respecting the sublime discoveries of a Newton, or a Kepler, those
great philosophers, whose discoveries have been of the profoundest
benefit and service to all men,--to say to them--"After all that you
have told us as to how the planets revolve, and how they are maintained
in their orbits, you cannot tell us what is the cause of the origin of
the sun, moon, and stars. So what is the use of what you have done?"
Yet these objections would not be one whit more preposterous than the
objections which have been made to the 'Origin of Species.' Mr. Darwin,
then, had a perfect right to limit his inquiry as he pleased, and the
only question for us--the inquiry being so limited--is to ascertain
whether the method of his inquiry is sound or unsound; whether he has
obeyed the canons which must guide and govern all investigation, or
whether he has broken them; and it was because our inquiry this evening
is essentially limited to that question, that I spent a good deal of
time in a former lecture (which, perhaps, some of you thought might
have been better employed), in endeavouring to illustrate the method
and nature of scientific inquiry in general. We shall now have to put
in practice the principles that I then laid down.
I stated to you in substance, if not in words, that wherever there are
complex masses of phenomena to be inquired into, whether they be
phenomena of the affairs of daily life, or whether they belong to the
more abstruse and difficult problems laid before the philosopher, our
course of proceeding in unravelling that complex chain of phenomena with
a view to get at its cause, is always the same; in all cases we must
invent an hypothesis; we must place before ourselves some more or less
likely supposition respecting that cause; and then, having assumed an
hypothesis, having supposed cause for the phenomena in question, we must
endeavour, on the one hand, to demonstrate our hypothesis, or, on the
other, to upset and reject it altogether, by testing it in three ways.
We must, in the first place, be prepared to prove that the supposed
causes of the phenomena exist in nature; that they are what the
logicians call 'vera causae'--true causes;--in the next place, we
should be prepared to show that the assumed causes of the phenomena are
competent to produce such phenomena as those which we wish to explain
by them; and in the last place, we ought to be able to show that no
other known causes are competent to produce those phenomena. If we can
succeed in satisfying these three conditions we shall have demonstrated
our hypothesis; or rather I ought to say we shall have proved it as far
as certainty is possible for us; for, after all, there is no one of our
surest convictions which may not be upset, or at any rate modified by a
further accession of knowledge. It was because it satisfied these
conditions that we accepted the hypothesis as to the disappearance of
the tea-pot and spoons in the case I supposed in a previous lecture; we
found that our hypothesis on that subject was tenable and valid, because
the supposed cause existed in nature, because it was competent to
account for the phenomena, and because no other known cause was
competent to account for them; and it is upon similar grounds that any
hypothesis you choose to name is accepted in science as tenable and
valid.
What is Mr. Darwin's hypothesis? As I apprehend it--for I have put it
into a shape more convenient for common purposes than I could find
'verbatim' in his book--as I apprehend it, I say, it is, that all the
phenomena of organic nature, past and present, result from, or are
caused by, the inter-action of those properties of organic matter,
which we have called ATAVISM and VARIABILITY, with the CONDITIONS OF
EXISTENCE; or, in other words,--given the existence of organic matter,
its tendency to transmit its properties, and its tendency occasionally
to vary; and, lastly, given the conditions of existence by which organic
matter is surrounded--that these put together are the causes of the
Present and of the Past conditions of ORGANIC NATURE.
Such is the hypothesis as I understand it. Now let us see how it will
stand the various tests which I laid down just now. In the first
place, do these supposed causes of the phenomena exist in nature? Is
it the fact that in nature these properties of organic matter--atavism
and variability--and those phenomena which we have called the
conditions of existence,--is it true that they exist? Well, of course,
if they do not exist, all that I have told you in the last three or
four lectures must be incorrect, because I have been attempting to prove
that they do exist, and I take it that there is abundant evidence that
they do exist; so far, therefore, the hypothesis does not break down.
But in the next place comes a much more difficult inquiry:--Are the
causes indicated competent to give rise to the phenomena of organic
nature? I suspect that this is indubitable to a certain extent. It is
demonstrable, I think, as I have endeavoured to show you, that they are
perfectly competent to give rise to all the phenomena which are
exhibited by RACES in nature. Furthermore, I believe that they are
quite competent to account for all that we may call purely structural
phenomena which are exhibited by SPECIES in nature. On that point also
I have already enlarged somewhat. Again, I think that the causes
assumed are competent to account for most of the physiological
characteristics of species, and I not only think that they are
competent to account for them, but I think that they account for many
things which otherwise remain wholly unaccountable and inexplicable,
and I may say incomprehensible. For a full exposition of the grounds
on which this conviction is based, I must refer you to Mr. Darwin's
work; all that I can do now is to illustrate what I have said by two or
three cases taken almost at random.
I drew your attention, on a previous evening, to the facts which are
embodied in our systems of Classification, which are the results of the
examination and comparison of the different members of the animal
kingdom one with another. I mentioned that the whole of the animal
kingdom is divisible into five sub-kingdoms; that each of these
sub-kingdoms is again divisible into provinces; that each province may
be divided into classes, and the classes into the successively smaller
groups, orders, families, genera, and species.
Now, in each of these groups, the resemblance in structure among the
members of the group is closer in proportion as the group is smaller.
Thus, a man and a worm are members of the animal kingdom in virtue of
certain apparently slight though really fundamental resemblances which
they present. But a man and a fish are members of the same sub-kingdom
'Vertebrata', because they are much more like one another than either
of them is to a worm, or a snail, or any member of the other
sub-kingdoms. For similar reasons men and horses are arranged as
members of the same Class, 'Mammalia'; men and apes as members of the
same Order, 'Primates'; and if there were any animals more like men
than they were like any of the apes, and yet different from men in
important and constant particulars of their organization, we should
rank them as members of the same Family, or of the same Genus, but as of
distinct Species.
That it is possible to arrange all the varied forms of animals into
groups, having this sort of singular subordination one to the other, is
a very remarkable circumstance; but, as Mr. Darwin remarks, this is a
result which is quite to be expected, if the principles which he lays
down be correct. Take the case of the races which are known to be
produced by the operation of atavism and variability, and the
conditions of existence which check and modify these tendencies. Take
the case of the pigeons that I brought before you; there it was shown
that they might be all classed as belonging to some one of five
principal divisions, and that within these divisions other subordinate
groups might be formed. The members of these groups are related to one
another in just the same way as the genera of a family, and the groups
themselves as the families of an order, or the orders of a class; while
all have the same sort of structural relations with the wild
rock-pigeon, as the members of any great natural group have with a real
or imaginary typical form. Now, we know that all varieties of pigeons
of every kind have arisen by a process of selective breeding from a
common stock, the rock-pigeon; hence, you see, that if all species of
animals have proceeded from some common stock, the general character of
their structural relations, and of our systems of classification, which
express those relations, would be just what we find them to be. In
other words, the hypothetical cause is, so far, competent to produce
effects similar to those of the real cause.
Take, again, another set of very remarkable facts,--the existence of
what are called rudimentary organs, organs for which we can find no
obvious use, in the particular animal economy in which they are found,
and yet which are there.
Such are the splint-like bones in the leg of the horse, which I here
show you, and which correspond with bones which belong to certain toes
and fingers in the human hand and foot. In the horse you see they are
quite rudimentary, and bear neither toes nor fingers; so that the horse
has only one "finger" in his fore-foot and one "toe" in his hind foot.
But it is a very curious thing that the animals closely allied to the
horse show more toes than he; as the rhinoceros, for instance: he has
these extra toes well formed, and anatomical facts show very clearly
that he is very closely related to the horse indeed. So we may say that
animals, in an anatomical sense nearly related to the horse, have those
parts which are rudimentary in him, fully developed.
Again, the sheep and the cow have no cutting-teeth, but only a hard pad
in the upper jaw. That is the common characteristic of ruminants in
general. But the calf has in its upper jaw some rudiments of teeth
which never are developed, and never play the part of teeth at all.
Well, if you go back in time, you find some of the older, now extinct,
allies of the ruminants have well-developed teeth in their upper jaws;
and at the present day the pig (which is in structure closely connected
with ruminants) has well-developed teeth in its upper jaw; so that here
is another instance of organs well-developed and very useful, in one
animal, represented by rudimentary organs, for which we can discover no
purpose whatsoever, in another closely allied animal. The whalebone
whale, again, has horny "whalebone" plates in its mouth, and no teeth;
but the young foetal whale, before it is born, has teeth in its jaws;
they, however, are never used, and they never come to anything. But
other members of the group to which the whale belongs have
well-developed teeth in both jaws.
Upon any hypothesis of special creation, facts of this kind appear to me
to be entirely unaccountable and inexplicable, but they cease to be so
if you accept Mr. Darwin's hypothesis, and see reason for believing
that the whalebone whale and the whale with teeth in its mouth both
sprang from a whale that had teeth, and that the teeth of the foetal
whale are merely remnants--recollections, if we may so say--of the
extinct whale. So in the case of the horse and the rhinoceros: suppose
that both have descended by modification from some earlier form which
had the normal number of toes, and the persistence of the rudimentary
bones which no longer support toes in the horse becomes comprehensible.
In the language that we speak in England, and in the language of the
Greeks, there are identical verbal roots, or elements entering into the
composition of words. That fact remains unintelligible so long as we
suppose English and Greek to be independently created tongues; but when
it is shown that both languages are descended from one original, the
Sanscrit, we give an explanation of that resemblance. In the same way
the existence of identical structural roots, if I may so term them,
entering into the composition of widely different animals, is striking
evidence in favour of the descent of those animals from a common
original.
To turn to another kind of illustration:--If you regard the whole series
of stratified rocks--that enormous thickness of sixty or seventy
thousand feet that I have mentioned before, constituting the only
record we have of a most prodigious lapse of time, that time being, in
all probability, but a fraction of that of which we have no record;--if
you observe in these successive strata of rocks successive groups of
animals arising and dying out, a constant succession, giving you the
same kind of impression, as you travel from one group of strata to
another, as you would have in travelling from one country to
another;--when you find this constant succession of forms, their traces
obliterated except to the man of science,--when you look at this
wonderful history, and ask what it means, it is only a paltering with
words if you are offered the reply,--'They were so created.'
But if, on the other hand, you look on all forms of organized beings as
the results of the gradual modification of a primitive type, the facts
receive a meaning, and you see that these older conditions are the
necessary predecessors of the present. Viewed in this light the facts
of palaeontology receive a meaning--upon any other hypothesis, I am
unable to see, in the slightest degree, what knowledge or signification
we are to draw out of them. Again, note as bearing upon the same
point, the singular likeness which obtains between the successive
Faunae and Florae, whose remains are preserved on the rocks: you never
find any great and enormous difference between the immediately
successive Faunae and Florae, unless you have reason to believe there
has also been a great lapse of time or a great change of conditions.
The animals, for instance, of the newest tertiary rocks, in any part of
the world, are always, and without exception, found to be closely
allied with those which now live in that part of the world. For
example, in Europe, Asia, and Africa, the large mammals are at present
rhinoceroses, hippopotamuses, elephants, lions, tigers, oxen, horses,
etc.; and if you examine the newest tertiary deposits, which contain
the animals and plants which immediately preceded those which now exist
in the same country, you do not find gigantic specimens of ant-eaters
and kangaroos, but you find rhinoceroses, elephants, lions, tigers,
etc.,--of different species to those now living,--but still their close
allies. If you turn to South America, where, at the present day, we
have great sloths and armadilloes and creatures of that kind, what do
you find in the newest tertiaries? You find the great sloth-like
creature, the 'Megatherium', and the great armadillo, the 'Glyptodon',
and so on. And if you go to Australia you find the same law holds
good, namely, that that condition of organic nature which has preceded
the one which now exists, presents differences perhaps of species, and
of genera, but that the great types of organic structure are the same
as those which now flourish.
What meaning has this fact upon any other hypothesis or supposition than
one of successive modification? But if the population of the world, in
any age, is the result of the gradual modification of the forms which
peopled it in the preceding age,--if that has been the case, it is
intelligible enough; because we may expect that the creature that
results from the modification of an elephantine mammal shall be
something like an elephant, and the creature which is produced by the
modification of an armadillo-like mammal shall be like an armadillo.
Upon that supposition, I say, the facts are intelligible; upon any
other, that I am aware of, they are not.
So far, the facts of palaeontology are consistent with almost any form
of the doctrine of progressive modification; they would not be
absolutely inconsistent with the wild speculations of De Maillet, or
with the less objectionable hypothesis of Lamarck. But Mr. Darwin's
views have one peculiar merit; and that is, that they are perfectly
consistent with an array of facts which are utterly inconsistent with
and fatal to, any other hypothesis of progressive modification which
has yet been advanced. It is one remarkable peculiarity of Mr.
Darwin's hypothesis that it involves no necessary progression or
incessant modification, and that it is perfectly consistent with the
persistence for any length of time of a given primitive stock,
contemporaneously with its modifications. To return to the case of the
domestic breeds of pigeons, for example; you have the Dove-cot pigeon,
which closely resembles the Rock pigeon, from which they all started,
existing at the same time with the others. And if species are
developed in the same way in nature, a primitive stock and its
modifications may, occasionally, all find the conditions fitted for
their existence; and though they come into competition, to a certain
extent, with one another, the derivative species may not necessarily
extirpate the primitive one, or 'vice versa'.
Now palaeontology shows us many facts which are perfectly harmonious
with these observed effects of the process by which Mr. Darwin supposes
species to have originated, but which appear to me to be totally
inconsistent with any other hypothesis which has been proposed. There
are some groups of animals and plants, in the fossil world, which have
been said to belong to "persistent types," because they have persisted,
with very little change indeed, through a very great range of time,
while everything about them has changed largely. There are families of
fishes whose type of construction has persisted all the way from the
carboniferous rock right up to the cretaceous; and others which have
lasted through almost the whole range of the secondary rocks, and from
the lias to the older tertiaries. It is something stupendous this--to
consider a genus lasting without essential modifications through all
this enormous lapse of time while almost everything else was changed
and modified.
Thus I have no doubt that Mr. Darwin's hypothesis will be found
competent to explain the majority of the phenomena exhibited by species
in nature; but in an earlier lecture I spoke cautiously with respect to
its power of explaining all the physiological peculiarities of species.
There is, in fact, one set of these peculiarities which the theory of
selective modification, as it stands at present, is not wholly
competent to explain, and that is the group of phenomena which I
mentioned to you under the name of Hybridism, and which I explained to
consist in the sterility of the offspring of certain species when
crossed one with another. It matters not one whit whether this
sterility is universal, or whether it exists only in a single case.
Every hypothesis is bound to explain, or, at any rate, not be
inconsistent with, the whole of the facts which it professes to account
for; and if there is a single one of these facts which can be shown to
be inconsistent with (I do not merely mean inexplicable by, but contrary
to) the hypothesis, the hypothesis falls to the ground,--it is worth
nothing. One fact with which it is positively inconsistent is worth as
much, and as powerful in negativing the hypothesis, as five hundred. If
I am right in thus defining the obligations of an hypothesis, Mr.
Darwin, in order to place his views beyond the reach of all possible
assault, ought to be able to demonstrate the possibility of developing
from a particular stock by selective breeding, two forms, which should
either be unable to cross one with another, or whose cross-bred
offspring should be infertile with one another.
For, you see, if you have not done that you have not strictly fulfilled
all the conditions of the problem; you have not shown that you can
produce, by the cause assumed, all the phenomena which you have in
nature. Here are the phenomena of Hybridism staring you in the face,
and you cannot say, 'I can, by selective modification, produce these
same results.' Now, it is admitted on all hands that, at present, so
far as experiments have gone, it has not been found possible to produce
this complete physiological divergence by selective breeding. I stated
this very clearly before, and I now refer to the point, because, if it
could be proved, not only that this 'has' not been done, but that it
'cannot' be done; if it could be demonstrated that it is impossible to
breed selectively, from any stock, a form which shall not breed with
another, produced from the same stock; and if we were shown that this
must be the necessary and inevitable results of all experiments, I hold
that Mr. Darwin's hypothesis would be utterly shattered.