The Origin of Species
by Thomas H. Huxley
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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
this hypothesis is of three kinds. First, he endeavors 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 endeavored 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 endeavors 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 is
inconsistent with the origin of species in this way? If these questions
can be answered in the affirmative, Mr. Darwin's view steps out of the
rank of hypotheses into those of proved theories; but, so long as the
evidence at present adduced falls short of enforcing that affirmation, so
long, to our minds, must the new doctrine be content to remain among the
former—an extremely valuable, and in the highest degree probable,
doctrine, indeed the only extant hypothesis which is worth anything in a
scientific point of view; but still a hypothesis, and not yet the theory
of species.
After much consideration, and with assuredly no bias
against Mr. Darwin's views, it is our clear conviction that, as the
evidence stands, it is not absolutely proven that a group of animals,
having all the characters exhibited by species in Nature, has ever been
originated by selection, whether artificial or natural. Groups having the
morphological character of species—distinct and permanent races in
fact—have been so produced over and over again; but there is no
positive evidence, at present, that any group of animals has, by variation
and selective breeding, given rise to another group which was, even in the
least degree, infertile with the first. Mr. Darwin is perfectly aware of
this weak point, and brings forward a multitude of ingenious and important
arguments to diminish the force of the objection. We admit the value of
these arguments to their fullest extent; nay, we will go so far as to
express our belief that experiments, conducted by a skillful physiologist,
would very probably obtain the desired production of mutually more or less
infertile breeds from a common stock, in a comparatively few years; but
still, as the case stands at present, this "little rift within the lute" is
not to be disguised nor overlooked.
In the remainder of Mr. Darwin's argument our own private
ingenuity has not hitherto enabled us to pick holes of any great importance;
and judging by what we hear and read, other adventurers in the same field do
not seem to have been much more fortunate. It has been urged, for instance,
that in his chapters on the struggle for existence and on natural selection,
Mr. Darwin does not so much prove that natural selection does occur, as that
it must occur; but, in fact, no other sort of demonstration is attainable.
A race does not attract our attention in Nature until it has, in all
probability, existed for a considerable time, and then it is too late to
inquire into the conditions of its origin. Again, it is said that there is
no real analogy between the selection which takes place under domestication,
by human influence, and any operation which can be effected by Nature, for
man interferes intelligently. Reduced to its elements, this argument implies
that an effect produced with trouble by an intelligent agent must, à
fortiori, be more troublesome, if not impossible, to an unintelligent
agent. Even putting aside the question whether Nature, acting as she does
according to definite and invariable laws, can be rightly called an
unintelligent agent, such a position as this is wholly untenable. Mix salt
and sand, and it shall puzzle the wisest of men, with his mere natural
appliances, to separate all the grains of sand from all the grains of salt;
but a shower of rain will effect the same object in ten minutes. And so,
while man may find it tax all his intelligence to separate any variety
which arises, and to breed selectively from it, the destructive agencies
incessantly at work in Nature, if they find one variety to be more soluble
in circumstances than the other, will inevitably, in the long run,
eliminate it.
A frequent and a just objection to the Lamarckian
hypothesis of the transmutation of species is based upon the absence of
transitional forms between many species. But against the Darwinian
hypothesis this argument has no force. Indeed, one of the most valuable
and suggestive parts of Mr. Darwin's work is that in which he proves, that
the frequent absence of transitions is a necessary consequence of his
doctrine, and that the stock whence two or more species have sprung, need
in no respect be intermediate between these species. If any two species
have arisen from a common stock in the same way as the carrier and the
pouter, say, have arisen from the rock-pigeon, then the common stock of
these two species need be no more intermediate between the two than the
rock-pigeon is between the carrier and pouter. Clearly appreciate the
force of this analogy, and all the arguments against the origin of
species by selection, based on the absence of transitional forms, fall
to the ground. And Mr. Darwin's position might, we think, have been even
stronger than it is if he had not embarrassed himself with the aphorism,
"Natura non facit saltum," which turns up so often in his pages.
We believe, as we have said above, that Nature does make jumps now and
then, and a recognition of the fact is of no small importance in
disposing of many minor objections to the doctrine of transmutation.
But we must pause. The discussion of Mr. Darwin's
arguments in detail would lead us far beyond the limits within which we
proposed, at starting, to confine this article. Our object has been
attained if we have given an intelligible, however brief, account of the
established facts connected with species, and of the relation of the
explanation of those facts offered by Mr. Darwin to the theoretical
views held by his predecessors and his contemporaries, and, above all,
to the requirements of scientific logic. We have ventured to point out
that it does not, as yet, satisfy all those experiments; 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 tomorrow, 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.
[ Thomas H. Huxley, "The Origin of Species," from
Collected Essays, vol. 2, Darwiniana, London: Macmillan,
1860, pp. 71-79; Reprinted in Michael Ruse,
But is it
Science, Amherst, NY: Prometheus Books, 1996, pp. 106-109. ]
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