"I imagine that most of my contemporaries who thought seriously about the matter were very much in my own state of mind—inclined to say to Mosaists and Evolutionists, 'a plague on both your houses!' and disposed to turn aside from an interminable and apparently fruitless discussion to labour in the fertile fields of ascertainable fact. And I may, therefore, further suppose that the publication of the Darwin and Wallace papers in 1858, and still more that of the Origin in 1859, had the effect upon them of that of a flash of light which, to a man who has lost himself in a dark night, suddenly reveals a road which, whether it takes him straight home or not, certainly goes his way. That which we were looking for and could not find, was a hypothesis respecting the origin of known organic forms, which assumed the operation of no causes but such as could be proved to be actually at work. We wanted, not to pin our faith to that or any other speculation, but to get hold of clear and definite conceptions which could be brought face to face with facts and have their validity tested. The Origin provided us with the working hypothesis we sought. Moreover, it did us the immense service of freeing us for ever from the dilemma—refuse to accept the creation hypothesis, and what have you to propose that can be accepted by any cautious reasoner? In 1857 I had no answer ready, and I do not think that anyone else had. A year later, we reproached ourselves with dulness for being perplexed by such an enquiry. My reflection, when I first made myself master of the central idea of the Origin was, 'how exceedingly stupid not to have thought of that.' I suppose that Columbus's companions said much the same when he made the egg to stand on end. The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness, and the beacon-fire of the Origin guided the benighted.
"Whether the particular shape which the doctrine of evolution, as applied to the organic world, took in Darwin's hands, would prove to be final or not, was, to me, a matter of indifference. In my earliest criticisms of the Origin I ventured to point out that its logical foundation was insecure so long as experiments in selective breeding had not produced varieties which were more or less infertile; and that insecurity remains up to the present time. But, with any and every critical doubt which my sceptical ingenuity could suggest, the Darwinian hypothesis remained incomparably more probable than the creation hypothesis. And if we had none of us been able to discern the paramount significance of some of the most patent and notorious of natural facts, until they were, so to speak, thrust under our noses, what force remained in the dilemma—creation or nothing? It was obvious that, hereafter, the probability would be immensely greater that the links of natural causation were hidden from our purblind eyes, than that natural causation should be unable to produce all the phenomena of nature. The only rational course for those who had no other object than the attainment of truth, was to accept 'Darwinism' as a working hypothesis, and see what could be made of it. Either it would prove its capacity to elucidate the fact of organic life, or it would break down under the strain. This was surely the dictate of common sense, and for once common-sense carried the day. The result has been that complete volte-face of the whole scientific world which must seem so surprising to the present generation. I do not mean to say that all the leaders of biological science have avowed themselves Darwinians; but I do not think that there is a single zoölogist, or botanist, or palæontologist, among the multitude of active workers of this generation, who is other than an evolutionist profoundly influenced by Darwin's views. Whatever may be the ultimate fate of the particular theory put forth by Darwin, I venture to affirm that, so far as my knowledge goes, all the ingenuity and all the learning of hostile critics has not enabled them to adduce a solitary fact of which it can be said that it is irreconcilable with the Darwinian theory. In the prodigious variety and complexity of organic nature, there are multitudes of phenomena which are not deducible from any generalisation we have yet reached. But the same may be said of every other class of natural objects. I believe that astronomers cannot yet get the moon's motions into perfect accordance with the theory of gravitation."
These quotations make plain the historical fact that Huxley was convinced of evolution because Darwin, by his theory of natural selection, brought forward an actual cause that could be seen in operation, and that was competent to produce new species. As soon as the "flash of light" came, it revealed to Huxley the vast store of evidence that he had unconsciously accumulated, and it set him at once to work collecting more evidence. If we bear in mind the distinction between evolution and natural selection, the well-known subsequent history of the relations between Huxley and what was known popularly as Darwinism becomes clear and intelligible. From first to last he accepted evolution; from first to last he accepted natural selection as by far the most reasonable hypothesis that had been brought forward, and as infinitely more in accordance with the observed facts of nature than any theory of the immediate action of supernatural creative power. As time went on, and the influence of Darwin's theory made evolution acceptable to a wider and wider range of people, until it passed into the common knowledge of the world, that confusion of which we have spoken arose between evolution and Darwin's particular theory. And as knowledge grew, and the number of biologists increased in the striking fashion of this last half-century, while the evidence for evolution continued to increase with an unexpected rapidity, every detail of the purely Darwinian theory became more and more subjected to rigid scrutiny. Most educated people, unless their education has been largely in an experimental science, find difficulty in understanding the relation in the minds of naturalists between "authority" and "knowledge." We do not know, for instance, that the structure of the Medusæ consists essentially of two foundation-membranes, because Huxley, one of the greatest authorities in anatomy that the world has seen, told us that it was so. We know it because, Huxley having told us that it was so, we are able at any time with a microscope and dissecting needles to observe the fact for ourselves. It is true, that unless we are making a special study of the Medusæ we do not repeat the observation in the case of so many different forms of Medusæ as Huxley studied; but it is partof our training to observe for ourselves in a sufficient number of cases to test the correspondence between statement and fact before we accept the generalisation of any authority. And we learn, or at least have the opportunity of learning, in the whole habit of our lives as naturalists, to distinguish carefully between knowledge of which personal observation is an essential part, and opinion or belief which may or may not be based upon authority, but which in any case is devoid of the corroboration of personal observation. When a piece of new anatomical or physiological work is published in a technical journal, it is read by a large number of anatomists and physiologists, and if the work is apparently of an important kind, bearing on the general problems that even specialists have to follow, they all at once set to work in their laboratories to make corroborative dissections or experiments, and it is part of every modern account of a biological discovery to tell exactly the methods by which results were got, in order that this process of corroboration may be set about easily. The question as to whether or no natural selection were the sole or chief cause, or indeed a cause at all, of evolution is not yet, and perhaps never will be, a matter of knowledge in the scientific sense. At the most, we can see for ourselves only that selection does bring about changes at least as great as the differences between natural species. The evidence for this we have before our eyes, if we choose to see, on a stock farm; in the breeding yards of any keeper of "fancy" animals; or in the nursery gardens of any florist. So far, Huxley accepted the Darwinian principle as a definite contribution to knowledge; and so far the whole body of biologists has followed him. Beyond this the truth of the Darwinian principle is a matter of inference or judgment; of balancing probabilities and improbabilities. In multitude of counsellors there is said to be wisdom, and what we learn from the counsellors of biology all over the world is that some maintain that natural selection is the only probable agency in effecting evolution, and that it is competent to account for all the changes which we know to have taken place; others hold that its probable influence has been over-rated; and others, again, think that it has been one of the many causes that have brought about the kaleidoscopic variety of organic nature. Huxley remained to the last among those who distinguished in the clearest way between natural selection as an exceedingly ingenious and probable hypothesis, and a proved cause; and he was always careful, especially when he was writing for or speaking in the presence of those who like himself accepted the fact of evolution as proven, to distinguish between this provisional hypothesis as to how evolution had come about, and definite knowledge that it had come about in this way. Two passages from Huxley's writings, one written in 1860 in the Westminster Review, and the second written in 1893, in the preface to the volume of his collected essays which contained a reprint of the Westminster article, will make plain the continuity of Huxley's attitude:
"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 assuredly with 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 natural or artificial. 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 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 the 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 or overlooked."—(Westminster Review, 1860.)
"We should leave a very wrong impression on the reader's mind if we permitted him to suppose that the value of Darwin's 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."—(Ibid.)
"Those who take the trouble to read the essays published in 1859 and 1860, will, I think, do me the justice to admit that my zeal to secure fair play for Mr. Darwin did not drive me into the position of a mere advocate; and that, while doing justice to the greatness of the argument, I did not fail to indicate its weak points. I have never seen any reason for departing from the position which I took up in these two essays; and the assertion which I sometimes meet with nowadays that I have 'recanted' or changed my opinions about Mr. Darwin's views is quite unintelligible to me.
"As I have said in the seventh essay, the fact of evolution is to my mind sufficiently evidenced by palæontology; and I remain of the opinion expressed in the second, that until selective breeding is definitely proved to give rise to varieties infertile with one another, the logical foundation of the theory of natural selection is quite incomplete. We still remain very much in the dark about the causes of variation; the apparent inheritance of acquired characters in some cases; and the struggle for existence within the organism, which probably lies at the bottom of both these phenomena."—(1893, Preface.)
Finally, when he was awarded the Darwin Medal of the Royal Society, on November 30, 1894, in the course of an address at the anniversary dinner of the Society, he said, as reported in the Times next day: