Thomas Henry Huxley; A Sketch Of His Life And Work Part 4

Huxley then proceeded to shew that uniformitarianism and catastrophism had neglected this last and most important branch of geology, the attempt to trace the interaction of causes which had brought the world into its present condition. He gave a striking display of the wide knowledge of his reading by going back to the foundation of this branch of modern science, and giving a masterly account of the then little-known treatise of Immanuel Kant, who in 1775 had written _An Attempt to Account for the Const.i.tutional and Mechanical Origin of the Universe upon Newtonian Principles_. Next he declared that evolution embraced all that was sound in both catastrophism and uniformitarianism while rejecting the arbitrary limits and a.s.sumptions of both.

Finally he came to the great question to which these observations upon the existing schools of geology had led. The most distinguished physicist of the age, then Sir William Thomson, now Lord Kelvin, and Huxley's immediate successor in the Presidential Chair of the Royal Society, had stated that the English school of geology had a.s.sumed an impossible age for the earth. By physical reasonings, Thomson stated that he was able to prove "That the existing state of things on the earth--all geological history showing continuity of life--must be limited within some such period of time as one hundred million years."

This p.r.o.nouncement had been received with acclamation by those who feared the geological and biological sciences, as a sign of internal dissensions within the house of science. Huxley, then, as all through the latter part of his life, at once const.i.tuted himself the champion of science, and, taking Thomson's arguments one by one, shewed by a series of masterly deductions from known facts that there was a great deal to be said for the other side, and that physicists were as little certain as geologists could be of the exact duration of time that had elapsed since the dawn of life. His plea for more time since the cooling of the globe than physicists were willing to allow remains one of the cla.s.sics of geological literature. But he carried the question much farther. The inference which was widely drawn by the enemies of evolution from the arguments of Sir William Thomson was that if geologists had overestimated the age of the cooled earth there was not time for the evolution of animals and plants to have taken place.

Huxley pointed out a fact which should be quite obvious, but which even yet is frequently neglected. The evidence for the gradual appearance of life in the past history of the earth depends simply on the fact that the successive forms of life appear in successive strata, and the length of time taken for these changes simply depends upon the length of time which was taken up by the formation of the strata. Our only reason for supposing the evolution of life, made plain by fossil records, to have taken place very slowly is that geologists have stated that the deposition of the strata took place very slowly. Whether these strata were deposited slowly or less slowly, we know that the forms of life changed at the same rate.

"Biology takes her time from geology. The only reason we have for believing in the slow rate of change in living forms is the fact that they persist through a series of deposits which, geology informs us, have taken a long while to make. If the geological clock is wrong, all the naturalist will have to do is to modify his notion of the rapidity of change accordingly; and I venture to point out that, when we are told that the limitation of the period during which living beings have inhabited this planet to one, two, or three hundred million years requires a complete revolution in geological speculation, the _onus probandi_ rests on the maker of the a.s.sertion, who brings forward not a shadow of evidence in its support."

Perhaps, although this is now an old controversy, it is worth while to recall that the keenness of Huxley's language was not directed against Sir William Thomson, between whom and Huxley there was no more than the desire to argue out an interesting scientific question upon which their conclusions differed, but between Huxley and those outsiders who were always ready to turn any dubious question in science into an argument discrediting the general conclusions of science.

The last time that Huxley occupied the Presidential Chair of the Geological Society was in 1870, and he occupied his Presidential address by a review of the "old judgments" which he had given in the course of his first address in 1862. The address was ent.i.tled "Palaeontology and Evolution," and the most important part of it was a complete withdrawal of the fears he had expressed that geology would not supply definite evidence of the transformation of species.

Important discoveries had come thick and fast; and, at least in the case of the higher vertebrates, he declared that, however one might "sift and criticise them," they left a clear balance in favour of the doctrine of the evolution of living forms one from another. But, with his usual critical spirit, examining arguments that bore against a conclusion for which he hoped almost more stringently than arguments apparently favourable to what he expected to be true, Huxley made an important distinction, the value of which becomes more and more apparent as time goes on. In the first flush of enthusiasm for Darwinism, zoologists and palaeontologists allowed their zeal to outrun discretion in the formation of family trees. They examined large series of living or extinct creatures, and so soon as they found gradations of structure present, they arranged their specimens in a linear series, from the simplest to the most complex, and declared that the arrangement was a representation of the family tree. The fact that the line of descent apparently could have followed along the direction they suggested they were inclined to take as evidence that it had so followed. Huxley made the most careful distinction between what he called intermediate types and types with a right to be placed in linear order,

Every fossil which takes an intermediate place between forms of life already known may be said, so far as it is intermediate, to be evidence in favour of evolution, inasmuch as it shews a possible road by which evolution may have taken place. But the mere discovery of such a form does not, in itself, prove that evolution took place by and through it, nor does it const.i.tute more than a presumptive evidence in favour of evolution in general. The fact that _Anoplotheridae_ are intermediate between pigs and ruminants does not tell us whether the ruminants have come from the pigs or the pigs from the ruminants, or both from _Anoplotheridae_, or whether pigs, ruminants, and _Anoplotheridae_; alike may not have diverged from some common stock.

A familiar instance will make the point at issue plain. Everyone knows that in many respects, in the structure of the skeleton, and the curve of the backbone, and in the development of the brain, the man-like monkeys, the gorilla and its allies, are intermediate between man and the lower monkeys. In the early days of evolution it was a.s.sumed frequently that the gorilla, etc., were therefore to be regarded as ancestors of man, and they appear as such in more than one well-known treatise on evolutionary biology. We now know that it is exceedingly probable that the gorilla and its allies, although truly intermediate types, and truly shewing a possible path of evolution from the brute to man, are not the actual ancestors of man, but cousins, descendants like man from some more or less remote common ancestor. And the tendency of recent advances in knowledge is more and more to throw stress on the value of Huxley's distinction, and to minimise confusion between "intermediate" and truly ancestral types.

CHAPTER VI

HUXLEY AND DARWIN

Early Ideas on Evolution--Erasmus Darwin--Lamarck--Herbert Spencer--Difference between Evolution and Natural Selection--Huxley's Preparation for Evolution--The Novelty of Natural Selection--The Advantage of Natural Selection as a Working Hypothesis--Huxley's Unchanged Position with regard to Evolution and Natural Selection from 1860 to 1894.

From our attempt to place together as much as possible of Huxley's geological work in the last chapter, it followed that we antic.i.p.ated much that falls properly within this chapter. The year 1859, the date of publication of _The Origin of Species_, is a momentous date in the history of this century, as it was the year in which there was given to the world a theory that not only revolutionised scientific opinion, but altered the trend of almost every branch of thought. To understand this great change, and the part played in it by Huxley, it is necessary to be quite clear as to what Darwin did. In the first place, he did not invent evolution. The idea that all the varied structures in the world, the divergent forms of rocks and minerals and crystals, the innumerable trees and herbs that cover the face of the earth like a mantle, and all the animal host of creatures great and small that dwell on the land or dart through the air or people the waters,--that all these had arisen by natural laws from a primitive unformed material was known to the Greeks, was developed by the Romans, and even received the approval of early Christian Fathers, who wrote long before the idea had been invented that the naive legends of the Old Testament were an authoritative and literal account of the origin of the world. After a long interval, in which scientific thought was stifled by theological dogmatism, the theory of evolution, particularly in its application to animals, began to reappear, long before Darwin published _The Origin of Species_. Buffon, the great French naturalist, and Erasmus Darwin, the grandfather of Charles, had expressed in the clearest way the possibility that species had not been created independently, but had arisen from other species. Lamarck had worked out a theory of descent in the fullest detail, and regarded it as the foundation of the whole science of biology. He taught that the beginning of life consisted only of the simplest and lowest plants and animals; that the more complex animals and plants arose from these, and that even man himself had come from ape-like mammals. He held that the course of development of the earth and of all the creatures upon it was a slow and continuous change, uninterrupted by violent revolutions. He summed up the causes of organic evolution in the following propositions[D]:

"1. Life tends by its inherent forces to increase the volume of each living body and of all its parts up to a limit determined by its own needs.

"2. New wants in animals give rise to new movements which produce organs.

"3. The development of these organs is in proportion to their employment.

"4. New developments are transmitted to offspring."

He supported especially the last two propositions by a series of examples as to the effects of use and disuse; and the most famous of these, the theory that giraffes had produced their long necks by continually stretching up towards the trees on which they fed, is well known to everyone. However, the ingenious speculations of Lamarck were unsupported by a sufficient range of actual knowledge of anatomy, and lacked experimental proof. He entirely failed to convince his contemporaries; and Darwin himself, in a letter to Lyell, declared that he had gained nothing from two readings of Lamarck's book. There can be little doubt but that several Continental writers, in particular Haeckel, have exaggerated Lamarck's services to the development of the idea of evolution. On the other hand, Lyell, although he strongly opposed the ideas of Lamarck and some curious notions of progressional creation due to the great Aga.s.siz, had prepared the way for Darwin by his advocacy of natural causes and slow changes in opposition to the catastrophic and miraculous views in vogue. Above all, Herbert Spencer had argued most strenuously in favour of evolution. Thus, in an important pa.s.sage quoted by Mr. Clodd from the _Leader_ of March 20, 1852, Spencer had written as follows:

"Those who cavalierly reject the theory of evolution, as not adequately supported by facts, seem quite to forget that their own theory is not supported by facts at all. Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but a.s.sume that their own needs none. Here we find, scattered over the globe, vegetable and animal organisms numbering, of the one kind (according to Humboldt) some 320,000 species, and of the other, some 2,000,000 species (see Carpenter); and if to these we add the numbers of animal and vegetable species that have become extinct, we may safely estimate the number of species that have existed, and are existing, on the earth, at no less than ten millions. Well, which is the most rational theory about these ten millions of species?

Is it most likely that there have been ten millions of special creations; or is it most likely that by continual modifications, due to change of circ.u.mstances, ten millions of varieties have been produced, as varieties are being produced still?... Even could the supporters of the development hypothesis merely shew that the origination of species by the process of modification is conceivable, they would be in a better position than their opponents. But they can do much more than this. They can shew that the process of modification has effected, and is effecting, decided changes in all organisms subject to modifying influences.... They can shew that in successive generations these changes continue, until ultimately the new conditions become the natural ones. They can shew that in cultivated plants, domesticated animals, and in the several races of men, such alterations have taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species have been founded. They can shew, too, that the changes daily taking place in ourselves--the facility that attends long practice, and the loss of apt.i.tude that begins when practice ceases,--the strengthening of the pa.s.sions habitually gratified, and the weakening of those habitually curbed,--the development of every faculty, bodily, moral, intellectual, according to the use made of it--are all explicable on this principle. And thus they can shew that throughout all organic nature there is at work a modifying influence of the kind they a.s.sign as the cause of these specific differences; an influence which, though slow in its action, does, in time, if the circ.u.mstances demand it, produce marked changes--an influence which, to all appearance, would produce in the millions of years, and under the great varieties of condition which geological records imply, any amount of change."

These and many other instances which might be brought together from the published writings of the half-century before the publication of the _Origin_, show conclusively that the idea of evolution was far from new, and that all through the first part of this century dissatisfaction with the doctrine of the fixity of species and of their miraculous creation was growing. The great contribution of Darwin was this: First, by his theory of natural selection, he brought together the known facts of variation, of struggle for existence, and of adaptation to varying conditions, in such a way that they provided men with a rational and known cause, a cause the operation of which could be seen, for the origin of species by means of preservation of favoured races. Next, as to the origin of species, he brought together not only proofs of the actual operation of natural selection, but a body of evidence in favour of the fact of evolution that was, beyond all comparison, more striking than had been adduced by any earlier philosophical or biological writer. He convinced naturalists that evolution was by far the most probable way in which the living world had come to be what it is, and he made them turn to examination of the animal and vegetable kingdoms with a lively hope that the past history of the living world was not an insoluble problem. Darwin's doctrine brought a new life into biological study, and the result of the incomparably greater bulk of investigation that followed the year 1859 was a continual increase of evidence in favour of the probability of evolution, until now the whole scientific world, and the majority of those who are unscientific, are content to accept evolution as the only reasonable explanation of the living world. It is well to remember that while Darwin, by bringing forward the theory of struggle for existence and resulting survival of the fittest, was the actual cause of the present a.s.sured position of evolution as a first principle of science, it by no means follows that the survival of the fittest has become similarly a first principle of science. At cross roads a traveller may choose the right path from a quite unsatisfactory reason. Darwin himself, in the act of bringing forward his own theory of natural selection, admitted the possibility of the co-operation of many other agencies in evolution, and at various times during the course of his life he was inclined to attach, now more now less, importance to these additional agencies. Huxley, as we shall soon come to see, never wavered in his adhesion to the facts of evolution after 1859; but, from first to last, regarded natural selection as only the most probable cause of the occurrence of evolution. Other naturalists, of whom the best-known are Weismann in Germany, Ray Lankester in England, and W.K. Brooks in America, have come to attach a continually increasing importance to the purely Darwinian factor of natural selection; while others again, such as Herbert Spencer in England, and the late Professor Cope and a large American school, have advocated more and more strongly the importance of what may be called the Lamarckian factors of evolution,--the inherited effects of increased or diminished use of organs, the direct influence of the environment, and so forth. From the fact that Darwin has persuaded the world of the truth of evolution, evolution is often called Darwinism; and in this historically just though scientifically inaccurate sense of the term, Huxley was a strict Darwinian, a Darwinian of the Darwinians. From the facts that, although natural selection had been formulated by several writers before Darwin, and had been simultaneously elaborated by Wallace and Darwin, the _Origin of Species_ was the foundation of the modern acceptation of evolution, and natural selection was the key-note of the origin of species, natural selection may be called Darwinism with both historical and scientific accuracy; and in this sense of the term Huxley was a Darwinian; a convinced but free-thinking and broad-minded Darwinian, who was far from persuaded that his tenet had a monopoly of truth, and who delighted in shewing the distinctions between what seemed to him probable and what was proved, and in absorbing from other doctrines whatever he thought worthy to be absorbed. The present writer has thought it so important to distinguish between these two sides of the word _Darwinism_, that for the sake of clearness he has stated what he believes to be the truth of Huxley's relation to Darwin before beginning detailed exposition of it.

In consideration of Huxley's position before 1859, the most interesting feature of his zoological work is the gradual preparation that it was making in his mind for the doctrine of the _Origin_. He was like an engineer boring a tunnel through a mountain, but ignorant of how near he was to the pleasant valley on the other side; and, above all, ignorant how rapidly he was being met by a much more mighty excavation from the other side. To use what is perhaps a more exact simile: he was like a child with half the pieces of a puzzle-map, slowly linking them together as far as they would fit, and quite ignorant that presently the remaining half would suddenly be given him, and with almost no trouble would at once fit into the gaps he had necessarily left, and transform a meaningless pattern into a perfect and intelligible whole. Let us consider some of these map pieces. The ultimate picture was the conception of the whole world of life, past and present, as a single family tree growing up from the simplest possible roots, and gradually spreading out first into the two main branches of animals and plants, and then into the endless series of complicated ramifications that make up living and extinct animals and plants. Huxley was piecing together the scattered fragments, and gradually learning to see here and there whole branches, as yet separate at their lower ends, but in themselves shapely, and showing a general resemblance to one another in the gradual progression from simple to complex. The greatest of these branches that he had pieced together was the group of Medusae and their allies, now known as Clenterates. He had formed similar branches for the Molluscs and minor branches for the Salps and Ascidians, and, in his general lectures on the whole animal kingdom, he had shadowed out the broad arrangement of the main divisions, or, as he called them, _types_. He had seen in each particular branch the clearest evidence of the laws of growth which had directed its development, and had realised that these laws of growth, consisting of gradual modifications of common typical structures, were identical in the different branches. He had taken clear hold of Von Baer's conception that the younger stages of different types were more alike than the adult stages, and here and there he had made comparisons between the younger stages or simplest forms of his different branches, and had shown that, without completely realising it, he was ready for the idea that just as the separate pieces could be arranged to form orderly branches, so the separate branches might come to be arranged as a single tree. And finally, in his lectures on "Protoplasm and Cells," and on the "Common Structure of the Animal and Plant Kingdoms," he had reached the conclusion that the two main divisions of the living world were formed of the same stuff, displayed in identical fashion the elementary functions of life, and were creatures of the same order.

But, notwithstanding this close approach to modern conceptions, he was not an evolutionist. When, in public, he expressed deliberate convictions, these convictions were against the general idea of evolution, until very shortly before 1859. In this opposition he was supported partly by the critical scepticism of his mind, which in all things made him singularly unwilling to accept any theories of any kind, but chiefly from the fact that the books of the two chief supporters of evolutionary conceptions impressed him very unfavourably. Huxley writes:

"I had studied Lamarck attentively, and I had read the _Vestiges_ with due care; but neither of them afforded me any good ground for changing my negative and critical att.i.tude. As for the _Vestiges_, I confess that the book simply irritated me by the prodigious ignorance and thoroughly unscientific habit of mind manifested by the writer. If it had any influence on me at all, it set me against evolution; and the only review I ever have qualms of conscience about, on the ground of needless savagery is one I wrote on the _Vestiges_ while under that influence. With respect to the _Philosophie Zoologique_, it is no reproach to Lamarck to say that the discussion of the species question in that work, whatever might be said for it in 1809, was miserably below the level of the knowledge of half a century later. In that interval of time, the elucidation of the structure of the lower animals and plants had given rise to wholly new conceptions of their relations; histology and embryology, in the modern sense, had been created; physiology had been reconst.i.tuted; the facts of distribution, geological and geographical, had been prodigiously multiplied and reduced to order. To any biologist whose studies had carried him beyond mere species-mongering, in 1850 one-half of Lamarck's arguments were obsolete, and the other half erroneous or defective, in virtue of omitting to deal with the various cla.s.ses of evidence which had been brought to light since his time. Moreover his one suggestion as to the cause of the gradual modification of species--effort excited by change of conditions--was, on the face of it, inapplicable to the whole vegetable world. I do not think that any impartial judge who reads the _Philosophie Zoologique_ now, and who afterwards takes up Lyell's trenchant and effective criticism (published as far back as 1830) will be disposed to allot to Lamarck a much higher place in the establishment of biological evolution than that which Bacon a.s.signs to himself in relation to physical science generally--_buccinator tantum_".

On the other hand, Huxley's friendship with Darwin and with Lyell began to make him less certain about the fixity of species. He tells us that during his first interview with Darwin, which occurred soon after his return from the _Rattlesnake_, he

"expressed his belief in the sharpness of the lines of demarcation between natural groups and in the absence of transitional forms, with all the confidence of youth and imperfect knowledge. I was not aware at that time that he had been many years brooding over the species question; and the humorous smile which accompanied his gentle answer, that such was not altogether his view, long haunted and puzzled me."

An elaborate study of Lyell's works helped largely in destroying this youthful confidence, and a letter written by Lyell and quoted by Huxley in the chapter he communicated to Darwin's _Life and Letters_, states that in April, 1856, "when Huxley, Hooker, and Wollaston were at Darwin's last week they (all four of them) ran a tilt against species; further I believe, than they are prepared to go." Another quotation from Huxley's essay on _The Reception of the Origin of Species_ will make it plain beyond all doubt that he was not a Darwinian before Darwin.

[Ill.u.s.tration: SIR JOSEPH DALTON HOOKER]

"Thus, looking hack into the past, it seems to me that my own position of critical expectancy was just and reasonable, and must have been taken up, on the same grounds, by many other persons.

If Aga.s.siz had told me that the forms of life which had successively tenanted the globe were the incarnations of successive thoughts of the Deity; and that He had wiped out one set of these embodiments by an appalling geological catastrophe as soon as His ideas took a more advanced shape, I found myself not only unable to admit the accuracy of the deductions from the facts of palaeontology, upon which this astounding hypothesis was founded, but I had to confess my want of means of testing the correctness of his explanation of them. And besides that, I could by no means see what the explanation explained. Neither did it help me to be told by an eminent anatomist that species had succeeded one another in time, in virtue of a 'continuously operative creational law'. That seemed to me to be no more than saying that species had succeeded one another in the form of a vote-catching resolution, with 'law' to please the man of science and 'creational' to draw the orthodox. So I took refuge in that _thatige Skepsis_ which Goethe has so well defined; and, reversing the apostolic precept to be all things to all men, I usually defended the tenability of the received doctrines when I had to do with the trans.m.u.tationists, and stood up for the possibility of trans.m.u.tation among the orthodox--thereby, no doubt, increasing an already current, but quite undeserved, reputation for needless combativeness."

What transformed Huxley's views and the views of his contemporaries who accepted Darwinism was not so much the evidence in favour of evolution contained in the _Origin_, as the illuminating doctrine of natural selection which for the first time supplied naturalists with a reasonable explanation of how evolution might have come about, both in the animal and vegetable kingdoms. As soon as this reason was provided them, they turned to the store of facts within their own knowledge, and rapidly arranged the evidence which had been lurking only partly visible in favour of the fact of evolution. It cannot be disputed that here and there earlier writers than Darwin and Wallace had suggested the possibility of natural selection acting upon existing variations so as to cause survival of the fittest.

MacGillivray, the Scots naturalist, and the father of Huxley's companion on the _Rattlesnake_, had published suggestions which came exceedingly near to Darwin's theory. In 1831 Mr. Patrick Matthew had published a work on _Naval Architecture and Timber_, and in it had stated the essential principle of the Darwinian doctrine of struggle and survival. Still earlier, in 1813, a Dr. W.C. Wells, in a paper to the Royal Society on "A White Female, Part of whose Skin Resembles that of a Negro," had, as Darwin himself freely admitted, distinctly recognised the principle of natural selection--but applied it only to the races of man, and to certain characters alone. Finally, long before either of these, Aristotle himself had written, in _Physics_, ii., 8: "Why are not the things which seem the result of design, merely spontaneous variations, which, being useful, have been preserved, while others are continually eliminated as unsuitable?"

None of these foreshadowings were supported by lengthy evidence, nor worked out into an elaborate theory; and it was not until Darwin had done this that we can say the birth of natural selection really took place. Huxley writes:

"The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present,--and which we call 'spontaneous,' because we are ignorant of their causation,--is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858."

But that suggestion is the central idea of the origin of species, and contains the quintessence of Darwinism.

Some weeks before the _Origin_ was published, Darwin wrote to Huxley, sending him a copy of the work, and asking him for the names of eminent foreigners to whom it should be sent. In the course of his letter he wrote: "I shall be intensely curious to hear what effect the book produces on you," and it was clear that he had no very confident expectation of a favourable opinion. Huxley replied the day before the _Origin_ was published, saying that he had finished the volume, and stating that it had completely convinced him of the fact of evolution, and that he fully accepted natural selection as a "true cause for the production of species." Darwin, in a letter to Wallace, telling of his doubts and fears concerning the reception of his book, had added the postscript: "I think I told you before that Hooker is a complete convert. If I can convert Huxley, I shall be content." When he received Huxley's letter he replied at once:

"Like a good Catholic who has received extreme unction, I can now sing _Nunc Dimittis_. I should have been more than contented with one quarter of what you have said. Exactly fifteen months ago, when I first put pen to paper for this volume, I had awful misgivings, and thought perhaps I had deluded myself, like so many have done; and I then fixed in my mind three judges, on whose decision I determined mentally to abide. The judges were Lyell, Hooker, and yourself. It was this which made me so excessively anxious for your verdict. I am now contented, and can sing my _Nunc Dimittis_."

The effect of the new theory on Huxley's mind has been expressed most fully and clearly by himself:

"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 a.s.sumed 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 zoologist, or botanist, or palaeontologist, among the mult.i.tude 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 mult.i.tudes of phenomena which are not deducible from any generalisation we have yet reached. But the same may be said of every other cla.s.s 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 acc.u.mulated, 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 pa.s.sed 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 Medusae 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 Medusae we do not repeat the observation in the case of so many different forms of Medusae as Huxley studied; but it is part of 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 mult.i.tude 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 pa.s.sages 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 att.i.tude:

"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 a.s.suredly 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 mult.i.tude 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 compet.i.tors, 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 a.s.sertion 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 palaeontology; 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:

"I am as much convinced now as I was thirty-four years ago that the theory propounded by Mr. Darwin, I mean that which he propounded--not that which has been reported to be his by too many ill-instructed, both friends and foes--has never yet been shewn to be inconsistent with any positive observations, and if I may use a phrase which I know has been objected to, and which I use in a totally different sense from that in which it was first proposed by its first propounder, I do believe that on all grounds of pure science it 'holds the field' as the only hypothesis at present before us which has a sound scientific foundation.... I am sincerely of opinion that the views which were propounded by Mr. Darwin thirty-four years ago may be understood hereafter as const.i.tuting an epoch in the intellectual history of the human race. They will modify the whole system of our thought and opinion, our most intimate convictions. But I do not know, I do not think anybody knows, whether the particular views he held will be hereafter fortified by the experience of the ages which come after us.... Whether the particular form in which he has put before us the Darwinian doctrines may be such as to be destined to survive or not, is more, I venture to think, than anybody is capable at this present moment of saying."

Further details of Huxley's relation to natural selection may be gained from an interesting chapter in Professor Poulton's volume on _Charles Darwin_ (Ca.s.sell and Co., London, 1896).