LORD SALISBURY ON EVOLUTION1

ENTHUSIASTIC adherents have compared the principle of natural selection with the principle of gravitation. The comparison is not warranted. In the first place the one is far from having a like cardinal value with the other as a scientific truth; and in the second place it is not the sole cause of the phenomena to be explained, as Mr. Darwin himself admitted when recognising the inherited effects of use and disuse. Nevertheless, after making these reservations, I will for a moment adopt the comparison; because, by its aid, I shall be enabled clearly to show the nature of a widely prevalent misconception.

Let us suppose that our days were the days when Newton had lately propounded his theory, and that the newspaper reader (or as there were few such in those days, let us say the man in the street') had been told about it. Suppose it had been explained to him that, according to Newton, bodies attract one another directly as their masses and inversely as the squares of their distances, and that the phenomena presented by the Solar System had been accounted for by him as conforming to this law. Suppose that presently the man, thus far instructed, learned that there were sceptics: Clairaut, for instance, having found that certain of the Moon's motions could not be explained as results of gravitation, and that consequently Newton's interpretation of planetary motions was untenable. Now suppose the man inferred that along with the theory of gravitation the theory of the Solar System must be abandoned; and that certain views of Copernicus, of which he had heard, and certain other views of Kepler, had been disproved. What, in such case, should we say? Evidently that the man made a profound mistake in identifying the theory of gravitation with the theory of the Solar System. We should say that there were independent reasons for accepting the Copernican system and the laws of Kepler; and that though, were the law of gravitation disproved, the pre-existing theory of the Solar System would lack that rational interpretation which the law of gravitation. gave to it, yet it would remain standing on conclusive evidence.

Mr. Darwin's doctrine of natural selection and the doctrine of organic evolution are, by most people, unhesitatingly supposed to be 1 Inaugural Address to the British Association, 1894.

one and the same thing. Yet between them there is a difference analogous to that between the theory of gravitation and the theory of the Solar System; and just as the theory of the Solar System, held up to the time of Newton, would have continued outstanding had Newton's generalisation been disproved, so, were the theory of natural selection disproved, the theory of organic evolution would remain. Whether it were shown that natural selection is inoperative, or whether it were shown that though a partial cause it is inadequate to explain all the facts (the inheritance of functionally-wrought modifications being a co-operative cause); or whether it were shown that no cause hitherto alleged is adequate; the general doctrine that organisms of all kinds have arisen by the continual superposing of modifications upon modifications would maintain its place, though it would not be fortified so strongly. Lord Salisbury, however, in common with the immense majority of men, assumes that the hypothesis of organic evolution must stand or fall with its alleged causal agencies. Though in one paragraph he distinguishes between natural selection as an alleged agent, and the facts regarded as implying evolution which are said to be explained by it, yet, at the close of his address, he assumes the two to be so indissolubly connected that, if natural selection goes, evolution must go with it-that the facts are not naturally explicable at all, but must be regarded as supernatural. He says, referring to Professor Weismann :-'I quite accept the Professor's dictum that if natural selection is rejected we have no resource but to fall back on the mediate or immediate agency of a principle of design.' And thus he endorses the popular notion that Darwinism and Evolution are equivalent terms.

Though, speaking on behalf of biologists, who are conscious of the difference, Professor Huxley, in seconding the vote of thanks, demurred to this identification, yet the above-quoted sentence reappears in the revised and republished form of Lord Salisbury's address.

Absence of direct proof of natural selection is duly emphasised by Lord Salisbury. He says:-'No man or succession of men have ever observed the whole process in any single case, and certainly no man has recorded the observation.' And, as direct proof of the hypothesis is not forthcoming, it is tacitly assumed that we must accept the alternative hypothesis, which is equally without direct proof. Here I may be excused if, à propos of this position, I reproduce some passages from an essay published in pre-Darwinian days, when the development hypothesis, as it was then called, was universally ridiculed. The first part of the essay runs as follows:

In a debate upon the development hypothesis, lately narrated to me by a friend, one of the disputants was described as arguing that as, in all our experience, we know no such phenomenon as transmutation of species, it is unphilosophical to assume that transmutation of species ever takes place. Had I been present I think that, passing over his assertion, which is open to criticism, I should have replied

that, as in all our experience we have never known a species created, it was, by his own showing, unphilosophical to assume that any species ever had been created.

Those who cavalierly reject the Theory of Evolution as not being adequately supported by facts, seem to forget that their own theory is supported by no 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 assume 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 which have become extinct, we may safely estimate the number of species that have existed, and are existing, on the Earth, at not 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 [each implying a conscious design and acts in pursuance of it]? or is it most likely that, by continual modifications due to change of circumstances, ten millions of varieties [i.e. kinds] have been produced? . . .

Doubtless many will reply that they can more easily conceive ten millions of special creations to have taken place, than they can conceive that ten millions of varieties have arisen by successive modifications. All such, however, will find, on inquiry, that they are under an illusion. . . . Careful introspection will show them that they have never yet realised to themselves the creation of even one species. If they have formed a definite conception of the process, let them tell us how a new species is constructed, and how it makes its appearance. Is it thrown down from the clouds? or must we hold to the notion that it struggles up out of the ground? Do its limbs and viscera rush together from all the points of the compass? or must we receive the old Hebrew idea, that God takes clay and moulds a new creature?...

Should the believers in special creations consider it unfair thus to call upon them to describe how special creations take place, I reply that this is far less than they demand from the supporters of the development hypothesis. They are merely asked to point out a conceivable mode. On the other hand, they ask, not simply for a conceivable mode, but for the actual mode. They do not say-Show us how this may take place; but they say-Show us how this does take place. So far from its being unreasonable to put the above question, it would be reasonable to ask not only for a possible mode of special creation, but for an ascertained mode; seeing that this is no greater a demand than they make upon their opponents.

It is true that the contrast of evidences here emphasized refers not to the theory of the origin of species through natural selection, which at that time (1852) had not been propounded, but refers to the theory of organic evolution considered apart from any assigned causes, or rather, as due to the general cause-adaptation to conditions. The contrast remains equally strong, however, if, instead of the general doctrine the special doctrine is in question; and the demand for facts in support of this special doctrine may similarly be met by the counter-demand for facts in support of the doctrine opposed to it. Perhaps Lord Salisbury will meet this demand by quoting the statements contained in the book of Genesis. But even if, ignoring the scepticism of professed biblical critics, such as the Rev. Professor Cheyne, he puts absolute faith in these statements current among nomadic groups of shepherds three thousand years ago, he is obliged to admit that these alleged facts are not of the class he refers to when

he asks for proof of the hypothesis of natural selection: they are not facts of direct observation.

Thus, supposing the two hypotheses-special creation and evolution by natural selection—are to be tested by the directly observed facts assigned in their support, then, if the hypothesis of evolution by natural selection is to be rejected because there are no directly observed facts which prove it, the hypothesis of special creation must be rejected for the same reason. Nobody has seen a species evolved and nobody has seen a species created.

But now from the question of direct evidence let us pass to the question of indirect evidence. Let us ask if there are any positive facts of observation which tend to justify the one, and whether there are any positive facts of observation which tend to justify the other. Here a comparison leads to widely different results. Familiar though some of the facts are, I must be excused for specifying them, since Lord Salisbury ignores them.

Though, because most of the geological record has been destroyed while the remnant has been dislocated or blurred, and because so small a part—an infinitesimal part of this remnant has been examined, paleontology furnishes but broken evidence, yet the more the Earth's strata are examined the more they testify that organic forms have arisen by modifications upon modifications. Recent discoveries, especially those which show by intermediate forms that the bird-type is derived from the reptile-type, and those which show that, beginning with the four-toed Orohippus of the Eocene strata, we ascend in later strata, through Mesohippus, Miohippus, Protohippus, and Pliohippus, up to the modern horse, have given strong support to the hypothesis of evolution: support so strong that Professor Huxley, who had up to the time he saw Professor Marsh's fossils made reservations in his acceptance of the hypothesis, thereafter accepted it without reserve. Not only do fossils furnish in this and other cases the lines of linear ascent to existing forms, but they simultaneously disclose a general fact of great significance-the fact that early types of creatures in any class display the commonest or most general traits of structure, and that later types of the same class are more specialised in this or that direction: relationships which are necessarily implied by the evolutionary process of divergence and re-divergence with accompanying modifications.

The truths of classification, again, have a kindred meaning. Ordinary people, and even naturalists of the old school, pass by as of no significance the remarkable relations which, in both plant and animal kingdoms, exist among their divisions, sub-divisions, and subsub-divisions--their classes, sub-classes, cohorts, orders, genera, species, varieties. The fact that these fall into groups within groups, successively decreasing in size, consists perfectly with the supposition of

common origin. Suppose an arm of a large tree to have been buried in such wise as to leave only the tips of its twigs visible; and suppose a man from the Faroe Isles, ignorant of trees, taking one of these protruding tips for a separate plant, attempted to uproot it. He would find that below the surface the twig he uncovered joined with others like itself to form a small branch; and explorations all around would prove that everywhere the local clusters of twigs thus converged. Further excavations would show that the adjacent branchlets, composed of clusters of twigs, themselves united a little deeper down, and were sub-divisions of a medium-sized branch. Again digging he would discover that several such branches formed parts of a still larger branch; and so on continually, until complete clearance made it manifest that all these great branches, small branches, branchlets, and twigs, in their respective groups, had diverged from the one original arm of the tree, which itself had diverged from the stem; and that they formed groups within groups diminishing in size as they became more remote from their common parent. And now observe that while there are thus symbolized the relationships of species, genera, orders, &c., as they now exist, there are also symbolized the relationships which, so far as we know them, exist among remains contained in the Earth's crust: the two sets of phenomena correspond.

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The lesson taught by the facts of distribution in Time, is also taught by the facts of distribution in Space. In various regions there are alliances between the present fauna and the past fauna found fossil: though different, they are near akin. It was this wonderful relationship in the same continent between the dead and the living' which especially forced on Mr. Darwin the belief in descent with modification: this relationship having been demonstrated by Professor Owen between the existing South American forms and the buried forms of extinct species. The fact that in Australia, long cut off from the other continents, all the indigenous mammals are of the implacental type, and that the fossil mammals found there are also exclusively implacental, illustrates these connections very clearly. And these likenesses of nature between present faunas and past faunas in the same localities are implications agreeing exactly with the implications pointed out above.

Once more there are the facts of embryology. In various ways these tell us with endless repetition the same story.

Von Baer'found that in its earliest stage, every organism has the greatest number of characters in common with all other organisms in their earliest stages; that at a stage somewhat later, its structure is like the structures displayed at corresponding phases by a less extensive multitude of organisms; that at each subsequent stage, traits are acquired which successively distinguish the developing embryo from groups of embryos that it previously resembled thus step by step diminishing the class of embryos which it still resembles; and that thus the class of similar forms is finally narrowed to the species of which it is a member.'