accepting it by the theological objection that it appeared to substitute the action of a physical force for the direct action of the Deity. In France, where ideas not of French origin are very apt to be but slowly apprehended, the opposition to the Newtonian theory was not silenced till 1759, when Clairaut and Lalande, by calculating the retardation of Halley's comet, furnished such crucial proof as could not possibly be overcome. At this time Newton had been thirty-two years in his grave; seventy-two years had elapsed since the publication of the Principia, and ninety-four since the hypothesis was first definitely conceived."-(Darwinism and other Essays. pp. 1-2.)

Mr. Wallace asserts that new facts fit in satisfactorily with the theory of Natural Selection, but since he wrote his Contributions to the Theory of Natural Selection, there have not been wanting experts who contend that certain facts can hardly be reconciled with the theory of Natural Selection; and it is not too much to say that a reaction against Pure Darwinism, if not against Natural Selection, has already set in.

Mr. Wallace pleads in favour of the doctrine of Natural Selection "the evidence of necessity." He meets the objection, that we have no direct evidence for the action of this selecting power in nature, thus:

"But it seems to me we have better evidence than even direct observation would be, because it is more universal-namely, the evidence of necessity. It must be so."—(Contributions. p. 309.)

The assertion that Natural Selection is a necessary truth is so far true that, if we grant its premises, the result which it predicts must necessarily take place. But the reliability of the result depends upon the correctness of the statement of the case. If you assume that the fecundity of the organic world, and the limited area for the accommodation of living forms, must lead to a struggle for existence; that this struggle for existence must exercise a selective influence in all essential respects analogous to the selection practised by the cattlebreeder and the pigeon-fancier—if you assume that this

Natural Selection will lead inevitably to the survival of the fittest, and that this survival of the fittest will necessarily lead to the transmutation of species, and has led to the evolution of all organic forms-then it might be said that Organic Evolution by means of Natural Selection is a necessary truth. It has been our endeavour to show in the First Book of this work that the assumptions of the theory do not correspond with the facts of the world in which we live; that the fertility of nature does not tend in all cases to produce a struggle for existence which is selective; that the struggle for existence is so modified in nature that it is not in many cases selective in the sense required; that where selection takes place it does not necessarily produce a transmutation of species; and Mr. Wallace himself admits, in a passage just quoted, that if the transmutation of species were brought about by the action of Natural Selection, we must not therefore infer that the same cause, acting in precisely the same way, has been the cause of Organic Evolution. Natural Selection can only be a necessary truth in so far as it is the logical outcome of certain assumptions. But if those assumptions are not true, Natural Selection cannot be a necessary law of nature.

Another argument used by Mr. Wallace is based on what is known as the law of parsimony.

"As the survival of the fittest must inevitably weed out those whose colours are prejudicial, and preserve those whose colours are a safeguard, we require no other mode of accounting for the protective tints of arctic and desert animals.-(Contributions. p. 125.)

Professor Rolleston says of this law :

"It was known in the days of the schoolmen as the Razor of Occam, and in later days it has been styled the Law of Parsimony or Economy. . . . I know that this Regula (of Newton's) has great influence on the minds of many biologists, and I believe that its influence is

by no means always for good. Our business is to ask, not what men have laid down, but how nature operates. Can a phaenomenon have more than one cause, or can it not?"-(Scientific Papers and Addresses. vol. ii., p. 721.)

"Because one agency is proved to be a vera causa, it is not thereby proved that no other can by any possibility be competent simultaneously to produce the same effect, whatever the schoolmen, with the law of parsimony ringing in their ears, may have said to the contrary." (Ibid. p. 859.)

He then proceeds to state certain cases in which a law of parsimony has a place in nature, but he contends that this law in no case excludes the possibility of a plurality of

causes :

"Many other instances of the law of parsimony might be given ; but I know not of any which cannot be reduced under one or other of these three heads; I know of none, that is, which can be in any way held to negative the tenability of a law of plurality of causes.”(p. 723.)

If there is any sphere of nature in which a plurality of causes is at work, it is surely in the colour and coloration of animals. Heat and cold, summer and winter, light and darkness, plenty and famine; the kind no less than the amount of food; physical, chemical, and organic conditions, the inward organisation and the outward condition indicated by that significant and much-embracing term "climate"-all of these affect the colours of animals; and not unfrequently it happens that the same colour is produced by two distinct causes. Such being the case with respect to colour generally, it should not surprise us to find that protective colouring is also due to many causes as before explained. Assuming that Natural Selection is one of the causes of this phenomenon, it cannot be denied that it sometimes occurs apart from Natural Selection-as, for example, when the colour of the food-plant is seen through the skin; when the colour of the food-plant affects the blood,

so that the insect lays a green egg which hatches into a green grub. In other cases it is reasonable to suppose that changed conditions have produced a direct effect, though it may not be possible to prove that this is so. Take, for example, the case of the eland :

"A curious point in the always singular freaks of the geographical distribution of animals is to be found in connection with the eland. The eland of the Cape Colony, Orange Free State, Transvaal, Namaqualand, and Demaraland, in the old days, and the eland of the Kalahari, at the present time, were and are always entirely devoid of markings, the body-colouring varying from a dun or fawn in the younger beasts to a bluish buff in the old animals. In Mashunaland and Portuguese South-eastern Africa and beyond the Zambesi-in all parts of Africa where elands are to be found-they are met with, bearing invariably a number of white stripings across the body--very similar to the markings of the koodoo-and are marked also with a black patch on the outer side of the fore-arm, and a dark list running down the spine. These characteristic stripings are entirely wanting in the eland of South-western Africa, which from the rapid narrowing of its habitat and its constant persecution, is, as I have pointed out, likely not long hence to vanish altogether. That the absence of stripings has accompanied a more desert and waterless, more temperate and less tropical habitat, is a plain fact enough. And that the stripings appear in all elands throughout the more tropical parts of Africa is also perfectly apparent. To explain the variation is a much more difficult matter. Possibly heat and moisture have something to do with it. This, however, is a difficult and a thorny subject, and even Darwin himself was oftentimes puzzled to account for the capricious nature of the markings and stripings of animals.”— (H. A. Bryden. Chambers' Journal. vol. xi., 5th series, p. 674.— The Vanishing Eland.)

No doubt the markings are capricious from the point of view of Natural Selection, but if we knew all the effects of external conditions and of internal organisation, we should see that every mark had its obvious cause.

What are we to understand Mr. Wallace to mean when he tells us that having found, as he believes, that protective colouring can be produced by Natural Selection, we may rest content and need seek no other cause for the phenomenon? Remembering that this is a case in which the

EE

principle of a plurality of causes is evidently at work, are we to be content with the assertion which is only a fraction of the truth, if it be a truth at all, that protective colouring is the result of Natural Selection? Ought we not to wish to know the truth, the whole truth? We cannot suppose that Mr. Wallace wished to arrest further enquiry in the interests of the theory which he espoused. Such a treatment of the subject would only be justified if nature was known to work always on the principle of “one effect, one cause."

There is one other consideration to be borne in mind, namely, that the supposed law of parsimony, in asserting that a given cause is sufficient, by itself, to explain a given result without reference to other causes, always assumes that this cause is a true cause. I have given reasons for my belief that Natural Selection is not the true cause of protective colouring. If this is so, the application of the law of parsimony to this case would lead not merely to the inculcation of a half truth, but to the preservation of error. In no aspect of this subject can the argument be regarded as worthy of the true scientific spirit.

There is but one proof which is worth anything with respect to a scientific theory of physical nature, and this is a rigid comparison of its assumptions with the actual phenomena. In the earlier part of this work I gave reasons for believing that the theory of Natural Selection would not bear this test. It is unnecessary to go over this ground again, except to say this: that if Natural Selection is not proved to be active now in the transmutation of species, it deprives us of all right to assume that it has been active through untold eras in bringing about the process of Organic Evolution.

And now we come to what seems to me the most astounding argument which was ever urged in defence of