Attgtist 25, 1887] 



NATURE 



405 



I 



the facts both of progress and of regress. But, unless we are 

 -atisfied to walk upon the high priori road to the exclusion of 

 every other, we must not too readily assume that the presence 

 and the absence of selection have been the only factors at 

 work. In particular, we have now to consider whether use and 

 disuse have co-operated with the presence and the absence 

 of selection in bringing about the existing state of matters 

 in organic Nature as a whole. 



Now, the only way in which this inquiry can be conducted is 

 by the method of difference. We must search through organic 

 Nature in order to ascertain whether there are any cases either of 

 evolution or of degeneration where it is manifestly impossible 

 that either the presence or the absence of selection can have had 

 anything to do with the process. If we can find any such cases, we 

 -;hall not merely save Darwin from his friends by justifying his 

 acceptance of the Lamarckian assumption : we shall prove that 

 presumably in all cases where the presence or the absence of 

 selection has been concerned in either building up or breaking 

 down organic structures, these principles have been largely 

 assisted in their operations by the inherited effects of use and 

 lisuse. For if it can be proved that these effects are inherited 

 in cases where it is impossible that the principle of selection — 

 or its cessation — can have obtained, it would be irrational to. 

 deny that they are also inherited in other cases where these 

 principles do obtain. 



Seeing that so accomplished a naturalist and so philosophic a 

 thinker as Prof. Weismann has declared that there is no one case 

 to be found such as those of which we are in search, we must be I 

 prepared to expect some difficulty in meeting with examples of 

 the uncompounded influence of use and disuse — even supposing 

 use and disuse to be the true causes of specific modification that 

 they were taken to be by Darwin. In order to show the kind of 

 difficulty that here besets inquiry, I will quote a passage from 

 Mr. Spencer's recently-published essay upon the subject. 



" When discussing the question more than twenty years ago 

 \' Principles of Biology,' § 166), I instanced the decreased size of 

 the jaws in the civilised races of mankind as a change not 

 accounted for by the natural selection of favourable variations ; 

 since no one of the decrements by which, in thousands of years, 

 ihis reduction has been effected would have given to an individual 

 in which it occurred such advantage as would cause his survival, 

 either through diminished cost of local nutrition or diminished 

 weight to be carried. . . , Reconsideration of the facts 

 • loes not show me the invalidity of the conclusion drawn, that 

 tins decrease in the size of the jaw can have had no other cause 

 than continued inheritance of those diminutions consequent on 

 diminutions of function, implied by the use of selected and well- 

 prepared food. Here, however, my chief purpose is to add an 

 instance showing, even more clearly, the connection between 

 change of function and change of structure. This instance, 

 allied in nature to the other, is presented by those varieties — or, 

 rather, sub- varieties — of dogs, which, having been household 

 pets, and habitually fed on soft food, have not been called upon 

 to use their jaws in tearing and crunching, and have been but 

 rarely allowed to use them in catching prey and in fighting." 



There follows an account of a somewhat laborious examination 

 of dogs' skulls in the Museum of Natural History, the result of 

 which was to show that "we have two, if not three, kinds of 

 dog, which, similarly leading protected and pampered lives, show 

 that in the course of generations the parts concerned in clenching 

 the jaws have dwindled ; " after which the passage proceeds as 

 follows : — 



" To what cause must this decrease be ascribed? Certainly 

 not to artificial selection ; for most of the modifications named 

 make no apj^reciable external signs : the width across the 

 zygomata could alone be perceived. Neither can natural selec- 

 tion have had anything to do with it ; for even were there any 

 struggle for existence among such dogs, it cannot be contended 

 that any advantage in the struggle could be gained by an indi- 

 vidual in which a decrease took place. Economy of nutrition, 

 too, is excluded. Abundantly fed as such dogs are, the consti- 

 tutional tendency is to find places where excess of absorbed 

 nutriment may be conveniently deposited, rather than to find 

 places where the cutting down of the supplies is practicable. 

 Nor, again, can there be alleged a possible correlation between 

 these diminutions and that shortening of the jaws which has 

 probably resulted from selection ; for in the bull-dog, which has 

 also relatively short jaws, the structures concerned in closing 

 them are unusually large. Thus, there remains as the only 

 conceivable cause, the diminution of size which results from 

 diminished use." 



Evidently Mr. Spencer has never heard or thought of the 

 cessation of selection, either as explained thirteen years ago by 

 myself, or as republished within the last few months by Prof. 

 Weismann. For it is evident that, far from his having excluded all 

 conceivable causes of the diminution save that of diminished use, 

 it would be difficult to find a case more favourable to the influence 

 of the cessation of selection. The dogs in question have been 

 " habitually fed on soft food, have .not been called on to use 

 their jaws in tearing and crunching," and have been but rarely 

 allowed to use them in catching prey and in fighting." In other 

 words, for at least a hundred generations these dogs have been 

 "leading protected and pampered lives," wholly shielded from 

 the struggle for existence and survival of the fittest. Never 

 having had to use their jaws either in " tearing, crunching, 

 catching prey, or fighting," they, more than any other dogs — 

 even of domesticated breeds — have not been " called on " to use 

 their jaws for any life-serving purpose. Clearly, therefore, if 

 the cessation of selection ever acts at all as a reducing cause in 

 species, here is a case where it is positively bound to act. And, 

 of course, the same remark applies to the analogous case of the 

 diminished size of the jaws in civilised man. 



Be it observed, I am not disputing that disuse may in both 

 these cases have co-operated with the cessation of selection ia 

 bringing about the observed result. Indeed, I am rather dis- 

 posed to allow that the large amount of reduction described in 

 the case of the dogs as having taken place in so comparatively 

 short a time, is strongly suggestive of disuse having co-operated 

 with the cessation of selection. But at present I am merely pointing 

 out that Mr. Spencer's investigations have here failed to exhibit the 

 crucial proof of disuse as a reducing cause which he assigns to. 

 them : it is not true that in these cases disuse "remains as the 

 only conceivable cause." 



Far more successful, however, is his second line of argument. 

 Indeed, to me it has always appeared, since I first encountered 

 it fifteen years ago in the " Principles of Biology," as little 

 short of demonstrative proof of the Lamarckian assumption. 

 Therefore, if, as a result of reading the passage above quoted, one 

 feels disposed to regret that before publishing it Mr. Spencer did 

 not have his attention called to Prof. Weismann's essay on the 

 cessation of selection, still more must one regret that before 

 publishing that essay Prof. Weismann should have failed to 

 remember the " Principles of Biology." For, had he done so, 

 it seems impossible that he could ever have committed himself to 

 the statement that there is no evidence of functionally-produced 

 modifications being inherited, and thus he might have been led 

 to pause before announcing — at least in its present shape — his 

 theory of germ-plasma. 



The argument whereby in my opinion Mr. Spencer succeeds 

 in virtually proving the|truth of the Lamarckian assumption is 

 expanded in his recently-published essay, from which, therefore, 

 I will quote. 



" If, then, in cases where we can test it, we find no concomi- 

 tant variation in co- operative parts that are near together — if we 

 do not find it in parts which, though belonging to different tissues, 

 are so closely united as teeth and jaws — if we do not find it even 

 when the co-operative parts are not only closely united, but are 

 formed out of the same tissue, like the crab's eye and its 

 peduncle ; what shall we say of co-operative parts which, besides 

 being composed of different tissues, are remote from one another ? 

 Not only are we forbidden to assume that they vary together, but 

 we are warranted in asserting that they can have no tendency to 

 vary together. And what are the implications in cases where 

 increase of a structure can be of no service unless there is con ■ 

 comitant increase in many distant structures, which have to join 

 it in performing the action for which it is useful ? 



" As far back as 1864 (' Principles of Biology,' § 166) I named 

 in illustration an animal carrying heavy horns — the extinct Irish 

 elk ; and indicated the many changes in bones, muscles, blood- 

 vessels, nerves, composing the fore-part of the body, which 

 would be required to make an increment of size in such horns 

 advantageous. Here let me take another instance — that of the 

 giraffe : an instance which I take partly because, in the sixth [last] 

 edition of the ' Origin of Species,' issued in 1872, Mr. Darwin 

 has referred to this animal when effectually disposing of certain 

 arguments urged against his hypothesis. He there says : — 



" ' In order that an animal should acquire some structure 

 specially and lai^ely developed, it is almost indispensable that 

 several other parts should be modified and co-adapted. Although 

 every part of the body varies slightly, it does not follow that the 

 necessary parts should always vary in the right direction and to 

 the right degree ' (p. 1 79). 



