lO 



NATURE 



[November i, 1894 



Regard it as spontaneou;, as due to no external cause, than if it 

 appeared in mature life. The embryo in the case of a child is 

 no doubl protected from many external stimuli ; hut surely in 

 the case even of the placental mammalia it would not be safe to 

 aver that the embr)'o is protected from all external stimuli. In 

 the case of an insect, the greater part of its development takes 

 place under an exposure to external influences as complete as 

 that of the adult insect ; in the case of reproduction by gemm.'e 

 of multicellular animals, the protection must, I suppose, often 

 be small or nothing at all ; and in the case of the reproduction 

 of the lower plants from gemmae or from protonem.-i, or of the 

 higher plants by buds or from suckers, the embryonic condilion, 

 if it can be spoken of at all, is, I suppose, hardly distinguished 

 as regards the influence of external stimuli from any other part 

 of the career of the organism ; so that I find myself unable to 

 reach clear ground for the distinction between spontaneous and 

 non-spontaneous variations. 



But there are passages, to one of which I have already re- 

 ferred, which seem to suggest that the definition should be 

 framed by reference to a distinction between a direct and an in- 

 direct inlluence, and that the definition should run thus : an 

 "acquired character" is a reaction of the organism upon the direct 

 influence of a stimulus, leaving reactions upon indirect in- 

 fluences to be treated as non-acquired characters. If so, what is 

 the precise meaning of the word "direct" as applied to the 

 influence ? Does it refer to the repetition of the stimulus — so 

 that a single change of climate would be a direct, and a repeated 

 change of climate an indirect influence? Or does it refer to the 

 supposed difference between influences operating on the somatic 

 part of the organism and those which the organism itself exerts 

 on its germ plasma ? If so, I ask how is this ascertainable as a 

 physiulogical fact ? 



Another limitation on the proposition that the reactions of 

 the organism on external stimuli are acquired characters, I find 

 in the second volume of Weismann's " Essays on Heredity " 

 (English translation, p. 14), where the author, having referred 

 to the characters, such as shape and size of finger-nails, like- 

 nesses of features, bearing, gait, handwriting, which are handed 

 down from parent to child, goes on to add : "Characters only 

 acquired by the operation of external circumstancesacting during 

 the life of the individual cannot be transmitted." Now, hand- 

 writing must, I suppose, be conceived of .as a thing dependent 

 on external circumstances : it is influenced by the material on 

 which, the fluid by which, the pen or style by means of which 

 the act is performed ; but here the external circumstances have 

 operated during many generations ; so that the passage seems to 

 suggest these propositions, viz. the reactions of the organism 

 on external stimuli operating during the life of a single indi- 

 vidual arc not hereditary : the reactions of the organism 

 operating during the li%'es of two or more individuals are 

 hereditary. But such is not, I suspect, really the meaning of 

 the author ; it would be inconsistent with what he says at p. 40 

 of the same volume, where he says that the supposed increase 

 of the musical sense "in the course of generations ' by the 

 exercise of the art can only have occurred on the supposition 

 "that these modifications of an organ which are due to the 

 exercise during the individual life can be transmitted to ofl'- 

 spring" — a supposition which Prof. Wcismann says " a close 

 examination docs not allow us to admit." 



Another limitation on the class of reactions upon external 

 stimuli const ituting " acquired characters "is suggested by what I 

 conceive to be Prof. Weismann's latest utterance on the subject, 

 in his work " Das Keimplasma " (Jena, 1892). At p. 514 I find 

 him saying — " By the term acquired characters I understand 

 those which do not exist originally in the germ as tendencies, 

 but first arise through peculiar influences which operate 

 upon the body or particular paits of it. They arc the 

 leaclions of these parts upon some external influences lying 

 leyond the necessary conditions of development." ' In the first 

 o( these sentences it seems to me that the Professor is not 

 so much offering a definition as announcing a theory ; for except 

 by the inquiry whether the character is or is not heritable, I 

 suppose that there is no means of ascertaining whether or not 

 a change in the organism is due to a tendency in the germ. 



But the second sentence seems to suggest a definition of "ac- 



1 It may b: well 10 give the pavtAge in the original ; " Unter crworbenen 

 F.iRenicNafien ver«tehe icti solche. vrclche tiicht alt Anlagen schon in Kcim 



- -' — '- ■ ' . .1. -.._....'..., 1. 1-- -/^..flere Einwirkungen, die lien K-lrper 



•■nAtehen. Sic ftind die Reaclionen 

 ilialtt der ngtIiwendiKcn Mntwickc- 



junKiu^uiii^ , i,i- .. ij- ,- I ^'- ... LinHlrkiingen." 



NO. 1.305, VOL. 51] 



quired characters " free from many of the difficulties we have 

 hitherto encountered. They do not include all reactions of the 

 organism on external stimuli, but only such as lie beyond the 

 necessary conditions of development. Everything then turns 

 on the meaning of " necessary conditions of development." 

 What are necessary conditions of development ? Let us 

 lake a tree which has put forth its leaves, its flowers, its seeds, 

 in usual fashion, but which, having lost a limb by the saw of the 

 gardener, and has thrown out around the wound that growth of 

 new wood and bark with which we arc familiar. The air, the 

 sun, the soil are all external influences, and all necessary con- 

 ditions of the development which has actually occurnd, and so 

 was the saw of the gardener. If we take the development 

 which has actually occurred, every condition which led up to 

 it was necessary, and each was as necessary as the other. Take 

 the case narrated by .Sir James Paget, of a fir tree which for a 

 hundred and fifty years threw out successive annular growths 

 over the part of its trunk from which a large piece of bark had 

 been stripped off. (".\ddressto the Pathological Section of 

 the Biitish Medical .Association," iSSo, p. 15.) Were these 

 rings part of its development, or were they not ? If they were, 

 the knife or saw was one of its necessary conditions. Most 

 persons will reply that the saw was no necessary condilion of the 

 development of the fir tree, and that those only were necessary 

 conditions without which the fir tree could not have lived. 



If we consider what are the necessary conditions for the de- 

 velopment of the seed of the fir tree, we can probably ascert-tin 

 them ; but the doctrine of evolution and the doctrine of the non- 

 heritability of acquired characters will carry us back further, viz, 

 to the primordial organism, and we must ask what were the 

 necessary conditions for its development. 



If this organism were supposed to have in itself a preexisting 

 law according to which it sought development, a contingent 

 destiny inherent in its nature, then I can well undeist.and 

 how the conditions which satisfy that contingency, the circum- 

 stances which allow of that development might he said to be 

 necessary to it. But if the organism have no such law and no 

 such destiny, but instead thereof has only a capacity to vary in 

 every possible direction, and if all the course of its actual 

 variation be due to external circumstances operating by 

 means of natural selection, then it seems to me that no one 

 external thing can be said to be more essential to its develop- 

 ment than another. The germ might have found itself in a 

 diflTerent soil, in a different climate, exposed to different air, and 

 then the development of the germ would have been different. 

 There was no .'/ priori necessity that it should be exposed 

 to the particular conditions to which it w.is, in f.ict, ex- 

 posed, or to any other particular conditions. If, therefore, 

 we start from the actual development of an organism, and 

 look back on the past, all the conditions which have led to its 

 existing slate are necessary ; if we start from the germ prior to 

 all development, and look to the future, then no given condilion 

 can be said to be necessary to its development, but all are 

 contingent. 



It is suggested that no influence lying beyond the necessary 

 conditions of development can .at any time have produced any 

 heritable character, however long may have been the course of 

 development. It seems, therefore, that in order to ascertain 

 what conditions are necessary to development, we must go back 

 to the amioba or ascidian or other primx'val parent of our 

 race, and we must conclude that those char.acters only will be 

 transmissible by the human parent, which were reactions on the 

 necessary conditions of ihe development of the prim.-eval 

 ancestor. Have we any scientific means of .ascertaining what 

 these conditions were, and so of ascertaining what characters are 

 now heritable? Nay, if we adopt the evolutionary hypothesis, 

 and believe that at least all existing animal organisms have 

 sprung from a single parent, do not the diversities of Ihe exist- 

 ing forms show that no one set of external circumstances were 

 necessary conditions of development, but that the conditions 

 consistent with development were infinite, or all but infinite, in 

 number? 



A further diflicully arises in my mind from a passage on the 

 next page (p. S'S)i where I find our author mentioning 

 wounds and mutilations as constituting one category of acquired 

 characters. It is difficult to reconcile this with Ihe statement of 

 the Professor, in several passages, that acquired characters 

 are reactions of the organism ; for surely a wound is not a 

 reaction of the organism, whilst the growth of the organism 

 consequent on the wound— ^■.j'. the growth of new wood 



