September 3, 1908] 



NA TURE 



421 



[iiay show a blend of both parental characters. Senion ' 

 use's as a model the two versions of Goethe's poem— 



/ Wiildern, hOrest du, keinen 



" Ueber alien Gipfelii, ^t K"ti- i" a"«" •. \\ i,,f"ln, ' spiirest du, kaum 



( eiiiKn Hauch." 



Onu of these terminations will generally be prc-potent, 

 probably the one that was heard first or heard most often. 

 Hut the cause of such pn-potency may be as obscure as the 

 corresponding occurrence in the formation of mongrels. 

 We can only say that in some persons the word " alien " 

 releases the word " Wiildern," while in others it leads up 

 to " Wipfeln." ."Vgain, a mi.xture of the terminations may 

 occur leading to such a mongrel form as : " in alien 

 Waldern horest du kaum einen Hauch." The same thing 

 is true of music ; a man with an imperfect memory easily 

 interpolates in a melody a bar that belongs clsew-herc. In 

 the case of memory the introduction of a link from one 

 mental rhythm into another can only occur when the two 

 series are closely similar, and this may remind us of the 

 difficulty of making a cross between distantly related 

 forms. 



Enough has been said to show that there is a resemblance 

 between the two rhythms of development and of memory ; 

 and that there is at least a frima facie case for believing 

 them to be essentially similar. It will be seen that my 

 view is the same as that of Hering, which is generally 

 described as the identification of memory and inheritance." 

 Hering says that " between the me of to-day and the me 

 of yesterday lie night and sleep, abysses of unconscious- 

 ness ; nor is there any bridge but memory with which to 

 span them." .And in the same way he claims that the 

 abyss between two generations is bridged by the 

 unconscious memory that resides in the germ-cells. It is 

 also the same as that of Scmon and to a great extent as 

 that of Rignano.' I, however, prefer at the moment to 

 limit myself to asserting the identity of ontogeny and habit, 

 or, more generally, to the assertion in Semon's phrase- 

 ology, that ontogeny is a mnemic phenomenon. 



Evolution, in its modern sense, depends on a change in 

 the ontogenetic rhythm. This is obvious, since if this 

 rhythm is absolutely fixed, a species can never give rise 

 to varieties. This being so, we have to ask in what ways 

 the ontogenetic rhythm can be altered. An habitual action, 

 for instance, a trick learned by a dog, may be altered by 

 adding new accomplishments ; at first the animal will 

 persist in finishing his performance at the old place, but 

 at last the extended trick will be bonded into a rhythm 

 of actions as fixed as was the original simpler perform- 

 ance. May we not believe that this is what has occurred 

 in evolution? 



We know from experiment that a plant may be altered 

 in form by causes acting on it during the progress of 

 development. Thus a beech tree may be made to develop 

 different forms of leaves by exposing it to sunshine or to 

 shade. The ontogeny is different in the two cases, and 

 what is of special interest is, that there exist shade-loving 

 plants in which a structure similar to that of the shaded 

 beech-leaf is apparently typical of the species, but on this 

 point it is necessary to speak with caution. In the same 

 way Goebel points out that in some orchids the assimil- 

 ating roots take on a flattened form when exposed to 

 sunlight, but in others this morphological change has 

 become automatic, and occurs even in darkness.* 



Such cases suggest at least the possibility of varieties 

 arising as changes in or additions to the later stages of 

 ontogeny. This is, briefly given, the epigenctic point of 

 view. 



But there is another way of looking at the matter — 

 namely, that upheld by Galton and Weismann. .Accord- 

 ing to this view ontogeny can only be changed by a funda- 

 mental upset of the whole system — namely, by an altera- 



^ " Die Mneme," 2nd edit., pp. 147. ?2i. 303, 345. 

 _ 2 F.veryrne who deals with ihi"; subject must lake his stand on the founda- 

 tion laid hy Herin? in his celebrated address jii-n at Vienna in 1870 and 

 reprinted in No. 148 of Cistwald's Exakt Klassiker. The passage quoted 

 (p. 14) i? from Samuel Butler's translation of Hering in "Unconscious 

 Memory," i83o, p. iio. Butler had previously elaborated the view that " we 

 are one person with our ancestors " in his entertaining book " Life and 

 Habit." 1878, and this was written in ignorance of Hering's views, 



■* " Sur la Transmissihilite des Caracieres arqui-," Paris, 1506. 



■* Goebel's " Organography of Plants." part ii., p. 285, 



KO. 2027, VOL. 78] 



tion occurring in its first stage, the germ-cell, and this 

 view is now very generally accepted. 



The same type of change may conceivably occur in 

 memory or habit, that is, the rhythm as a whole may be 

 altered by some cause acting on the nerve-centres con- 

 nected with the earlier links of the series. The analogy 

 is not exact, but such an imaginary case is at least of a 

 different type from a change in habit consisting in the 

 addition of a new link or the alteration of one of the latest 

 formed links. If we were as ignorant of the growth of 

 human actions as we are of variation, we might have a 

 school of naturalists asserting that all changes in habit 

 originate in the earliest link of the series. Uut we know 

 that this is not the case. On the other hand, I fully admit 

 that the structure of an ovum may in this way be altered, 

 and give rise to a variation which may be the starting- 

 point of a new species. 



But how can a new species originate according to an 

 epigenetic theory? How can a change in the latter stages 

 of ontogeny produce a permanent alteration in the germ- 

 cells? Our answer to this question will depend on our 

 views of the structure of the germ-cells. According to the 

 mnemic theory they have the quality which is found in 

 the highest perfection in nerve-cells, but is at the same 

 time a character of all living matter — namely, the power 

 of retaining the residual effects of frjrmcr stimuli and of 

 giving forth or reproducing under certain conditions an 

 echo of the original stimulus. In Semon's phraseology 

 gerin-cclls must, like nerve-cells, contain cngrams, and 

 these engrams must be (like nerve-engrams) bonded 

 together by association, so that they come into action one 

 after another in a certain order automatically, i.e., in the 

 absence of the original stimuli. 



This seems to me the strength of the mnemic theory — 

 namely, that it accounts for the preformed ch.aracter of 

 germ-cells by the building up in them of an organised 

 series of engrams. But if this view has its strength, it 

 has also its weakness. Routine can only be built up by 

 repetition, but each stage in ontogeny occurs only once 

 in a lifetime. Therefore if ontogeny is a routine each 

 generation must be mnemically connected with the next. 

 This can only be possible if the germ-cells are, as it were, 

 in telegraphic communication with the whole body of the 

 organism ; so that as ontogeny is changed by the addition 

 of new characters, new engrams are added to the germ- 

 cell. 



Thus in fact the mnemic theory of development depends 

 on the possibility of what is known as somatic inherit- 

 ance or the inheritance of acquired characters. This is 

 obvious to all those familiar with the subject, but to others 

 it may not be so clear. Somatic inheritance is popularly 

 interesting in relation to the possible inherited effects of 

 education, or of mutilations, or of the effects of use and 

 disuse. It is forgotten that it may be, as I have tried 

 to show, an integral part of all evolutionary development. 



Weismann' s Theory. 



Everyone must allow that if VVcismann's theory of 

 inheritance is accepted we cannot admit the possibility of 

 somatic inheritance. This may be made clear to those 

 unfamiliar with the subject by an illustration taken from 

 the economy of an ant's nest or beehive. The queen ' on 

 whom depends the future of the race is cut off from all 

 active experience of life : she is a mere reproducing 

 machine, housed, fed, and protected by the wcjrkers. But 

 these, on whom falls the burden of the struggle for life 

 and the experience of the world generally, are sterile, and 

 take no direct share in the reproduction of the species. The 

 queen represents Weismann 's germ-plasm, the workers are 

 the body or soma. Now imagine the colony exposed to 

 some injurious change in environment ; the salvation of 

 the species will depend on whether or no an improved 

 pattern of worker can be produced. This depenrjs on the 

 occurrence of appropriate variations, so that the queen 

 bee and the drones, on whom this depends, are of central 

 importance. On the other hand any change occurring in 

 the workers, for instance, increased skill due to practice in 

 doing their work or changes in their structure due to 

 external conditions, cannot possibly be inherited, since 



t Kor do the drones share the activity of the workrrs. 



