5; 



NATURE 



[Sept. 26, 1889 



and accident. I shall take as my example certain facts which 

 are well known to those engaged in the breeding of farm-stock or 

 of other animals that are of utility to or are specially cultivated 

 by man. 



I do not refer to the influence on the offspring of impressions 

 made on the senses and nervous system of the mother, the first 

 statement of the effects of which we find in the book of Genesis, 

 where Jacob set peeled rods before the flocks in order to influence 

 the colour and markings of their young ; though I may state that I 

 have heard agriculturists relate instances from their own expe- 

 rience which they regarded as bearing out the view that im- 

 pressions acting through the mother do influence her offspring. 

 But I refer to what is an axiom with those who breed any 

 particular kind of stock, that to keep the strain pure, there must 

 be no admixture with stock of another blood. For example, if 

 a shorthorned cow has a calf by a Highland sire, that calf, of 

 course, exhibits characters which are those of both its parents. 

 But future calves which the same cow may have when their sires 

 have been of the shorthorned blood, may, in addition to short- 

 horn characters, have others which are not shorthorned but High- 

 land. The most noteworthy instance of this transmission of 

 characters acquired from one sire through the same mother to her 

 offspring by other sires is that given in the often-quoted experi- 

 ment by a former Lord Morton.^ An Arabian mare in his 

 possession produced a hybrid the sire of which was a quagga, 

 and the young one was marked by zebra-like stripes. But 

 the same Arabian had subsequently two foals, the sire of 

 which was an Arab horse, and these also showed some zebra- 

 like markings. How, then, did these markings characteristic 

 of a very different animal arise in these foals, both parents 

 of which were Arabians? I can imagine it being said that this 

 was a case of reversion to a very remote striped ancestor, common 

 alike to the horse and the quagga. But, to my mind, no such far- 

 fetched and hypothetical explanation is necessary. The cause of 

 the appearance of the stripes seems to me to be much nearer and 

 more obvious. I believe that the mother had acquired, during 

 her prolonged gestation with the hybrid, the power of transmit- 

 ting quaggalike characters from it, owing to the interchange of 

 material which had taken place between them in connection with 

 the nutrition of the young one. For it must be kept in mind 

 that in placental mammals an interchange of material takes place 

 in opposite directions, from the young to the mother as well as 

 from the mother to the young.'- In this way the germ-plasm of 

 the mother, belonging to ova which had not yet matured, had 

 become modified whilst still lodged in the ovary. This acquired 

 modification had influenced her future offspring, derived from 

 that germ-plasm, so that they in their turn, though in a more j 

 diluted form, exhibited zebra like markings. If this explanation | 

 be correct, then we have an illustration of the germ-plasm 

 having been directly influenced by the soma, and of somatogenic i 

 acquired characters having been transmitted. i 



But there are other facts to show that the isolation of the germ- j 

 cells or germ-plasm from the soma cells is not so universal as might 

 at the first glance be supposed. Weismann himself admitsthat 

 in the Hydroids the germ-plasm is present in a very finely 

 divided, and therefore invisible, state, in certain somatic cells in 

 the beginning of embryonic development, and that it is then 

 transmitted through innumerable cell generations to those remote 

 individuals of the colony in which sexual products are formed. 

 The eminent botanist Prof. Sachs states that in the true mosses 

 almost any of the cells of the roots, leaves, and shoot axes may 

 form new shoots and give rise to independent living plants. 

 Plants which produce flowers and fruit may also be raised from 

 the leaves of the Begonia. I may also refer to what is more or 

 less familiar to everybody, that the tuber of the potato can give 

 rise to a plant which bears flowers and fruit. Now in all these cases 

 the germ-plasm is not collected in a definite receptacle isolated 

 from the soma, but is diffused through the cells of the leaves of 

 the Begonia or amidst those of the tuber of the potato, and the 

 propagation of the potato may take place through the tuber for 

 several generations without the necessity of having to recur to 

 the fruit for seed. It seems difficult, therefore, to understand 

 why, in such cases, the nutritive processes which affect and 

 modify the soma cells should not also react upon the germ plasm, 

 which, as Weismann admits, is so intimately associated with 

 them. 



I Philosophical Transactions, 1881 : also Darwin's "Animals and Plants 

 under Domestication," first edition, vol. i. p. 403, 1868, 



- See, for example. Essays bv Profs. Harvey and Gusserow and Mr.^ 

 Savory ; also my " Lectures on the Comparative Anatomy of the Placenta" 

 (Edinburgh, 1876). 



Those who uphold the view that characters acquired by the 

 soma cannot be transmitted from parents to offspring undoubtedly 

 draw so large a cheque on the bank of hypothesis that one finds 

 it difficult, if not impossible, to honour it. Let us consider for 

 one moment all that is involved in the acceptance of this theory, 

 and apply it in the first instance to Man. On the supposition 

 that all mankind have been derived from common ancestors 

 through the continuity of the germ-plasm, and that this plasm 

 has undergone no modification from the peisona or sojua of the 

 succession of individuals through whom it has been transmitted, 

 it would follow that the primordial human germ-plasm must have 

 contained within itself an extraordinary potentiality of develop- 

 ment — a potentiality so varied that all those multiform variations 

 in physical structure, tendency to disease, temperament, and 

 other characters and dispositions which have been exhibited by 

 all the races and varieties of men who either now inhabit or at 

 any period in the world's history have inhabited the earth, must 

 have been included in it. But if we are to accept the theory of 

 Natural Selection, as giving a valid explanation of the origin of 

 new species, then the non-transmissibility of somatogenic 

 acquired characters has a much more far-reaching significance. 

 For if all the organisms, whether vegetable, animal, or human, 

 which have lived upon the earth have arisen by a more or less 

 continuous process of evolution from one or even several simple 

 cellular organisms, it will follow, as a logical necessity of the 

 theory, that these simple organisms must have contained in their 

 molecular constitution a potentiality of evolution into higher and 

 more complex forms of life, through the production of variations, 

 without the intermediation of any external force or influence 

 acting directly upon the soma. Further, this must have endured 

 throughout a succession of countless individual forms and species, 

 extending over we know not how many thousands of years, and 

 through the various geological and climatic changes which have 

 affected the globe. 



The power of producing these variations would therefore, on 

 this theory, have been from the beginning innate to the germ- 

 plasm, and uninfluenced in any way by its surroundings. 

 Variations would have arisen spontaneously in it, and, for any- 

 thing that we know, as it were by accident, and without a 

 definite purport or object. But whether such variations would 

 be of service or dis-service could not be ascertained until after 

 their appearance in the soma had subjected them to the test 

 of the conditions of life and the environment. 



Let us now glance at the other side of the question. All 

 biologists will, I suppose, accept the proposition that the 

 individual soma is influenced or modified by its environment or 

 surroundings. Now, if on the basis of this proposition the theory 

 be grafted that modifications or variations thus produced are 

 capable of so affecting the germ-plasm of the individual in 

 whom the variation arises as to be transmitted to ils off- 

 spring — and I have already given cases in point — then such 

 variations might be perpetuated. If the modification is of 

 service, then presumably it will add to the vitability of the 

 individual, and through the interaction between the soma and 

 the germ-plasm, in connection with their respective nutritive 

 changes, will so affect the latter as to lead to its being transmitted 

 to the offspring. From this point of view the environment would, 

 I as it were, determine and regulate the nature of those variations 

 which are to become hereditary, and the possibility of variations 

 arising which are likely to prove useful becomes greater than 

 on the theory that the soma exercises no influence on the germ- 

 1 plasm. Hence I am unable to accept the proposition that 

 i somatogenic characters are not transmitted, and I cannot but 

 I think that they form an important factor in the production of 

 I hereditary characters. 



To reject the influence which the use and disuse of parts may 

 : exercise both on the individual and on his offspring is like look- 

 \ ing at an object with only a single eye. The morphological 

 { aspect of organic structure is undoubtedly of fundamental im- 

 I portance. But it should not be forgotten that tissues and organs, 

 in addition to their subjection to the principles of development 

 and descent, have to discharge certain specific purposes and 

 functions, and that structural modifications arise in them in cor- 

 relation with the uses to which they are put, so as to adapt them 

 to perform modified duties. It may be difficult to assign the 

 exact value which physiological adaptation can exercise in the- 

 perpetuation of variations. If the habit or external condition 

 which has produced a variation continues to be practised, then, 

 in all probability, the variation would be intensified in successive 

 generations. But should the habit cease or the external condi- 



