24 



NATURE 



[September 3, 1914 



tion, with a slow progressive evolution due to the 

 operation of the law of accumulation of surplus 

 energy. If any of the conditions of development 

 are changed the result, as manifested in the organisa- 

 tion of the adult, must undergo a corresponding 

 modification. Suppose that the chromatin substance 

 of the zygote is partially modified in molecular con- 

 stitution, perhaps by the direct action of the environ- 

 ment, as appears to happen in the case of Tower's 

 experiments on mutation in. the potato beetle, or by 

 the introduction of a different sample of chromatin 

 from another individual by hybridisation. What is 

 the germ-plasm now going to do? When and how 

 may the changes that have taken place in its con- 

 stitution be expected to manifest themselves in the 

 developing organism? 



Let us consider what would be likely to happen in 

 the first stages of ontogeny. If the germ-plasm had 

 remained unaltered the zygote would have divided 

 into blastomeres under the stimuli of the same con- 

 ditions, both internal and external, as those under 

 which the corresponding divisions took place in pre- 

 ceding generations. Is the presence of a number of 

 new colloidal multimolecules in the germ-plasm going 

 to prevent this? The answer to this question probably 

 depends partly upon the proportion that the new multi- 

 molecules bear to the whole mass, and partly upon the 

 nature of the modification that has taken place. If 

 the existence of the new multimolecules is incom- 

 patible with the proper functional activity of the 

 germ-plasm as a whole there is an end of the matter. 

 The organism does not develop. If it is not incom- 

 patible we must suppose that the zygote begins its 

 development as before, but that sooner or later the 

 modification of the germ-plasm will manifest itself in 

 the developing organism, in the first instance as a 

 mutation. In cases of hybridisation we may get a 

 mixture in varying degrees of the distinguishing 

 characters of the two parent forms, or we mav get 

 complete dominance of one form over the other in 

 the hybrid generation, or we may even get some new 

 form, the result depending on the mutual reactions 

 of the different constituents of the germ-plasm. 



The organism into which any zygote develops must 

 be a composite body deriving its blastogenic characters 

 from different sources; but this cannot affect its 

 fundamental structure, for the two parents must have 

 been alike in all essential respects or they could not 

 have interbred, and any important differences in the 

 germ-plasm must be confined to the "factors" for 

 the differentiating characters. The fundamental 

 structure still develops epigenetically on the basis of 

 an essentially similar germ-plasm and under 

 essentially similar conditions as in the case of each 

 of the two parents, and there is no reason to suppose 

 that special "factors" have anything to do with it. 



We thus see how new unit characters mav be added 

 by mutation and interchanged by hybridisation while 

 the fundamental constitution of the organism remains 

 the same and the epigenetic course of development is 

 not seriously affected. All characters that arise in 

 this way rnust be regarded, from the point of view of 

 the organism, as chance characters due to chance 

 modifications of the germ-plasm, and they appear to 

 have comparatively little influence upon the course of 

 evolution. 



One of the most remarkable features of organic 

 evolution is that it results in the adaptation of the 

 organism to its environment, and for this adaptation 

 mutation and hybridisation utterlv fail to account. 

 Of course the argument of natural selection is called 

 in to get over this diflficultv. Those organisms which 

 happen to exhibit favourable mutations will survive 

 and hand on their advantages to the next generation, 



NO. 2340, VOL. 94] 



and so on. It has frequently been pointed out that 

 this is not sufficient. Mutations occur in all direc- 

 tions, and the chances of a favourable one arising 

 are extremely remote. Something more is wanted, 

 and this something, it appears to me, is to be found 

 in the direct response ot the organism to environ- 

 mental stimuli at all stages of development, whereby 

 individual adaptation is secured, and this individual 

 adaptation must arise again and again in each suc- 

 ceeding generation. Moreover, the adaptation must, 

 as I pointed out before, tend to be progressive, for 

 each successive generation builds upon a foundation 

 of accumulated experience and has a better start than 

 its predecessors. 



Of course natural selection pla3s its part, as it must 

 in all cases, even in the organic world, and I believe 

 that in many cases — as, tor example, in protective 

 resemblance and mimicry — that part has been an 

 extremely important one. But much more important 

 than natural selection appears to me what Baldwin ^ 

 tias termed "Functional Selection," selection by the 

 organism itself, out of a number of possible reactions, 

 of just those that are required to meet any emergency. 

 As Baldwin puts it, " It is the organism which secures 

 from all its over-produced movements those which are 

 adaptive and beneficial." Natural selection is here 

 replaced by intelligent selection, for I think we must 

 agree with Jennings * that we cannot make a dis- 

 tinction between the higher and the lower organisms 

 in this respect, and that all purposive reactions, or 

 adjustments, are essentially intelligent. 



Surely that much-abused philosopher, Lamarck, was 

 not far from the truth when he said, "The produc- 

 tion of a new organ in an animal body results from 

 a new requirement which continues to make itself 

 felt, and from a new movement which this require- 

 ment begets and maintains." '•• Is not this merely 

 another way of saying that the individual makes 

 adaptive responses to environmental stimuli? Where 

 so many people fall foul of Lamarck is with regard to 

 his belief in the inheritance of acquired characters. 

 But in speaking of acquired characters Lamarck did 

 not refer to such modifications as mutilations ; he was 

 obviously talking of the gradual self-adjustment of the 

 organism to its environment. . 



We are told, of course, that such adjustments will 

 only be preserved so long as the environmental stimuli 

 by which they were originally called for continue to 

 exercise their influence. Those who raise this objec- 

 tion are apt to forget that this is exactly what happens 

 in evolution, and that the sine qua non of development 

 is the proper maintenance of the appropriate environ- 

 ment, both internal and external. Natural selection 

 sees to it that the proper conditions are maintained 

 within very narrow limits. 



A great deal of the confusion that has arisen with 

 regard to the question of the inheritance of acquired 

 characters is undoubtedly due to the quite unjustifi- 

 able limitation of the idea of " inheritance " to which 

 we have accustomed ourselves. The inheritance of 

 the environment is, as I have already said, just as 

 important as the inheritance of the material founda- 

 tion of the body, and whether or not a newly acquired 

 character will be inherited must depend, usually at 

 any rate, upon whether or not the conditions under 

 which it arose are inherited. It is the fashion now- 

 adays to attach very little importance to somatogenic 

 characters in discussing the problem of evolution. 

 The whole fundamental structure of the body must, 

 however, according to the epigenetic view, be due to 

 the gradual accumulation of characters that arise as 

 the result of the reactions of the organism to its 



7 " Development and Evolution " (New York, 1002). p. 87. 



8 " Rehavioiir of the Lower Oreanisms" (New York, igoiS), PD. 334, 335 



9 " Histoire naturelle des Animaux sai,s Vertebres," torn, i., 1815, p. 185. 



