jVA ture 



103 



THURSDAY, MARCH 23, 1911. 



A CRITICISM OF THE DARWINIAN THEORY. 



The Mutation Theory. Experiments and Observa- 

 tions on the Origin of Species in the Vegetable 

 Kingdom. By Prof. H. de Vries. Translated by 

 Prof. J. B. Farmer and A. D. Darbishire. Vol. ii., 

 The Origin of Varieties by Mutation. Pp. viii + 

 683. (London : Kegan Paul and Co., Ltd., igii.) 

 Price iSs. net. 



THE first volume of Prof, de Vries 's great work 

 was devoted in the main to an account of the 

 results of the experimental cultivation of an CEnothera 

 of uncertain origin, and of the conclusions he deduced 

 from them. 'The second volume is more general in 

 its scope, and is in effect a criticism of the Darwinian 

 theory. The two might conveniently have been pub- 

 lished in the reverse order. That, at any rate, will 

 be found the best way to read them to get a clear 

 idea of the author's point of view. 



It is remarkable that pangenesis, the part of 

 Darwin's theory which was received with least en- 

 thusiasm at the time of its publication, now almost 

 overshadows all the rest. As Strasburger remarks : — 



"Darwin's idea that invisible gemmules are the 

 carriers of hereditary characters, and that they 

 multiply by division, has been removed from the posi- 

 tion of a provisional hypothesis to that of a well- 

 founded theory." 



De Vries thinks that the phenomena of variability 

 and mutation follow deductively. And for this he 

 claims the support of Darwin himself, who points 

 out ("Variation," ii., 396), "on the hypothesis of 

 pangenesis that variability depends on at least two 

 distinct groups of causes " : — (i) when the gemmules 

 are unmodified, but deficient or superabundant, or 

 are rearranged, or become active after being dor- 

 mant ; (ii) when they are modified through changed 

 conditions. The former, Darwin thought, explained 

 "much fluctuating variability"; the latter, the ap- 

 pearance of "new and changed structures." It is 

 worth notice that Darwin uses here the word "muta- 

 tion," but only apparently in the algebraic sense of 

 permutations of the gemmules. 



It is interesting to compare with Darwin's con- 

 clusion the form in which de Vries restates it in 

 terms of his own views. I have inserted for clearness 

 the corresponding numbers : — 



" (i) Numerical changes of the pangenes are . . . 

 the basis of fluctuating variability. Changes of the 

 position of the pangene in the nucleus lead to the 

 retrogressive and degressive mutations ; (ii) whilst to 

 account for progressive mutation we must assume the 

 formation of new types of pangenes " (p. 645). 



To de Vries, " fluctuating variability is a function 

 tif nutrition." It is also "linear, and oscillates only 

 in a plus and minus direction." Mutation, on the 

 other hand, "necessarily assumes a variability in all 

 directions." It seems abundantly clear that "fluctuat- 

 ing variability " has by no means the same meaning 

 to Darwin and to de Vries, It must be explained 

 that in retrogressive mutation, characters become 

 NO. 2160, VOL. 86] 



latent; in degressive, latent characters become active 

 (p. 72).^ De Vries states (p. 56) that 



" one of the chief objects of the book is to show that 

 ordinary or fluctuating variability does not provide 

 material for the origin of new species." 



But if it is merely a case of an individual organism 

 being a little better or a little less nourished, I do not 

 know that I should disagree. Darwin, however, 

 would certainly not have agreed that ordinary 

 variability was linear, or that, seeing he traced its 

 cause to " changes of any kind in the conditions of 

 life," that it was dependent exclusively on nutrition. 

 The conditions throughout a population can never be so 

 uniform that some amount of fluctuating variability' 

 is not excited. But if they are constant on the aver- 

 age, there is no resultant selective action. Thus the 

 flora of Egypt has remained stable since at least the 

 date of the Trojan war. 



De Vries is extremely anxious to make Darwin 

 responsible for the mutation theory, " It was Dar- 

 win who first attempted in various cases to distin- 

 guish between " mutability and variability. It is 

 quite true that Darwin distinguished between the 

 multiplication or reshuffling of his pangenes and their 

 modification. But there is no warrant for asserting 

 that he thought the former played no part in the 

 origin of species. He assumed that "variability of 

 every kind is directly or indirectly caused by changed 

 conditions of life" ("Variation," ii., 255). Without 

 variation, "natural selection can do nothing." All 

 that he conceded was that variation might have a 

 considerable range. But he was far from rejecting 

 the efficiency of fluctuating variability. "Under the 

 term ' variations ' it must never be forgotten that 

 mere individual differences are included" ("Origin," 

 sixth edition, p. 64); "natural selection is daily and 

 hourly scrutinising, throughout the world, the 

 slightest variations" {I.e., p, 65). 



Another misconception, for which, however, de 

 Vries is not responsible, is that Darwin's theory of 

 pangenesis ultimately led him to a modified accept- 

 ance of Lamarckism, i.e. that new structures might 

 arise in direct response to the environment. De Vries 

 himself would not accept this. In Darwin's view, 

 the modified pangenes would simply supply material 

 for more ample variation, but natural selection would 

 still determine the result, 



De Vries is convinced, nevertheless, that Darwin 

 was at heart a mutationist, and that his belief in 

 discontinuous variability "under Wallace's influence 

 gradually shifted into the background," There seems 

 here to be a double misconception, which it is not 

 difficult to clear up. Darwin, writing to Wallace in 

 i86g, said : — 



" I always thought individual differences more im- 

 portant than single variations, but now I have come 

 to the conclusion that they are of paramount import- 

 ance, and in this I believe I agree with you ( Life 

 and Letters," iii,, P- 107)- 



It is clear that by individual differences he means 

 fluctuating variability. He was preparing at the time 



1 This seems explicitly stated ; I cannot reconcile it, however, with the 

 equally explicit statement on p. 576. where the meanings of progressive and 

 degressive appear to be interchanged. 



