948 



SCIENCE. 



[N. S. Vol. XXIII. No. 599. 



mutation theory, and although, in general, his 

 remarks and criticism appear to me well sup- 

 ported, he does not emphasize enough the fact 

 that de Vries has entirely wrong ideas with 

 regard to the process of species-making (spe- 

 ciation), and that he confounds it with 

 variation. Indeed, Vaughan points out (p. 

 684) that de Vries's conception of species 

 (elementary species) is inadequate; but he 

 fails to see that this is a vital part of the mu- 

 tation theory, and that the latter stands and 

 falls with it. 



In addition, I should like to express here a 

 few opinions, which diifer slightly from those 

 set forth by Vaughan, and which I shall try to 

 substantiate in the following paragraphs. The 

 first is, that I think the theories of Darwin 

 and of Weismann to be fundamentally differ- 

 ent, Weismann always having incorrectly un- 

 derstood Darwin's view; thus it is impossible 

 to regard the theory of Weismann as a kind 

 of an amendment to that of Darwin, and to 

 oppose both to the Lamarckian view; the 

 second is, that I believe that the inheritance of 

 acquired characters is an assumption that is 

 ' entitled to respect and consideration ' (Dall) 

 not only because it is apt to explain certain 

 facts, but chiefly so because it is the only theory 

 that is based upon sound philosophical prin- 

 ciples, the alternative theory being Jogically 

 deficient. Besides, there is a third point, to 

 which I object, namely, that Vaughan claims 

 that ' the great value of de Vries's work con- 

 sists in having shown that the origin of species 

 is an object of experimental investigation.' I 

 do not need to discuss this here again, since 

 I have shown lately ' that de Vries's experi- 

 ments have no relation at all to the making of 

 species (speciation), but only to the question 

 of variation, and that they belong to a class 

 of experiments that was known long ago. 



I. The Darwinian theory has always been 

 misinterpreted by Weismann in so far as he 

 claimed that the emphasis laid by him upon 

 natural selection, the ' all-sufficiency ' of the 

 latter, is the original Darwinian idea. But 

 a perusal of Darwin's writings shows that, al- 

 though he emphasizes natural selection as a 

 new principle discovered by himself, he does 



"Science, May 11, 1906, p. 746. 



not mean to say that it is the 07ily factor in 

 evolution.' This is seen at once by the fact 

 that three chapters (1, 2, and 5) of the 

 ' Origin of Species ' are devoted to another 

 factor, variation, while the struggle for life 

 and natural selection are treated in the chap- 

 ters 3 and 4 ; and on p. 100 (' Origin of Spe- 

 cies '), at the end of the fourth chapter, Dar- 

 win condenses his ideas upon half a page in a 

 summary, mentioning three factors: varia- 

 tion; struggle for life (resulting in natural 

 selection) ; and inheritance. 



I have shovsra previously" that Darwin also 

 perceived that another question was to be 

 settled, that of the differentiation into species 

 (speciation) ; but with regard to this his ideas 

 were somewhat hazy (' Origin of Species,' 

 chapters 12 and 13). In my opinion, this 

 point in Darwin's theory is the one that 

 needed further elucidation, and this lack has 

 been supplemented by M. Wagner by his sepa- 

 ration theory. 



That Darwin has been correctly understood 

 by others in so far as it was seen that evolu- 

 tion is influenced by different, independent 

 factors, is clearly shown by the exposition of 

 his views as given, for instance, by Haeckel. 

 I remember well, almost a quarter of a cen- 

 tury ago, when I attended Haeekel's lectures 

 on general zoology, that he made it a special 

 point to bring home the idea that evolution 

 as a general process in nature is not a theory, 

 but a logical deduction from three well-estab- 

 lished facts. The same view is found in 

 Haeekel's ' Natuerliche Schoepfungsgeschich- 

 te' (3d ed., 1872), where he mentions (p. 

 139) inheritance (Erblichkeit) and variation 

 (Veraenderlichkeit)" as the fundamental prop- 

 erties of the organisms, to which should be 

 added Darwin's principle of the struggle for 

 life (p. 144). 



The same three factors in evolution are 

 mentioned by Davenport (quoted by Vaughan, 

 I. C.J p. 690) as: variation, inheritance and 



* See Ortmann in Pr. Am. Philos. Soc, 35, 1896, 

 p. 187, 190. 



' Ihid., p. 182. 



° Haeekel uses variation and adaptation as 

 synonyms (see I. c, p. 197), which should be borne 

 in mind. 



