Ortmann.] XO^ [May 15, 



the process of natural selection, where such a remnant corresponding to 

 the "raw" material does not survive — unless a separation by natuial 

 conditions is added. 



III. The principle of Separation or Isolation, first conceived by M. 

 Wagner, is considered by nearly all authors* as a factor of minor import- 

 ance, although nearly all have conceded, that its occasional action cannot 

 be denied. It was looked upon as an additional factor now and then 

 favoring the formation of species, but not as a necessary one. In the 

 original theory of Darwin isolation is not contained as a particular factor, 

 although Darwin recognized the value of it very well, but he understood 

 it in a purely geographical sense. f As regards the formation of different 

 species he believes:j; it to be explained by the principle of divergence : 

 divergence is useful, and if there are any divergent variations within one 

 species, he says (p. 87): "They will be better enabled to seize on many 

 and widely diversified places in the polity of nature, and so be enabled to 

 increase in numbers." The introduction of this principle, however, is a 

 mere circumlocution of "differentiation of species," not an explanation : 

 we want to know, what are the causes of the divergence? If we peruse 

 Darwin's writings in this respect, we fiud that he was very near to recog- 

 nizing that separation actually eflects the divergence, § but since he under- 

 stood separation only in a strictly geographical sense, he failed to put this 

 factor in its proper place. Darwin's principle of divergence is nothing 

 else than the result of separation, and if we substitute the latter for the 

 former we shall complete Darwin's theory in a very important point. 



Even Wagner, in introducing the principle of separation, did not give it 

 its correct place within Darwin's theory, but tried on the contrary to 

 replace, at least partly, selection by separation, and farther, he conceived 

 the latter almost entirely in a purely geographical sense. Besides, he laid 

 much stress upon the prevention of the crossing of the separated groups 

 of animals, which is not at all the chief peculiarity of the action of sepa- 

 ration. So have all other aulliors|| in discussing this principle. But as 

 we have seen, separation acts chiefiyin the line, that each separated group 

 is subject to different conditions of life, and that thus the variations, the 

 directions of inheritance and natural selection become different. It does 

 not act, however, always in this manner, since separation is possible 



* I am to mention that G. Baur is almost the only author who estimate s correctly the 

 value of this principle. See the references to his papers : Gruudziige, etc., p. i;9, footnote, 

 and Science, March 6, 1896. p. 361. 



t Origin of Species, Gliaps. xii and xiii. 



I Ibid., p. 86fr. 



§ Darwiu {Orir/in of Species, pp. 98-100) u.ses even the words "confined or peculiar sta- 

 tions," and " isolated stations." On p. 169 he answers the question: "How .... can a 

 variety live side by side with the parent species ? " by the following : '• If both have become 

 fitted for slightly different habits of life or conditions, they luiglit live together" and " tlie 

 more permanent varieties are generally foiuid, as far as 1 can discover, inhabiting distinct 

 stations." 



|] For example, Haeckcl and Wcismanu : see Grumhiii/e, etc., p. 31, footnote. 



