138 On the Inconsistencies of Utilitarianism. 



Segregation produces Domestic Races^ why not Species ? 



Mr. Wallace seems to be opposed to the idea that some form 

 of isolation is essential to divergence ; but in his argument he 

 yields so much that I cannot but think his opposition is largely 

 due to his misinterpreting the theory. Mr. Romanes has 

 mentioned eight or ten forms of isolation, and Mr. Wallace 

 says I have discussed thirty-eight forms ; but neither of us 

 claim that these are the only possible forms, nor do we claim 

 that any form of this principle is essential to the transforma- 

 tion of one species into another wlien the original one disap- 

 pears in the process. The phrase " new species " as used by 

 Mr. Wallace in the following passage is ambiguous ; but the 

 second sentence seems to indicate that he is here discussing 

 divergence as well as simple transformation. He says : — 

 " Most writers consider the isolation of a portion of a species a 

 very important factor in the formation of new species, while 

 others maintain it to be absolutely essential. This latter view 

 has arisen from an exaggerated opinion as to the power of 

 intercrossing to keep down any variety or incipient species 

 and merge it in the parent stock. But it is evident that this 

 can only occur with varieties that are not useful, or which, if 

 useful, occur in very small numbers." ... (p. 144). Near 

 the end of the same chapter, after presenting arguments in 

 favour of this position, and after reviewing some of the facts 

 which I have presented concerning the divergences of Sand- 

 wich-Island land-molluscs, he remarks : — " We have, how- 

 ever, seen reason to believe that geographical or local isolation 

 is by no means essential to the ditferentiation of species, 

 because the same result is brought about by the incipient 

 species acquiring different habits or frequently a different 

 station, and also by the fact that different varieties of the same 

 species are known to prefer to pair with their like, and thus 

 to bring about a physiological isolation of the most effective 

 kind" (p. 150). Except that he has used "physiological 

 isolation " where I should have used psycliological segrega- 

 tion, this last passage is as completely in accord vvitli what I 

 have presented in my paper on " Divergent Evolution " as it 

 could have been if he had copied my statements. But how 

 is this passage and one of similar import on page 185 to be 

 reconciled with his own statement just quoted from page 144 ? 

 On pages 217, 218, and 226, he bases his argument for the 

 importance of different coloration in closely allied species on 

 the obvious necessity for means '' to secure the pairing 

 together of individuals of the same species," if a new species 

 is to be kept " separate from its nearest allies." He here 



