236 APPENDIX II — INTENSIVE SEGREGATION. 



2. Reply to Criticism. 



In view of the examples of divergence that have been discussed in 

 this paper, I think I may state, as in my previous paper, "It is, 

 therefore, evident, that the simple fact of divergence in any case is 

 not sufficient ground for assuming that the divergent form has an 

 advantage over the type from which it diverges."* Mr. Wallace 

 has criticized this statement,! using the following words : 



It seems to me that throughout his paper Mr. GuUck omits the consideration of 

 the inevitable agency of natural selection, arising from the fact of only a very 

 small proportion of the offspring produced each year possibly surviving. * * * 

 He omits from all consideration the fact that at each step of the divergence there 

 was necessarily selection of the fit and less fit to survive; and that if, as a fact, 

 the two extremes have survived, and not the intermediate steps that led to one or 

 both of them, it is a proof that both had an advantage over the original less special- 

 ized form. 



But what if the type from which the new form diverges is surviving at 

 the same time that the new form survives ? And what if both the forms 

 are surrounded by the same environment which they use in different 

 ways? Where, then, is the proof that the newer form has an advan- 

 tage over the older form ? This was the class of facts I had been consider- 

 ing in the preceding paragraphs, which led to the conclusion criti- 

 cized by Mr. Wallace; and instead of omitting "the consideration of 

 the inevitable agency of selection," it was the very thing I was con- 

 sidering. I had pointed out that when a segregated portion of a 

 species exposed to the same environment changes its habits, learning 

 to appropriate resources that had not been previously used, it be- 

 comes a new intergenerating group "in which a new and divergent 

 form of selection is established," but that the result of the divergence 

 thus produced is not necessarily advantageous, and may for many 

 generations be somewhat disadvantageous. As I was aware that 

 many naturalists would consider it absurd to suppose that disadvan- 

 tageous or even non-advantageous instincts ever persist and become 

 the occasion of divergent selection, I referred to Darwin's opinion 

 that such might be the case with sexual instincts, and that the pro- 

 genitors of man were deprived of their hairy coat by sexual selection 

 that was, in its earUer stages, disadvantageous. I am not aware that 

 Darwin has ever attempted to show how divergent sexual instincts 

 arise and become permanently fixed as distinguishing characters of 

 varieties and species. 



* Linnean Society's Journal, Zoology, vol. xx, p. 214. 

 t Nature, vol. xxxvni, p. 491. 



