IN'IENSTYE SEGBEGATION. 373 



Segregation, but not always on diversity of natural selection, nor 

 always on exposure to different environments. 



We have found that persistent differences, whether varietal, 

 specific, or generic, are not all adaptational, for some of them 

 have no relation to utility ; and tliat adaptational differences are 

 not all advantageous, for some of them relate to adaptations that 

 would meet with equal success if the oi'ganisms should exchange 

 habitats ; but that in every case divergence, whether utilitarian 

 or non-utilitarian, whether advantageous or disadvantageous, is 

 not maintained without Independent Generation. 



Eeplt to Ceiticism. 



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 criticised this statement, using the following 

 w^ords t:— " It seems to me that throughout his paper Mr. Grulick 

 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 hoth had an advantage over the original less 

 specialized 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 advantage over the older form ? 

 This was the class of facts I had been considering in the preceding 

 paragraphs, which led to the conclusion criticised by Mr. Wallace ; 

 and instead of omitting "the consideration of the inevitable 

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

 sidering, as will be seen by referring to p. 213. I had pointed 

 out, that when a segregated portion of a species exposed to the 



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

 t Nature, vol. xxxviii. p. 491. 



