248 APPENDIX III LETTERS PUBLISHED IN NATURE. 



of the environment, resulting in divergent forms of selection, and pro- 

 ducing additional changes ; but so long as the environment and their 

 habits of using the environment remain unchanged, their diver- 

 gences can not be due to environal selection of any kind. 



Mr. Wallace's very interesting section on "Color as a Means of 

 Recognition," taken in connection with the section on "Selective 

 Association," already referred to, and another on "Sexual Characters 

 due to Natural Selection," offers an explanation of "the curious fact 

 that prominent differences of color often distinguish species other- 

 wise very closely allied to each other " (p. 2 2 6) . His exposition differs 

 from mine in that he denies the influence of sexual selection, and at- 

 tributes the whole process to natural selection, on the ground that 

 "means of easy recognition must be of vital importance" (p. 217). 

 The reasoning, however, seems to me to be defective, because the 

 general necessity for means of easy recognition is taken as equiva- 

 lent to the necessity for a specialization of recognition marks that 

 shall enable the different varieties to avoid crossing. In the cases I 

 am considering there is, however, no advantage either for the indi- 

 vidual or the species in the separate breeding of the different varieties, 

 and even in cases where there is such an advantage for the species (as 

 there would be if the variety had habits enabling it to escape from 

 competition with the parent stock, but not preventing it from cross- 

 ing with the same), it does not appear how this liability to breed with 

 the original stock can be any hindrance to the success of the individ- 

 ual. The significant part of the process in the development of recog- 

 nition marks must be in the failure of such individuals to secure mates, 

 which is sexual selection ; or in the unwillingness of the community 

 to tolerate the company of such, which I have called social selection. 



3. Permanent Difference in Innate Adaptations not Necessarily 

 Advantageous Difference. 



It is often assumed by writers on evolution that permanent differences 

 in the methods in which a life-preserving function is performed are neces- 

 sarily useful differences. That this is not so may be shown by an 

 illustration drawn from the methods of language. The general use- 

 fulness of language is most apparent, and it is certain that some of the 

 laws of linguistic development are determined by a principle which 

 may be called "the survival of the fittest;" but it is equally certain 

 that all the divergences which separate languages are not useful 

 divergences. That one race of men count by tens on their fingers and 

 another by twenties on their fingers and toes, is not determined by 

 differences in the environments of the races, or by any advantage 



