IKTENSIYE SEGREGATION'. 323 



growth (as has been clearly pointed out by Mr. Eomaues *) ; and 

 still others, througb coming under new conditions iii the envi- 

 ronment or through some new habit of intelligence, become useful 

 endowments, and are brought under the preserving and accumu- 

 lating influence of Natural Selection or of Suetude. It should, 

 however, be noted that tbe development of useful specific differ- 

 ences is as much due to Independent Generation as is the de- 

 velopment of useless specific difl"erences. Diversity of Suetude 

 or of Selection does not produce divergent evolution unless 

 it cooperates witb Independent Generation. 



Selectiokal Intension, 



or Segregation and Divergence produced hy Independent 



Selection. 



That we may gain a clear apprehension of the nature and 

 influence of this principle, certain discriminations, wbicb have not 

 always been recoguized by writers on the subject, are absolutely 

 necessary ; and, for the sake of avoiding misunderstandings, it is 

 desirable that these distinctions should be represented by clearly 

 defined terms. I am fully aware that many will be opposed to 

 the introduction of new terms into the treatment of a subject 

 that has been so long and so ably discussed. If these discrimi- 

 nations were not found necessary by the author of the ' Origin of 

 Species,' or if the distinctions, so far as recognized by himself 

 and others, have been expressed in the language of ordinary de- 

 scription, why should a more accurate terminology be needed 

 now ? In reply, it may be said that the freedom from technical 

 language which is a great advantage in a work which for the first 

 time calls attention of the world to a vast subject, is a serious 

 defect when the exact relations of the subject come under 

 discussion. 



In order to secure clear thinking on the subject, I have found 

 it necessary to keep the following distinctions constantly in 

 mind : — 



(1) The Selection that results in the transformation of species 

 is not the selection of one species to the exclusion of another. 

 The breeding of the horse to the exclusion of the ass modifies 

 neither the one nor the other. It is the exclusive generation of 

 certain variations of a single intergenerating group that gradually 



* " Physiological Selection," Jouni. Linn. See, Zool. vol. xix. p. 383. 



