312 - EEV. J. T. GULICK ON 



Intensive Segregation, or Divergence through independent 

 Transformation. By Eev. John Thomas Gtflick. (Com- 

 municated by W. Perot Sladen, F.L.S.) 



[Eead 19th December, 1889.] 



In a previous paper on " Divergent Evolution through Cumu- 

 lative Segregation " * I have enumerated eighteen classes of 

 natural causes which produce either Separate or Segregate 

 G-eneration f, and which, in their combined action, tend to 

 produce cumulative Segregation and divergent evolution in every 

 part of the organic world. I have there shown, with sufficient 

 fulness, that cumulative Segregation always produces cumulative 

 divergence or polytypic evolution ; but I have not fully shown 

 how Separation from the first involves more or less Segregation, 

 or how Segregation, that at first divides the species into sections 

 with reference to some one endowment, is always tending toward 

 intensified Segregation in which the, sections present differences 

 in regard to an increasing number of endowments. 



After expounding the principles on which these laws of diver- 

 gence rest, I will give a few examples of divergence, calling at- 

 tention to the complete correspondence between the facts of 

 nature and the principles expounded in this and the previous 

 paper. 



Separation always involves more or less Segregation^ for no two 

 'portions of a species possess exactly the same average character. 

 "When a homogeneous species is divided into two large sections, 



* Journ. Linn. Soc, Zool. vol. xx. pp. 189-274. 



t Separate Generation, or Separation, is the indiscriminate division of a 

 species into sections that do not intergenerate. Segregate Greneration, or Se- 

 gregation, is the Independent Generation of different sections of a species when 

 the sections are composed of somewhat divergent classes of variations. Segre- 

 gation differs from Selection in that the latter denotes the exclusion of certain 

 kinds from opportunity to propagate, while the former denotes the division of 

 those that propagate into classes that are prevented from intergenerating. I 

 use intergenerate rather than interbreed that I may have a term equally appli- 

 cable to plants and to animals. Independent Generation, or the prevention of 

 intergeneration, whether it be through Separation or Segregation, I sometimes 

 call Segeneration. Darwin used Isolation as equivalent to geographical sepa- 

 ration, while later writers have sometimes used it as equivalent to Independent 

 Generation. Following Darwin, I use it for distribution in different areas, 

 especially when barriers intervene. 



