CAUSES AND EFFECTS OF SEGREGATION. 7 



tial factor in the production and maintenance of divergent types, 

 whether they be varieties or species; and any theory that fails to 

 consider the causes and effects of isolation is an insufficient explana- 

 tion of divergent evolution. Still further, as the general trend of all 

 evolution is toward increasing divergence, the influence of isolation 

 is fundamental in all the processes of organic evolution. 



IV. Investigation op the Causes and Effects of Segregation. 



The purpose of this volume is to investigate the causes and effects 

 of what I have called "segregate breeding," or simply "segregation." 

 Segregation is the intergeneration of like with like, with the preven- 

 tion of crossing between unlike groups. I maintain that segregation 

 ranks as one of the fundamental principles controlling the relations 

 of organic beings to each other. Moreover, in the processes of organic 

 evolution, the principles controlling the modification of segregation 

 are the principles that control the variation and heredity. It is only 

 as it aids in producing and intensifying segregation that any form of 

 selection becomes effective in the evolution of organic types. I 

 maintain that the inheritance of acquired characters is not yet fully 

 proved or disproved; but if future investigation should show that 

 the special training of parents for several generations results in the 

 transmission to offspring of modified innate endowments, there could 

 be no doubt that to gain the full effect of such training on offspring 

 there must not be free crossing between the trained and the untrained. 

 Segregation, even under such conditions, remains a leading factor, 

 and modification of segregation will, I believe, be found to be the 

 principle controlling the evolution. 



Lamarck recognized that distinct organic types could not be main- 

 tained without some form of isolation;* and such Neo-I/amarckians 

 as Professor Packard have been even more emphatic in placing this 

 principle among the essential conditions for divergent evolution, t 



V. Segregation the Unifying Principle in the Complex Process op 



Evolution. 



If heredity is a fundamental power, then segregate breeding must 

 be a fundamental principle in the formation, continuance, and control 

 of divergent types; for diversity of type is diversity of inheritance, 

 and diversity of inheritance can not be initiated or maintained where 



* "Lamarck, His Life and Work," by A. S. Packard. New York and London. 

 Longmans, Green & Co. pp. 319, 320. 

 t Ibid., pp. 392-396 and 404-406. 



