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 OF 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 toeach 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, 
aud 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-Lamarckians 
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 OF 
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 
ns “Tamarck, His Life and Work,” by A. S. Packard. New York and London. 
Longmans, Green & Co. pp. 319, 320. ‘ 
+ Ibid., pp. 392-396 and 404-406. 
