THROUGH CUMULA.TIVE SEGRKGATIOT^". 



225 



diversity of use is found. Now this condition of separate breed- 

 ing is often secured by Industrial Segregation. In other words, 

 the law of Endeavour according to Endowment, often secures 

 Separation according to endowment ; and this gives an oppor- 

 tunity for the inheritable effects of diversity of endeavour to be 

 accumulated in successive generations ; and in this way both 

 laws conspire to produce divergent evolution. 



In the relation of these two factors we have a striking example 

 of the peculiar interdependence of vital phenomena. Diversity 

 of endowment is the cause of diversity of endeavour and of 

 Segregate Breeding, and diversity of endeavour with Segregate 

 Breeding is the cause of increased diversity of endowment. It 

 is very similar to the relation between power and exercise in the 

 individual. Without power there can be no exercise, and with- 

 out exercise there can be no continuance or growth of power. 



We, therefore, see that the effects of Industrial Segregation 

 are specially liable to be enhanced by that form of Intensive 

 Segregation which I have suggested should be called Suetudinal 

 Intension. 



Simple and familiar as the principles of Industrial Segregation 

 and Suetudinal Intension may seem, their consistent application 

 to the theory of evolution will throw new light on a wide range 

 of problems. This law of divergent evolution through Industrial 

 Segregation rests on facts that are so fully acknowledged by all 

 parties, that it seems to be a superfluous work to gather evidence 

 on the subject. It may, however, be profitable to consider briefly 

 whether the cases are frequent in which different habits of feed- 

 ing, of defence, or of nest-building become the cause of separate 

 breeding by which the same habits are maintained in one line of 

 descent without serious interruption for many geuerations. It 

 is important to remember, (1) that the separate breeding will 

 arise with equal certainty whether the diversity in the habits 

 has been initiated by original diversity in the instincts and 

 adaptations of the different variations, or by the crowding of 

 population inducing special efforts to find new resources, and 

 leading to diversity of endeavour ; and (2) that in either case the 

 result is what is here called Industrial Segregation. In the first 

 case the process is directly Segregative, while in the second case 

 it is primarily Separative, but (according to the principle dis- 

 cussed in the second section of last chapter) inevitably passes 

 into Segregate Breeding. Suetudinal Intension, or Divergent 



