v How far Darwinism is established. 63 



some individuals, or some families for the members 

 of the same family are likely to present the same 

 variation if some families ' vary from the parent 

 stock in the direction of greater speed, others in the 

 direction of greater strength, and others again in the 

 direction of acuter scent ; these, gaining their food 

 in different ways, will tend to adopt different modes 

 of life, and probably to inhabit different parts of the 

 country. Thus natural selection will act on divergent 

 lines. Distinct races will be formed, having different 

 characters; and the separation of their lives will 

 prevent them from mingling, and keep them distinct. 



It is certain that the Darwinian process must be 

 actually operative; it is certain that spontaneous 

 variations must occur, and that the fittest must in 

 general be preserved by natural selection in the 

 struggle for life. For our present purpose it is need- 

 less to discuss the degree of importance which is to 

 be assigned to this agency. Among believers in 

 Evolution and all naturalists are now probably 

 believers in it opinions on the importance of the 

 Darwinian process as a factor of Evolution vary from 

 that of Weissmann, who thinks it has been the sole 

 and exclusive cause, to that of Mr. Seebohm, the 

 eminent ornithologist, who thinks its only effect on 

 the process of Evolution has been to increase its 

 rapidity ; x but none doubts that it has been an actual 

 factor in the evolutionary process. 



Now, this is sufficient for clearing up the difficulty 

 1 See note at end of chapter. 



