liok — Divergent Evolution and thi Darwinian. Theory* 2fi 



of the principle of benefit being derived from divergence of 

 character conies in ; for this will generally lead to the most 

 different <>r divergent variations being preserved and accumu- 

 lated by natural selection." (Origin of Species, Chap. IV, 

 first page oi the section on the i% Probable Results of the 

 Action of Natural Selection, through Divergence of Character 

 and Extinction in the Descendants of a Common Ancestor." 

 In the sixth edition, this passage occurs on ]>]>. 90-1). The 

 connection in which this passage stands seems to indicate that 

 "the benefit derived from the divergence of character" is con- 

 sidered the cause of " the most different or divergent variations 

 being preserved and accumulated by natural selection,'' even in 

 the case of the representatives of the same species that are com- 

 peting witli each other on the same area, and are in no way 

 prevented from intercrossing. It is therefore necessary to 

 show the difficulties that heset such a theory, especially if we 

 adhere to the more general theory, that diversity in the kinds 

 of natural selection affecting a species must be due to differ- 

 ences in the environments by which it is surrounded. 



In the first place, natural selection, which is the superior 

 propagation of those best adapted to the environment, prevents 

 the interbreeding of the adapted forms that propagate with 

 the unadapted that fail of propagating; but it can never pre- 

 vent the interbreeding of those forms which through different 

 kinds of adaptation to the environment survive and propagate, 

 and, therefore, it can have no influence in producing accumu- 

 lated divergence, unless it is supplemented by some segregative 

 principle that prevents the different kinds of adaptations from 

 being interfused. In the second place, as long as we follow 

 Darwin's explanation of the causes of natural selection, we 

 must hold that the representatives of one species while sur- 

 rounded by the same environment, whether prevented from 

 intercrossing or not, will, through the uniform action of natu- 

 ral selection, be modified in the same way, if at all, and, while 

 surrounded by distinct and dissimilar environments, will be 

 modified in divergent ways; but, in this latter case, as they 

 will be prevented from competing with each other by occupy- 

 ing different areas, they can derive no advantage from diver- 

 gence of character through its preventing competition, there- 

 fore the divergence that follows must be attributed to some 

 other cause. In other words, the advantage attributed by 

 Darwin to divergence of character is freedom from competition, 

 through diversity of adaptation, and, as some degree of preven- 

 tion of crossing is necessary for permanent difference in 

 adaptations, the advantage cannot be secured unless there is some 

 cause preventing the crossing of the divergent forms. Now, 

 the prevention of crossing, if it ever arises, will be secured 



