2o8 APPENDIX II — INTENSIVE SEGREGATION. 



due to changes in the organism. We find: First, that all the forms 

 of reflexive selection are due to the relations of members of the same 

 species to each other, and are liable to change without any change in 

 the environments; second, that active selection is due to change in 

 the successful use of the powers of the organism in dealing with the 

 environment and is not dependent on change in the environment; 

 third, that passive selection, which is due to the exposure of the or- 

 ganism to a different environment, is often produced by the organism's 

 entering a new environment without there being any change in either 

 the new or the old environment ; fourth, that though passive selec- 

 tion is produced by change in the environment, the more effective 

 forms of selection do not appear till the organism has so multiplied as 

 to produce what I call "dominational selection" through intense com- 

 petition between rival individuals of the same species in gaining pos- 

 session of limited resources ; and fifth, that passive selection, which 

 depends on change in the environment, also depends on variations in 

 the adaptations of the organism. 



(19) *In this enumeration of the different forms of selection I have introduced 

 certain divisions that are not given in the paper as read before the Linnean 

 Society in 1889. These are structural, dimensional, and potential selection 

 (which I have grouped with fecundal selection as forms of impregnational selec- 

 tion), and prudential selection, which stands by itself; fecundal selection was 

 discussed in the paper as originally published, under the term "fecundal inten- 

 sion." As having an influence on survival, I now recognize it as belonging among 

 the forms of selection. The active principle may appropriately be called fecundal 

 selection, and the effect it produces on an organic group may be called fecundal 

 intension. 



In preparing my table of the forms of selection I have found difficulty in decid- 

 ing where natural selection should be placed, and how wide a definition should be 

 given to it. Some biologists use it as including sexual selection, while others agree 

 with Darwin in considering sexual selection as belonging to a very different sphere, 

 seeing that changes in sexual selection depend on changes in the activities of the 

 organism and not on changes in the environment. But appeal to Darwin's 

 writings does not remove all difficulty; for, if we decide that Darwin does not 

 include sexual selection under natural selection, it still seems certain that he 

 considered certain forms of what I have called dominational selection as forms of 

 natural selection. But dominational selection is as decidedly reflexive in its 

 action as is sexual selection. If, then, sexual selection is separated from natural 

 selection, should not dominational selection also be considered as distinct ? 



As ! )arwin has in several places stated that natural selection is subject to change 

 only when external conditions change,! I have classed it as that form of environal 



*As section (19) does not occur in the original paper, it is printed in different 

 form. 



f See Origin of Species, in the two chapters on geographical distribution, ed. 6, 

 especially on page 355, where Darwin discusses the divergence of closely allied 

 species on islands within sight of each other. 



