1 82 Orthoplasy 



atrophied organs. Such processes would make it unneces- 

 sary to accept for such cases the very doubtful retrogres- 

 sive effects attributed by Weismann to Panmixia. 



(9) It secures the effectiveness of variation in certain 

 lines, not only by keeping alive these variations from 

 generation to generation, but also by increasing the rela- 

 tive number of individuals having these variations in 

 common, until they become established in the species. It 

 thus answers the stock objection to natural selection (cf., 

 e.g.^ Henslow, NaUiral Science, VI., 1895, pp. 585 f., and 

 VIIL, 1897, pp. 169 f.) which claims that the same variation 

 would not occur at any one time in a sufficient number of 

 individuals to establish itself, except in case of great envi- 

 ronmental change or of migration. Organic selection 

 shifts the mean of a character, and this changed mean is 

 what natural selection requires (cf . Conn, The Method of 

 Evolution, pp. 75 f.). 



It aids, also, in the matter of discontinuous variation 

 — first, by allying accommodation possibly with extreme 

 variations and so making them useful; and second, by 

 presenting the appearance of discontinuous variation, as 

 mentioned in Chapter VIIL § 3 (5). 



(10) Organic selection is a segregating or isolating 

 factor, as is illustrated under (3) above. Animals which 

 make common accommodations survive and mate together. 

 In the presence of an enemy, for instance, those animals 

 which can run fast escape together ; those which can go 

 through small holes remain likewise together ; and so do 

 those hardy enough to fight, etc. This effective production 

 of separate groups is directly due to the different accommo- 

 dations respectively made in the individuals. 



