EFFECTS OF SELF-FERTILIZATION 93 



commonly received hypothesis that assumes the dangers 

 of continued breeding between near of kin. A. R. Wal- 

 lace speaks of these facts in Darwinism} and I have 

 drawn attention to them in discussing the meaning of 

 insect migration, although, as will be seen in the follow- 

 ing passage, without any serious doubt as to the physio- 

 logical significance of cross-fertilization. 2 



' We may well inquire why it should be necessary for 

 such emigration, with a possible successful issue in coloni- 

 zation, to require the services of countless individuals 

 when the importation of half a dozen rabbits or a few 

 specimens of Pieris rapae will, for the naturalist, change 

 the face of a continent. The results of these unin- 

 tentional, or intentional but ill-considered, experiments 

 do indeed shake the belief in the paramount necessity 

 for crosses and the dangers of in-and-in breeding ; but 

 the end is not yet, and the teeming colonies which have 

 arisen from such small beginnings may in time vanish 

 from the operation of deep-seated causes. The varied 

 adaptations for cross-fertilization and the prevention 

 of in-and-in breeding are so evident in nature, that we 

 are compelled to believe that they meet and counteract 

 serious dangers which sooner or later would menace 

 the very existence of the species.' 3 But now the considera- 

 tions set forth in this and the preceding Section throw 

 doubt upon the existence of such serious dangers and the 

 reality of any such compulsion. 



It is impossible to do more than mention certain advan- 

 tages which may have favoured cross-fertilization, if here- 

 after the generally accepted physiological necessity turn out 

 to be a delusion. Brief reference may, however, be made 

 to the special advantages of community which are possible 

 through Syngamy alone. By interbreeding the favourable 

 variations arising in one direction are combined with 

 others arising in different directions ; by the kaleidoscopic 

 changes produced by interbreeding more varied results 

 are presented for selection, and the beneficial qualities 

 arising in one part of the mass may quickly become 



1 p- 326. 2 Trans. Ent. Soc. Lond,, 1902, pp. 460-65. 



3 loc. cit. p. 464. 



