CHAPTER VIII 



THE CASE OF PAPILIO POLYTES (cont.) 



It was suggested in the last chapter that if a new 

 variation arose as a sport — as a sudden hereditary 

 variation— and if that variation were, through resem- 

 blance to a different and unpalatable species, to be more 

 immune to the attacks of enemies than the normal 

 form, it was conceivable that the newer mimetic sport 

 would become established, and in time perhaps come 

 to be the only form of the species. We may suppose, 

 for example, that the A female of P. polytes arose 

 suddenly, and that owing to its likeness to the pre- 

 sumably distasteful P. aristolodiiae it became rapidly 

 more numerous until in some localities it is the common- 

 est or even the only form. However, before discussing 

 the establishing of a mimetic form in this manner we 

 must first deal with certain general results which may 

 be expected to follow on a process of selection applied 

 to members of a population presenting variations 

 which are inherited on ordinary Mendelian lines. 



Let us suppose that we are dealing with the in- 

 heritance of a character which depends upon the pre- 

 sence of the genetic factor X ; and let us also suppose 

 that the heterozygous form (Xx) is indistinguishable 



