178 MENDELISM chap. 



occurred where A. dominicanus was common and 

 A. echeria was rare, its resemblance to the more 

 plentiful distasteful form would give it the advan- 

 tage over mima and allow it to establish itself in 

 place of the latter. On the modern Darwinian 

 view natural selection gradually shapes mima into 

 the wahlbergi form owing to the presence of A. 

 dominicanus ; on the Mendelian view natural selec- 

 tion merely conserves the wahlbergi form when once 

 it has arisen. Now this case of mimicry is one 

 of especial interest, because we have experimental 

 evidence that the relation between mima and 

 wahlbergi is a simple Mendelian one, mima here 

 being the dominant and wahlbergi the recessive 

 form. The two have been proved to occur in 

 families bred from the same female without the 

 occurrence of any intermediates, and the fact that 

 the two segregate cleanly is strong evidence in 

 favour of the Mendelian view. On this view the 

 genera Amauris and Euralia contain a similar set 

 of pattern factors, and the conditions, whatever they 

 may be, which bring about mutation in the former 

 lead to the production of a similar mutation in the 

 latter. Of the different forms of Euralia produced 

 in any region that one has the best chance of 

 survival, through the operation of natural selection, 

 which resembles the most plentiful Amauris form. 

 Mimetic resemblance is a true phenomenon, but 

 natural selection plays the part of a conservative, 

 not of a formative agent.^ 



^ The reader who is interested in this subject will find it discussed 

 more fully in my book on Mimicry in Butterflies. Cambridge Univer- 

 sity Press, 19 1 5. 



