xin VARIATION AND EVOLUTION 135 



to the more plentiful distasteful form would give it 

 the advantage over wahlbergi and allow it to establish 

 itself in place of the latter. On the modern Dar- 

 winian view natural selection gradually shapes 

 wahlbergi into the mima form owing to the presence 

 of A. echeria ; on the Mendelian view natural selec- 

 tion merely conserves the mima 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, though at 

 present it is uncertain which is the dominant and 

 which 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. 



It is interesting to recall that in earlier years 

 Darwin was inclined to ascribe more importance to 

 " sports " as opposed to continuous minute variation, 

 and to consider that they might play a not incon- 

 siderable part in the formation of new varieties in 



