5C6 PROF. E. B. POTJLTdN : NATURAL SELECTION 



as has been already pointed out, the term synaposematic colours, 

 or common warning colours, may be conveniently applied to 

 them. 



The arguments in favour of natural selection as the explanation 

 of protective resemblance run entirely parallel with those which 

 favour it as the interpretation of mimetic resemblance and 

 common warning colours. By modifying the examples and, in 

 some cases, the form of the argument, nearly every section of 

 this paper might be converted into a defence of the former, and 

 the arguments which are strongest in support of the one are the 

 strongest in support of the other, viz. those contained in Sections 

 4, 5, 6, 7, 11, and 12. 



Under the theory of natural selection all the resemblances 

 among animals, mimetic and other, show the clearest relationship, 

 and (with the exception of the debated Epigamic colours) are to 

 be explained by the working of a common principle, viz., the 

 selection of variations which are useful in the struggle for 

 existence. Under the other theories mentioned above no such 

 grouping can be readily brought about, and mimetic resemblance 

 becomes due to one set of principles and the other resemblances 

 to another set. The majority of those who look on mimicry as 

 due to external or to internal causes, or to sexual selection, would 

 probably agree in explaining protective resemblance by natural 

 selection. And yet these latter cases, while far more common, 

 are often as detailed and as remarkable as those of mimicry. 

 Those who adopt the most extreme form of the theory of external 

 causes might perhaps maintain that the resemblance to twigs, 

 leaves, and bark is to be explained in the same manner, and would 

 thus bring protective and mimetic resemblance under the operation 

 of the same set of forces ; but few will be prepared to carry the 

 theory so far. Under the theory of internal causes it is impossible 

 to bring the two kinds of resemblance together ; for while it is held 

 by some that two or more animals may independently and with- 

 out selection arrive at corresponding points in their evolutionary 

 history, which are such as to involve mimetic re^-^emblance, no 

 one could believe that the similarity to bark or earth has been 

 produced in the same manner. Those who are inclined to accept 

 sexual selection as the explanation can only bring the two classes 

 of facts together by supposing that the appearance of some 

 minute portion of the total vegetable or mineral environment 

 has acted as a stimulus and has led one sex to select the other 



