INTERMEDIATES AND MUTATION THEORY 271 



The extraordinarily varied forms of P. dardanus, sub- 

 species polytropJms, on the high Kikuyu escarpment 

 (6,500-9,000 feet) in British East Africa do not support 

 the view that the mimetic patterns arose suddenly and 

 the intermediate forms from them by interbreeding. 

 Many of these transitional forms are abundant on the 

 escarpment, but are very rarely found elsewhere ; that 

 is, they have a certain peculiar geographical distribution. 

 " The Kikuyu escarpment is the only locality at present 

 known where these transitional forms make up a large 

 proportion of the females." ^ 



Such a distribution is far more consistent with the 

 interpretation that these are an ancestral set of forms, 

 such as may have existed before the different named 

 forms became as distinct as they are to-day, which have 

 been left isolated on a mountain ridge. 



One of the most varied of all these ancestral forms is 

 trimeni, which is not considered to be an intermediate 

 between two other forms of m-imetic females, but to show 

 how the female first began to depart from the ancestral 

 type like the male. That is to say, trimeni is at one end 

 of the long series of female forms, and cannot be supposed 

 to be a stage between two others. 



Thus it is seen that these intermediate forms are held 

 by both Darwinian and Mendelian to support the respec- 

 tive hypotheses of evolution, but the latter has perforce 

 to fine down his " large " variations or " sports " to such 

 a small size that they appear to be of the kind which 

 the Darwinian recognizes as " small " variations upon 

 which Natural Selection can, and apparently does, work. 



The Mutationist claims that if these differences are 

 inherited according to Mendelian laws they must be 

 of the nature of *' large " variations ; the Darwinian 

 claims that they are the " small " variations which he 



* Poulton, " Mimicry, Mutation and Mendelism," Bedrock, vol. ii, 

 p. 49. A plate in this article shows some of these Kikuyu forms. 



