9 



From BEDROCK, Vol. II., No. 1, April, 1913, pp. 42—56. 



MIMICRY, MUTATION AND 

 MENDELISM 



By Professor E. B. Poulton, F.R.S. 



In the first number of Bedrock the origin and growth of a 

 mimetic resemblance was considered in relation to the theories of 

 Charles Darwin and Henri Bergson. I now propose to describe 

 and illustrate further recent discoveries in the same subject, and 

 to discuss their bearing upon the place of Mutation and of Men- 

 delism in evolution. A brief account of the theories of mimicry 

 was given in the article already referred to. On the present occasion 

 it is only necessary to point out that, although the growth of a 

 mimetic pattern on the wings of a butterfly is a very short and a 

 very late chapter of evolutionary history, the record is, within its 

 limits, remarkably complete. The mutationist believes that evolu- 

 tion proceeds discontinuously by large steps. A fully formed 

 mimetic pattern may certainly strike the observer as a large step, 

 but its significance is magnified by the nature of the appeal that is 

 made to us by the sense of sight. Mutationists and Mendelians 

 have sometimes shown a tendency to yield to this appeal, and to 

 measure the evolutionary importance of a change by the depth of 

 a subjective impression. No effect caused by the presence or 

 absence or the distribution of certain superficial colours can be 

 compared for importance with changes involving such systems as 

 the nervous, muscular, and skeletal. If it were possible to prove 

 that a mimetic pattern arose fully formed and complete by a sudden 

 mutation, it would by no means follow that more deeply-seated 

 changes have been brought about in the same way. If, on the 

 other hand, it can be shown that a likeness was evolved by the 

 progressive modification of a series of stages, strong grounds will be 

 afforded for the belief that more fundamental changes were effected 

 gradually and not suddenly. 



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