570 PBOP. E. B. POULTON : NATURAL SELECTION 



one." Similar facts will probably be found in numerous other 

 examples of moths wbich resemble the butterflies. 



It ma,y be safely asserted that, even with our present limited 

 knowledge, Miillerian resemblance, no less than Batesian mimicry, 

 can be found in the species of groups with all degrees of affinity, 

 and that there is no ground for Mr. Blandford's contention that 

 the latter alone derives support from the facts presented by the 

 groups which include species from different orders. 



Under natural selection the interpretation of the whole series of 

 facts is perfectly valid. The dominant forms which in each locality 

 move towards each other and towards which less domioant forms 

 also move, are in some way specially defended. The principles 

 are the same when the approximation is between the species of 

 different orders or suborders, or between those which are much 

 more closely related. The Miillerian theory explains the resem- 

 blance of such large numbers of stinging insects to each other 

 and of other specially defended forms to them, whether they be 

 closely or distantly related : it also explains the resemblance of 

 the dominant HeliconincB and Ithomiincs in each locality in South 

 and Central America and of other forms to them. Batesian 

 mimicry explains the cases in which the attracted forms are not 

 specially defended. 



The conclusion which emerges most clearly is the entire inde- 

 pendence of zoological affinity exhibited by these resemblances ; 

 and one of the rare cases in which Darwin's insight into a bio- 

 logical problem did not lead him right was when he suggested 

 that a former closer relationship may help us to understand the 

 origin of m.imiery. Further confirmation of this conclusion will 

 be found in the additional details supplied in the succeeding 

 section. 



When we look at the phenomena of mimicry and common 

 warning colours as a whole, it is found that the theory of natural 

 selection is equally applicable throughout ; while the theories of 

 external causes and internal causes cannot be applied to some of 

 the most striking lesemblances, those of moths, beetles, and 

 Diptera to stinging Hymenoptera. The theory of sexual selec- 

 tion is less logically assailable on these grounds ; but with the 

 other two suggested substitutes for natural selection, it entirely 

 fails to account for the attractive force exercised by specially 

 protected forms. Under any of these three theories it is a mere 

 coincidence that the inEects which are resembled by species of all 



