BUTTERFLIES AND MOTHS AS EVIDENCE OF 



EVOLUTION 



By Edward Bagnall Poulton 



Hope Projessor of Zoology h? the University oj Oxford 



On the wings of butterflies "nature writes, as on a tablet, 

 the story of the modifications of species. ... As the laws of 

 nature must be the same for all beings, the conclusions fur- 

 nished by this group of insects must be applicable to the 

 whole organic world." (H. W. Bates.) 



In spite of my title and my quotation from the great nat- 

 uralist of the Amazon I must at the outset consider for a 

 moment the evidence by which the belief in any scientific 

 theory is justified. Why do we believe that the theory of 

 the movements of the planets and satellites in our solar sys- 

 tem is true? We believe it because by the light of this theory 

 astronomers can predict the future, and we know from 

 experience that their predictions will be verified. Farseeing 

 people years ago made arrangements for observations on 

 June 29, 1927, because they had been told by astronomers 

 that on that day the moon would come between the sun and 

 the earth, that its shadow would sweep across England from 

 Southport to Hartlepool, and that every place in succession 

 on that line would be, for about 25 seconds, buried in the 

 darkness of total eclipse. And at the precise moment we 

 saw, just as predicted, its sudden onset and swift passing 

 away, while, in favored places where fortunately the astron- 

 omers had erected their instruments, the clouds cleared and 



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