XV THE RELATION OF FACTS TO THEORIES 303 



Darwin's view that they are due to the persistent 

 choice by the females of the most ornamental males, 

 and therefore to Sexual Selection. So that to the 

 general statement that the colours of animals are due 

 to the action of Natural Selection, we must add, 

 except in the case of the bright colours of males, 

 which are due to the action of Sexual Selection. 

 This explanation of the colours of animals is sub- 

 stantially that given by Prof Poulton in his Colours 

 of Animals. Mr. Poulton is indeed one of the most 

 thoroughgoing of all the adherents to the doctrine of 

 Natural Selection, as the following example taken 

 from his book may serve to show. He describes the 

 buff-tip moth {Pygara bucephald) as exhibiting a 

 very marked resemblance to a broken piece of 

 lichen -covered stick, and then come the following 

 sentences : — " A friend has raised the objection that 

 the moth resembles a piece of stick cut cleanly at both 

 ends, an object which is never seen in nature. The 

 reply is that the purple and gray colour of the sides of 

 the moth, together with the pale yellow tint of the 

 parts which suggest the broken ends, present a most 

 perfect resemblance to wood in which decay has 

 induced that peculiar texture in which the tissue 

 breaks shortly and sharply, as if cut, on the applica- 

 tion of slight pressure or the force of an insignificant 

 blow" {Colours of Animals, p. 57). These state- 

 ments, whatever else they do, certainly display a 

 most profound faith in the efficiency of Natural 

 Selection as a factor in evolution. The efficiency in 

 this case seems almost excessive ; one cannot help 

 wondering whether a protective resemblance which 

 was a little less laboured would not have served the 



