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 (.Pygcera bucephala ) as exhibiting a 
very marked resemblance to a broken piece of 
lichen-covered stick, and then come the following 
o 
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 
