XV 
THE RELATION OF FACTS TO THEORIES 
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whole theory of the origin of colour as a result of the 
action of Natural Selection. Mr. Wallace, as is well 
known, gives up Sexual Selection on the ground that 
there is no evidence that the females do exercise 
such a selection ; while if they did, the effect of their 
choice would be neutralised by the action of Natural 
Selection. The fact that the males in most animals 
are more brightly coloured than the females, Mr. 
Wallace ascribes in general terms to the “ greater 
vigour and excitability of the male ” ; if the colour 
and ornamentation be an expression of abundant 
vitality, its persistence and increase is easily accounted 
for apart from the choice of the female. The 
hypothesis of Sexual Selection is therefore as needless 
as it is unproved. Mr. Wallace then sums up his 
theory of the origin of colour in five theses, of which 
the following is a brief abstract :—Colour arises as a 
necessary result of the complex chemical constitution 
of animal tissues ; it becomes more conspicuous and 
intense as external tissues become more complicated 
in structure ; it is probable that colour development 
takes place according to definite laws of growth ; 
finally, “the colours thus produced, and subject to 
much individual variation, have been modified in 
innumerable ways for the benefit of each species.” It 
is in this way that Protective Coloration, Mimicry, etc. 
have been produced. Again, in the higher forms the 
male as compared with the female exhibits brilliant 
colours due to his greater vigour, while his mate has 
been kept plain by Natural Selection. 
Now all this is very different from the statements 
made by Mr. Poulton. Both certainly begin by 
saying that colour is originally non-significant ; but 
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