XV THE RELATION OF FACTS TO THEORIES 305 



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 



X 



