3o6 COLOUR IN NATURE chap. 



Mr. Wallace speaks of laws of growth as determining 

 the progressive changes seen in the development of 

 feather-markings; while Mr. Poulton tells us that 

 although pigments tend to occur in animals, it is by 

 no means certain that they would have appeared on 

 the surface apart from Natural Selection, and that 

 they tend to disappear from the surface directly they 

 cease to be useful. 



Thus, according to the school which is usually 

 known as the Darwinian, colour, wherever seen, is 

 due to the favouring influence of Natural Selection, 

 and is in some way useful to the species. In the 

 view of the popularisers of the subject, it therefore 

 becomes the main object of the naturalist to invent 

 as ingenious an explanation as possible of the way 

 in which it is useful. If the naturalist's powers 

 of invention fail, though this happens but rarely, 

 then the colour is non-significant, or better still, the 

 animal has recently changed its habitat, and is no 

 longer perfectly adapted to its environment. The 

 theory is, therefore, perfectly complete and coherent, 

 and persons refusing to accept it are at once stigma- 

 tised as laboratory-made scientists, ignorant of nature, 

 and unworthy of the name of naturalist. 



Mr. Wallace's modified views, if less capable of a 

 reductio ad dbsurdum, are apparently less completely 

 logical. As noticed by Professor Geddes and Mr. 

 Thomson, in their Evolution of Sex, the denial of 

 Sexual Selection has a considerable bearing upon 

 Natural Selection in general. To illustrate this, -ye 

 may take an example from humming-birds. The 

 genus Eustephanus includes the species E. galeritus 

 and E. fernandensis, in both of which the sexes 



