3°6 
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 absurdum , 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, we 
may take an example from humming-birds. The 
genus Eustephanus includes the species E. galeritus 
and E. fernandensis , in both of which the sexes 
