22 CONTROLLED NATURAL SELECTION 
animal is conspicuous or inconspicuous in 
Nature, wherein all kinds of backgrounds are 
to be found, backgrounds which will render 
the most brilliantly coloured animal incon- 
spicuous, and backgrounds which will make 
the dullest easy to see. For this reason, the 
animal’s habits must be taken into account ; 
it is necessary to know whether a given 
animal is commonly or uncommonly seen 
against obliterating backgrounds. It is also 
necessary to know, for instance, in the case 
of butterflies, what are the common back- 
grounds found behind the insects on the one 
hand when they have open wings, and on the 
other, when they have closed. 
Colour rarely is used for other purposes. Metabolic 
processes may give rise to colours which are purposeless, 
apart from metabolism. Waste products which have to 
be got rid of, may be deposited on the surfaces of plants 
and animals. 
Colour may have other uses; for instance, black for the 
absorption of the sun’s heat, white for its reflection: the 
green chlorophyl of plants comes under this category. 
Reference will again be made to Habits, 
when Thayer's theory (that all animals are 
protectively coloured) is being criticised; in 
the meantime, apart from habits, certain 
generalisations of colour in Nature can be 
made. 
