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. 



Eeference 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. 



