234 THE EVOLUTION THEORY 



binations in this large and widely distributed family? Or of the 

 marvellously complex markings and colour-patterns of the butter- 

 flies? In some cases they may be protective, as is the green of 

 many parrots; in others, warning signs of unpalatability, like the 

 bright colours and contrasted markings of many Heliconiidae and 

 Eusemiidse and other butterflies with a nauseous taste : but there 

 remain a great many cases to which neither of these explanations 

 applies, which could only be regarded as pure freaks of nature if 

 we did not know that male sexual characters can be transferred 

 to the females, and that thus all the individuals of a species can 

 be totally altered in their colouring. 



Thus the occurrence not only of conspicuous, but of complicated, 

 coloration is explained. 



Darwin has shown that, in the equipment developed by the 

 males in their competition for the possession of the females, it is by 

 no means only those characters which may be considered ' beau- 

 tiful ' in themselves that have to be considered ; it is rather the 

 striking characteristics which mark their possessor and distinguish it 

 from others that are primarily important. In fact, it is the principle 

 of ' mode ' or ' fashion ' which is operative ; something new is de- 

 manded, and as far as possible something quite different from that 

 which was previously considered beautiful. Thus the starting-point 

 for such processes of selection may have been afforded by white 

 spots on a black ground, or, indeed, by any light spots on a dark 

 ground, which may have been the primitive colour in most cases. 

 If in the course of a long series of generations these spots became 

 the common property of all the males, a possibility of further 

 change was opened up as soon as a new contrast cropped up as a 

 chance variation, which would then, under favourable conditions, be 

 the starting-point of a new process of selection. Darwin has cited 

 some cases in which, from a comparison of the dress of the young bird 

 with that of the adult, we may conclude that a transformation of the 

 colouring of the whole plumage must have taken place in the course 

 of the phylogenetic history. 



In other cases the course of the process of selection has been such 

 that, though the general colouring has not been changed, variations 

 have appeared in particular regions of the body — spots or stripes 

 which accumulated through the ages and co-operated to form an 

 increasingly diverse and complex colour-scheme, such a 'marking' of 

 the animal as we may observe to-day, especially in butterflies, but 

 also in birds. 



It is a fine corroboration of the orio-in of bright colours through 



