60 THE EVOLUTION THEORY 



colouring is advantageous in the struggle for life ? And the answer, 

 from our point of view, must read : it has arisen through natural 

 selection in those species to which a sympathetic colouring is useful. 

 Thus even if the supposition that sympathetic colouring is due to 

 automatic photography on the part of the skin were correct, we 

 should still have to regard it as an outcome of natural selection : but 

 it is not correct — at least in general — as the above objection shows, 

 and as will be further apparent from many of the phenomena of 

 colour-adaptation which I shall now adduce. 



To explain sympathetic coloration, then, we must assume, with 

 Darwin and Wallace, a process of selection due to the fact that, as 

 changes took place in the course of time in the colouring of the 

 surroundings, those individuals on an average most easily escaped 

 the persecution of their enemies which diverged least in colour from 

 their surroundings, and so, in the course of generations, an ever 

 greater harmony with this colouring was established. Variations 

 in colouring crop up everywhere, and as soon as these reached such 

 a degree as to afford their possessors a more effective protection than 

 the colouring of their fellows, then natural selection of necessity 

 stepped in, and would only cease to act when the harmony with the 

 environment had become complete, or, at least, so nearly so that any 

 increase of it could not heighten the deception. 



Of course, it is presupposed in the working out this selective 

 process that the species has enemies which see. This is the case, 

 however, with most animals living on the earth or in the water, 

 unless they are of microscopic minuteness. Many animals, too, are 

 subject to persecution not only in their adult state, but at almost 

 every period of their life, and so, in general, we should expect that 

 many of them would have attained at each stage that coloration 

 of body that would render them least liable to discovery by their 

 enemies. 



And this is in reality the case : numerous animals are protected 

 in some measure by so-called sympathetic colouring, from the egg to 

 the adult state. 



Let us begin with the egg, and of course there is no need to 

 speak of any eggs except those which are laid. Of these many are 

 simply white in colour, e. g. the eggs of many birds, snakes, and 

 lizards, and this seems to contradict our prediction ; but these eggs 

 are either hidden in earth, compost, or sand, as in the case of the 

 reptiles, or they are laid in dome-shaped nests, or concealed in holes 

 in trees, as in many birds ; thus they require no protective colouring. 



In other cases, however, numerous eggs, especially of insects and 



