342 The Theory of Natural Selection 



is not of itself significant, but is a concomitant of an im- 

 portant but unnoticeable physiological quality. We may 

 see no particular advantage in the pattern on the wings of 

 a lady beetle, which we can distinguish only with the aid 

 of a magnifying glass, but it is not difficult to believe that 

 this pattern, insignificant though it may be in the struggle 

 for existence, is merely an outward and visible sign of a 

 significant property in one of the vital organs. 



Selection and Protective Coloration 



Among the striking examples which Darwin used to 

 illustrate the probable workings of natural selection were 

 colorations and patterns in animals. Protective coloration 

 had been observed before, and had been accepted as part of 

 nature's scheme (see pages 148 f) . In more recent times the 

 American artist. Abbot H. Thayer, made careful systematic 

 studies on the visibility of birds and mammals under differ- 

 ent conditions of illumination, and against different kinds 

 of background. He showed very clearly that in many cases 

 the distribution of pigment is definitely protective or con- 

 cealing. Bars of white break up the outlines. The white 

 bellies, on account of the shading of the under surface, pro- 

 duce a continuity of color-tone. Mottled surfaces and other 

 conditions are unquestionably effective in making the in- 

 dividual indistinguishable in his natural settings. Darwin's 

 theory raised a new question. Do those special colorings 

 furnish animals effective and advantageous concealments in 

 their everyday relations to their natural enemies and to 

 their prey? 



Cesnola attempted to find out whether the color was 

 a factor in protecting green and brown mantids, insects 

 related to grasshoppers and walking sticks. He exposed these 

 animals against green and against brown backgrounds. He 

 found that birds destroyed a larger proportion of the insects 

 placed against a disharmonious background than of insects 

 placed upon harmonious backgrounds. These results were 



