Chap. ^^I.] THEORY OF NATURAL SELECTION. 283 



give them. A definite answer to the latter question 

 ought not to be expected, seeing that no one can solve 

 the simpler problem why, of two races of savages, one 

 has risen higher in the scale of civilisation than the oth- 

 er; and this apparently impHes increased brain-power. 



We will return to Mr. Mivart's other objections. In- 

 sects often resemble for the sake of protection various 

 objects, such as green or decayed leaves, dead twigs, bits 

 of lichen, flowers, spines, excrement of birds, and living 

 insects; but to this latter point I shall hereafter recur. 

 The resemblance is often wonderfully close, and is not 

 confined to colour, but extends to form, and even to 

 the manner in which the insects hold themselves. The 

 caterpillars which project motionless like dead twigs 

 from the bushes on which they feed, offer an excellent 

 instance of a resemblance of this kind. The cases of 

 the imitation of such objects as the excrement of birds, 

 are rare and exceptional. On this head, Mr. Mivart 

 remarks, "As, according to Mr. Darwin's theory, there 

 is a constant tendency to indefinite variation, and as 

 the minute incipient variations will be in all directions, 

 they must tend to neutralise each other, and at first to 

 form such unstable modifications that it is difficult, if 

 not impossible, to see how such indefinite oscillations of 

 infinitesimal beginnings can ever build up a sufficiently 

 appreciable resemblance to a leaf, bamboo, or other 

 object, for Natural Selection to seize upon and per- 

 petuate." 



But in all the foregoing cases the insects in their 

 original state no doubt presented some rude and ac- 

 cidental resemblance to an object commonly found in 

 the stations frequented by them. ISTor is this at all 

 improbable, considering the almost infinite number of 



