THEORY OF NATURAL SELECTION 235 



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

 has risen higher in the scale of civilisation than the other; 

 and this apparently implies increased brain-power. 



We will return to Mr. Mivart's other objections. Insects 

 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 lat- 

 ter 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 ex- 

 cellent 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 neutral- 

 ise 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 perpetuate." 



But in all the foregoing cases the insects in their original 

 state no doubt presented some rude and accidental resem- 

 blance to an object commonly found in the stations frequented 

 by them. Nor is this at all improbable, considering the al- 

 most infinite number of surrounding objects and the diver- 

 sity in form and colour of the hosts of insects which exist. 

 As some rude resemblance is necessary for the first start, we 

 can understand how it is that the larger and higher animals 

 do not (with the exception, as far as I know, of one fish") 

 resemble for the sake of protection special objects, but only 

 the surface which commonly surrounds them, and this chiefly 

 in colour. Assuming that an insect originally happened to 

 resemble in some degree a dead twig or a decayed leaf, and 

 that it varied slightly in many ways, then all the variations 

 which rendered the insect at all more like any such object, 

 and thus favoured its escape, would be preserved, whilst other 

 variations would be neglected and ultimately lost; or, if they 



